Since the bicuspid anatomy commonly has an almost normal valve function (unless deformed) it is left bicuspid; the repair procedure simply corrects the secondary deformations that led to regurgitation.
Similar to tricuspid aortic valves, the cusps must be measured to rule out shrinkage. The annulus is commonly enlarged, it must be reduced and stabilized by an annuloplasty. [ 12 ]  Tissue redundancy through stretching is corrected by sutures.


The unicuspid aortic valve may not only result in relevant stenosis (narrowing), it may also primarily lead to regurgitation. In a proportion of the affected individuals, an aneurysm of the ascending aorta may be present which may need treatment as well. The repair procedure will change the configuration of the valve by creating at least one additional commissure. Commonly the unicuspid valve is changed into a bicuspid configuration; the resulting valve function will be close to normal. Cusp tissue is resected where it is grossly abnormal. Using patch tissue, the cusps are enlarged so they reach the second (new) commissure. If the annulus is enlarged it must be reduced and stabilized. [ 12 ]


Aortic regurgitation in a quadricuspid valve is commonly caused by the additional (4th) commissure, which holds back cusp tissue and keeps it from closing adequately. Currently, the most reliable concept for repair of a quadricuspid valve seems to be its conversion into a tricuspid valve. [ 13 ]  In some cases a bicuspid configuration may be appropriate. In order to achieve this cusp, tissue is detached from the aorta and the valve is then brought into adequate form.


The enlargement of the  ascending aorta  may lead to aortic valve regurgitation because the outward tension on the cusps prevents their adequate closure. Regurgitation may also (in part) be due to congenital malformation of the aortic valve or concomitant stretching of a tricuspid aortic valve. Life expectancy may be limited by severe aortic regurgitation. The aneurysm of the ascending aorta may also become so large that it can develop rupture or dissection as life-threatening complications. [ citation needed ]


The operation must address the aneurysm by replacing the enlarged part of the aorta. Since the aortic valve is very sensitive in its form and function to any changes of the aortic dimensions, the operation will in most cases also have to address the valve, i.e. apply the principles of aortic valve repair. This principle applies to tricuspid valves as well as bicuspid or unicuspid aortic valves. [ 14 ] [ 15 ]


The goal of the operation is to eliminate the aneurysm and to preserve or repair the aortic valve. The operation may include replacement of the aortic root. Replacement of the root is usually not necessary if its diameter is less than 40 to 45 mm. In those instances replacement of the ascending aorta is sufficient. If root diameter exceeds 45 mm it will have to be replaced in many instances. There are mainly 2 operative techniques currently used, [ 16 ] [ 17 ]  and both lead to similar results. [ 18 ] [ 19 ]  With both techniques the aortic valve must be carefully assessed after replacement of the root; repair of any aortic valve abnormalities is necessary in order to achieve good and durable valve function. [ 19 ] [ 20 ]


There are two options: tubular ascending aortic replacement or replacement of the aortic root.


Tubular ascending aortic replacement


The aorta is divided above the aortic valve and root. The avascular graft is then sutured to the aortic root. The form of the aortic valve may have been changed by this maneuver, it thus has to be carefully checked. Often stretching of a cusp becomes apparent at that point, and this will have to correct by sutures (see 3.3.1, 3.3.2).


Replacement of the aortic root


After the heart has been arrested, the enlarged aorta is removed close to the insertion line of the aortic valve cusps. The origins of the coronary arteries must be detached from the aorta. For the procedure, according to  Magdi Yacoub [ 16 ]  a graft is tailored to create 3 tongues that replace the aneurysmatic aortic wall in the root. The graft is then sutured to the cusp insertion lines. Some surgeons combine this procedure with an  annuloplasty . [ 12 ] [ 21 ]  For the procedure according to  Tirone David , [ 17 ]  the aortic valve is mobilized even further from the surrounding tissues. The avascular graft is then positioned around the valve, and the valve is fixed inside the graft with sutures.


With both techniques, the form of the aortic valve must be carefully assessed after completed root replacement. [ 22 ]  In most instances some cusp stretching will be found which would result in prolapse and relevant regurgitation afterward if uncorrected. Thus an aortic valve repair procedure will frequently be necessary according to the principles of tricuspid or bicuspid aortic valve repair.


Contrary to valve replacement with mechanical prostheses inhibition of the blood clotting system ( anticoagulation ) is not necessary after aortic valve repair. Blood-thinning may only be necessary if atrial fibrillation occurs or persists in order to prevent blood clot formation in the left atrium. [ citation needed ]


Following aortic valve replacement, prophylactic administration of  antibiotics  is recommended for interventions involving mouth and throat (e.g. dental surgery). [ 4 ]  It is unclear whether this is also necessary after aortic valve repair.


First attempts at aortic  valve repair  were undertaken even before heart valve prostheses were developed. In 1912 the French surgeon  Theodore Tuffier  widened a stenotic (narrowed) aortic valve. The colleagues of  Dwight Harken  reported in 1958 on their experience with aortic valve repair for aortic regurgitation by narrowing the  annulus  of the  aortic valve . [ 23 ]  In those times, both surgeons and cardiologists had minimal information on the exact nature and severity of dysfunction of the aortic valve. This changed with the development of  echocardiography  by  Inge Edler  and  Carl Hellmuth Hertz  in the early 1950s. Nonetheless, the development of heart valve prostheses made replacement the standard approach because of its reproducibility. The first ball-cage valve was implanted in 1961 by the American surgeons   Albert Starr  and  Lowell Edwards , [ 24 ]  and in the next decades many mechanical and biological  prostheses  were developed and used. The positive results with the repair of the  mitral valve  stimulated surgeons in the 1980s and 1990s to develop surgical techniques that could be applied for the different causes of aortic regurgitation. Stepwise improvements were introduced in the subsequent years; today many regurgitant aortic valves can be treated by repair.


Aortic valve replacement  is a  cardiac surgery  procedure whereby a failing  aortic valve  is  replaced  with an  artificial heart valve . The aortic valve may need to be replaced because of  aortic regurgitation  (back flow), or if the valve is narrowed by  stenosis .


Current methods for aortic valve replacement include  open-heart surgery ,  minimally invasive cardiac surgery (MICS) ,  surgical aortic valve replacement  (SAVR) and  percutaneous or transcatheter aortic valve replacement  (TAVR; also PAVR, PAVI, TAVI).


A cardiologist can evaluate whether a  heart valve repair  or  valve replacement  would be of benefit. [ 1 ]


During the late 1940s and early 1950s, the first surgical approaches towards treating aortic valve stenosis had limited success. The first attempts were valvotomies, (i.e. cutting the valve while the heart is pumping). A ball valve prosthesis placed on the  descending thoracic aorta  (heterotopically) was developed by Hufnagel, Harvey and others to address aortic stenosis, but had disastrous complications. Later, with the innovation of cardiopulmonary bypass, the ball valve prosthesis was placed orthotopically (i.e. in same place as the original aortic valve). This first generation of prosthetic valves was durable, but needed intense anti-coagulation, and cardiac hemodynamics were compromised. During the mid-1950s, a single-leaflet prosthesis was developed by Bahnson  et al . In early 1960, Ross and  Barratt-Boyes  used allografts. Tissue prosthetic valves were introduced in 1965 by Binet in Paris, but they degenerated quickly because the tissue was insufficiently preserved. Carpentier solved this problem by introducing glutaraldehyde-preserved stent-mounted porcine valves. [ 2 ] [ 3 ]


The aortic valve is one of the two  semilunar valves  of the heart with three cusps. It separates the heart from the  aorta . Each cusp is attached to the aortic wall creating a sinus called an  aortic sinus . The origins of the two  coronary arteries  are sited in two aortic sinuses. Cusps also known as leaflets are separated by  commissures . The posterior leaflet is in continuation with the anterior leaflet of the mitral valve (the tissue is called the aorto-mitral curtain). [ 4 ]  The aortic valve is opened during systole, the driving force for it to open is the difference in pressure between the contracting left ventricle of the heart and the aorta. During cardiac diastole (when the heart chamber gets bigger) the aortic valve closes. [ 5 ]


Aortic stenosis most commonly is the result of calcification of the cusps. Other reasons for stenosis are the  bicuspid valve  (some patients have only two cusps at the aortic valve instead of the usual three) and rheumatic aortic stenosis (now rare in the West). Obstruction at the level of the aortic valve causes increased pressure within the heart's left ventricle. This can lead to hypertrophy and ultimately dysfunction of the heart. While x-ray and ECG might indicate aortic stenosis, echocardiography is the diagnostic procedure of choice. US findings also help in grading the severity of the disease. In cases of symptomatic severe aortic stenosis, AVR is warranted. In cases of asymptomatic but severe aortic stenosis, more factors should be taken into consideration. [ 6 ]


Aortic regurgitation, on the other hand, has many causes: degeneration of the cusps, endocarditis, bicuspid aortic valve, aortic root dilatation, trauma, connective tissue disorders such as Marfan syndrome or Ehlers-Danlos lead to imperfect closure of the valve during diastole, hence the blood is returning from the aorta towards the left ventricle of the heart. Acute aortic regurgitation (caused by endocarditis, aortic dissection or trauma) ends up in pulmonary edema, because of the acute increase in left ventricle (LVEDP) that does not have time to adjust to the regurgitation. Chronic regurgitation, by contrast, gives the heart time to change shape, resulting in  eccentric hypertrophy , which has disastrous effects on the myocardium. Ultrasound is here also the best diagnostic mobility, either it is transthoracic or transesophageal.  [ 7 ]


As long-term data on the survival and quality of life of people following valve replacement have become available, evidence-based guidelines for aortic valve replacement have been developed. These help healthcare professionals decide when aortic valve replacement is the best option for a patient. Two widely accepted sets of guidelines used by surgeons and cardiologists are the American Heart Association and American College of Cardiology Guidelines for the Management of Patients with Valvular Heart Disease, [ 8 ]  and the European Society of Cardiology and the European Association for Cardio‑Thoracic Surgery Guidelines for the management of valvular heart disease. [ 9 ]


Aortic stenosis  is treated with aortic valve replacement in order to avoid  angina ,  syncope , or  congestive heart failure . Individuals with severe aortic stenosis are candidates for aortic valve replacement once they develop symptoms or when their heart function is impacted. Some people with asymptomatic aortic stenosis may also be candidates for aortic valve replacement, especially if symptoms appear during  exercise testing . [ 9 ]  Patients with moderate aortic valve stenosis who need another type of cardiac surgery (i.e.  coronary artery bypass surgery ) should also have their valve addressed by the surgical team if  echocardiography  unveils significant heart problems. [ 10 ]


Low gradient aortic stenosis with concomitant left ventricular dysfunction poses a significant question to the anesthesiologist and the patient. Stress echocardiography (i.e. with dobutamine infusion) can help determine if the ventricle is dysfunctional because of aortic stenosis, or because the myocardium lost its ability to contract. [ 11 ]


Many people with  aortic insufficiency  often do not develop symptoms until they have had the condition for many years. [ 12 ]  Aortic valve replacement is indicated for symptoms such as  shortness of breath , and in cases where the heart has begun to enlarge (dilate) from pumping the increased volume of blood that leaks back through the valve. [ 9 ]


There are two basic types of replacement heart valve: tissue (bioprosthetic) valves and mechanical valves. [ 13 ]


Tissue heart valves are usually made from animal tissue (heterografts) mounted on a metal or polymer support. [ 14 ]  Bovine (cow) tissue is most commonly used, but some are made from porcine (pig) tissue. [ 15 ]  The tissue is treated to prevent rejection and calcification (where calcium builds up on the replacement valve and stops it working properly). [ 16 ]


Occasionally, alternatives to animal tissue valves are used: aortic  homografts  and pulmonary  autografts . An aortic homograft is an aortic valve from a human donor, retrieved either after their death or from their heart if they are undergoing a heart transplant. [ 17 ]  A pulmonary autograft, also known as the  Ross procedure  is where the aortic valve is removed and replaced with the patient's own  pulmonary valve  (the valve between the right ventricle and the pulmonary artery). A pulmonary homograft (a pulmonary valve taken from a cadaver) is then used to replace the patient's own pulmonary valve. This procedure was first performed in 1967 and is used primarily in children, as it allows the patient's own pulmonary valve (now in the aortic position) to grow with the child. [ 17 ]


Tissue valves can last 10–20 years. [ 18 ]  However, they tend to deteriorate more quickly in younger patients. [ 19 ]  New ways of preserving the tissue for longer are being investigated. One such preservation treatment is now being used in a commercially available tissue heart valve. In sheep and rabbit studies, the tissue (called RESILIA tissue) had less  calcification  than control tissue. Mid-term data on the safety and haemodynamic performance of the Inspiris RESILIA aortic bioprosthesis are encouraging. [ 20 ] [ 21 ]


Stented and stentless tissue valves are available. Stented valves come in sizes from 19 mm to 29 mm. [ 22 ]  Stentless valves are directly sutured at the aortic root. The major advantage of stentless valves is that they limit  patient–prosthesis mismatch  (when the area of the prosthetic valve is too small in relation to the size of the patient, increasing the pressure inside the valve [ 23 ] ) and can be helpful when dealing with small aortic root. However, stentless valves take more time than stented valves to implant. [ 24 ]


Mechanical valves are made from synthetic materials, such as titanium or  pyrolytic carbon . [ 25 ]  Their durability is long life, while tissue valves can last for up to 15–20 years. [ 26 ] [ 27 ] [ 13 ]  Since the risk of blood clots forming is higher with mechanical valves than with tissue valves, patients with mechanical heart valves are required to take anticoagulant (blood-thinning) drugs, such as  warfarin , long-life, making them more prone to bleeding (1% per year). [ 13 ]  The sound of the valve can be heard very rarely, often as clicks, and might be disturbing. [ 28 ]  The choice of prosthetic valve should be individualized, carefully considering each patient's unique circumstances. In that context, the new generation aortic mechanical valve (On-X) offers a potential lifetime solution without need for a repeat operation, while minimizing the risks of long-term anticoagulation due to reduced anticoagulation target INR of 1.5 to 2.0. [ 29 ]


Valve choice is a balance between the lower durability of tissue valves and the increased risk of blood clots and bleeding with mechanical valves. Guidelines suggest that patient age, lifestyle and medical history should all be considered when choosing a valve. Tissue valves deteriorate more rapidly in young patients and during pregnancy, but they are preferable for women who wish to have children because pregnancy increases the risk of blood clots. Typically, a mechanical valve is considered for patients under 60 years old, while a tissue valve is considered for patients over the age of 65 years. [ 13 ]


Surgical aortic valve replacement is conventionally done through a  median sternotomy , meaning the incision is made by cutting through the breastbone ( sternum ). Once the protective membrane around the heart ( pericardium ) has been opened, the patient is cannulated (aortic cannulation by a cannula placed on the  aorta  and a venous canulation by a single atrial venous cannula inserted through the right atrium). The patient is put on a  cardiopulmonary bypass  machine, also known as the heart–lung machine. This machine breathes for the patient and pumps their blood around their body while the surgeon replaces the heart valve. [ citation needed ]


Once on cardiopulmonary bypass, the patient's heart is stopped ( cardioplegia ). This can be done with a Y-type cardioplegic infusion catheter placed on the aorta, de-aired and connected to the cardiopulmonary bypass machine. Alternatively, a retrograde cardioplegic cannula can be inserted at the coronary sinus. Some surgeons also opt to place a vent in the left ventricle through the right superior pulmonary vein, because this helps to prevent left ventricular distention before and after cardiac arrest. When the set-up is ready, the aorta is clamped shut with a cross-clamp to stop blood pumping through the heart and cardioplegia is infused. The surgeon incises the aorta a few milometers above the sinotubular junction (just above the coronary ostia, where the coronary arteries join the aorta) – a process known as aortotomy. After this, cardioplegia is delivered directly through the ostia. [ 30 ] [ 31 ]


The heart is now still and the surgeon removes the patient's diseased aortic valve. The cusps of the aortic valve are excised, and calcium is removed (debrided) from the aortic annulus. The surgeon measures the size of the aortic annulus and fits a mechanical or tissue valve of the appropriate size. Usually the valve is fixed in place with sutures, although some sutureless valves are available. If the patient's aortic root is very small, the sutures are placed outside of the aortic root instead of at the annulus, to gain some extra space. [ citation needed ]


Once the valve is in place and the aorta has been closed, patient is placed in a  Trendelenburg position  and the heart is de-aired and restarted. The patient is taken off the cardiopulmonary bypass machine.  Transesophageal echocardiogram  (an ultrasound of the heart done through the esophagus) can be used to verify that the new valve is functioning properly. Pacing wires are usually put in place, so that the heart can be manually controlled should any complications arise after surgery. Drainage tubes are also inserted, to drain fluids from the chest. These are usually removed within 36 hours, while the pacing wires are generally left in place until right before the patient is discharged from the hospital. [ 30 ] [ 31 ]


After surgical aortic valve replacement, the patient will usually stay in an  intensive care unit  for 12–36 hours. Unless complications arise, the patient is then able to go home after approximately four to seven days. [ 32 ]  Common complications include disturbances to the heart's rhythm ( heart block ), which typically require the permanent insertion of a  cardiac pacemaker . [ 33 ]


Recovery from aortic valve replacement takes about three months if the patient is in good health. Patients are advised not to lift anything heavier than 10 lbs for several weeks, and not to do any heavy lifting for 4–6 months after surgery to avoid damaging their breastbone. Often patients will be referred to participate in  cardiopulmonary rehabilitation , which optimizes recovery and physical function in patients with recent cardiac surgeries. This can be done in an outpatient setting. [ 34 ]


Surgery usually relieves the aortic disease symptoms that led the patient to the operating room. The survival curve of patients who undergo aortic valve replacements is slightly inferior to the curve of their corresponding healthy same-aged same sex population. [ 35 ]  Pre-operative severe left ventricular hypertrophy is a contributing factor to morbidity. [ 35 ]


The risk of dying as a result of aortic valve replacement is estimated at 1–3%. [ 36 ] [ 37 ] [ 38 ]  Combining aortic valve replacement with coronary artery bypass grafting increases the risk of mortality. [ 36 ]  Older patients, as well as those who are frail and/or have other health problems ( comorbidities ), have a higher risk of experiencing complications. [ 37 ]  Possible problems include  cardiac infarction  or failure,  arrhythmia  or  heart block  typically requiring the permanent insertion of a  cardiac pacemaker , mediastinal bleeding,  stroke  and infection. Late complications include  endocarditis , thromboembolic events ( blood clots ), prosthetic valve dysfunction and paravalvular leak (blood flowing between the edge of the prosthetic valve and the cardiac tissue). [ 35 ]


When dealing with a small aortic annulus, the surgeon might have to insert a prosthetic aortic valve of small size, with an orifice too small in relation to the size of the patient (patient–prosthesis mismatch). This increases the pressure of the blood flowing through the valve, and can lead to worse outcomes. [ 23 ]  Various techniques, including stentless valves, have been utilized to avoid this problem. [ 39 ]


Since the late 1990s, some cardiac surgeons have been performing aortic valve replacement using an approach referred to as minimally invasive cardiac surgery (MICS). [ 40 ]  Using this approach, the surgeon replaces the valve through a smaller chest incision (6–10 cm) than that for a median sternotomy. MICS typically requires shorter recovery times, and produces less visible scarring. [ 41 ]  Alternatively, aortic valve replacement can be performed with right minithoracotomy approach via the 2nd or 3rd intercostal space. There is growing evidence that this approach can reduce postoperative morbidity allowing less blood loss, less pain,
faster recovery, and a shorter hospital stay with no difference in mortality. [ 42 ]  This approach can be particularly valuable in higher risk and elderly patients. [ 43 ]


Another alternative for many high-risk or elderly patients is transcatheter aortic valve replacement (TAVR, also known as TAVI, transcatheter aortic valve implantation). Rather than removing the existing valve, the new valve is pushed through it in a collapsed state. It is delivered to the site of the existing valve through a tube called a catheter, which may be inserted through the femoral artery in the thigh (transfemoral approach), or using a small incision in the chest and then through a large artery or the tip of the left ventricle (transapical approach). [ 44 ]  Fluoroscopy and  transthoracic echocardiogram  (TTE) are visual aids used to guide the process. [ 44 ]  Once the collapsed replacement valve is in place it is expanded, pushing the old valve's  leaflets  out of the way. [ 45 ]


Guidelines suggest TAVR for most patients aged 75 years and older, and surgical aortic valve replacement for most younger patients. [ 46 ]  Ultimately, the choice of treatment is  based on many factors. [ 47 ] [ 46 ]


Systematic reviews  have addressed this comparison: [ 48 ] [ 49 ]


Aortic valvuloplasty , also known as  balloon aortic valvuloplasty (BAV) , is a procedure used to improve blood flow through the  aortic valve  in conditions that cause  aortic stenosis , or narrowing of the aortic valve. It can be performed in various patient populations including fetuses, newborns, children, adults, and pregnant women. [ 1 ] [ 2 ]  The procedure involves using a  balloon catheter  to dilate the narrowed aortic valve by inflating the balloon. [ 1 ]


Guidelines and indications are specific to different patient populations. For adults with aortic stenosis, guidelines suggest that balloon aortic valvuloplasty (BAV) is to be used as a temporary procedure to improve blood flow through the aortic valve to alleviate symptoms and stabilize clinically before having more invasive procedures done, including  aortic valve replacement  (AVR) or  transcatheter aortic valve implantation  (TAVI). The most common conditions that deem patients too unstable for AVR or TAVI are  pulmonary edema  and  cardiogenic shock , which BAV attempts to correct to stabilize the patient before definitive surgery. [ 1 ] [ 3 ] [ 4 ] [ 5 ]  For adult patients with aortic stenosis who need noncardiac related surgeries, BAV can be indicated to decrease the risk of the operation in certain high-risk patients. [ 1 ] [ 3 ]  BAV has been used in adult patients who have shortness of breath and the cause is unclear between aortic stenosis or from a primary lung problem. These patients undergo BAV and if their shortness of breath improves, the cause is deemed to be likely from aortic stenosis and they can undergo AVR or TAVI to correct the aortic stenosis definitively. [ 3 ] [ 4 ]  BAV can also be used as  palliation  therapy to improve symptoms in patients who cannot undergo AVR or TAVI due to contraindications. [ 3 ] [ 1 ] [ 5 ]


BAV has been performed on fetuses with  congenital heart defects  involving the aortic valve to improve blood flow within the heart. It is not definitive treatment, but is performed in an attempt to prevent a condition called  hypoplastic left heart syndrome . [ 1 ]  For neonates and children with congenital aortic valve stenosis, BAV is commonly the first type of procedure performed to relieve the stenosis, but is not always a definitive treatment option. [ 6 ] [ 1 ] [ 5 ]


Guidelines suggest performing BAV in pregnant patients with severe aortic stenosis evident by severe symptoms. Changes in blood flow and circulation during pregnancy make it more likely for complications and symptoms to arise in patients with aortic stenosis. When BAV is indicated, it is suggested to attempt to wait until the  third trimester  to avoid harm to the fetal  thyroid  from the  contrast dye  needed during the procedure. [ 1 ] [ 2 ]


Aortic valvuloplasty relies on placing a catheter with a balloon at the tip in the aortic valve, which is then inflated to widen the narrowed valve. [ 1 ]  In order to reach the aortic valve, a  blood vessel  is punctured to introduce the catheter and advance it into the aortic valve. The most common site of entry is the  femoral artery  in the groin, but the  carotid artery  in the neck can also be used. The  umbilical artery  is used when the procedure is performed on a fetus. [ 1 ] [ 7 ]  There has also been success using the  radial artery  in the wrist to gain access. [ 7 ]   Ultrasound  is commonly used to visualize the vessel being accessed to avoid potential complications. [ 3 ]  A  wire  is typically used to guide the balloon catheter from the access site to the aortic valve. [ 1 ]  Different size balloons are used depending on the age of the patient. [ 1 ]  In order for the balloon to remain in the proper position while it is being inflated in the aortic valve, blood flow through the valve needs to be temporarily reduced. This is typically achieved by increasing the heart rate through  electrical stimulation of the heart muscle  or through medications that decrease blood pumping from the  left ventricle . [ 1 ]  The blood pressure and flow across the aortic valve is monitored and repeated inflation of the balloon is sometimes needed to successfully dilate the aortic valve. [ 1 ]


After BAV in adults, it is common to have both clinical and symptomatic improvement early on. Clinically, the pressure across the aortic valve is reduced, there is increased blood flow, and the area of the aortic valve is increased due to mechanical dilation of the balloon. Many patients have a reduction of the symptoms associated with severe aortic stenosis, commonly reported as an improvement of their  NYHA functional class , which is a way to categorize the severity of heart failure based on reported symptoms. [ 8 ]  The early benefits of BAV in adults typically do not last. The aortic valve becomes narrow again within months. [ 8 ] [ 1 ]  These patients may progress to more definitive treatment such as AVR or TAVI if they are eligible and clinically stable. [ 4 ] [ 1 ]  BAV in adults has risks and complications associated with it due to the risk of the procedure itself as well as the commonly high-risk patient population that undergoes BAV. Major bleeding,  stroke ,  aortic regurgitation , and death have been reported. [ 8 ]  Other complications reported include but are not limited to  infection , damage to the artery being accessed,  heart arrhythmias , and decreased  kidney function . [ 3 ] [ 1 ] [ 8 ]


It is typical for children to require reintervention after having BAV, whether it be a repeat BAV or more definitive treatment with surgical aortic valve replacement. [ 6 ]  Many do not require surgical aortic valve replacement until later on in life, with many patients reaching adulthood before this occurs. [ 9 ] [ 1 ]  The outcomes are worse for neonates and infants. This is largely because earlier intervention is required in these patients due to being less clinically stable. [ 1 ]  A common complication of BAV in children is  aortic regurgitation , which decreases in frequency the older the child is when the procedure occurs. [ 1 ]  Other complications include  arrhythmias , damage to the artery being accessed, as well as death. [ 1 ] [ 9 ]


For pregnant patients, data is lacking regarding outcomes of BAV. It is recommended that these patients requiring BAV progress to aortic valve replacement when suitable. Specific risks of performing BAV in pregnant patients include potential harm to the fetus from  radiation exposure . [ 2 ]


Apicoaortic Conduit (AAC) , also known as  Aortic Valve Bypass (AVB) , is a cardiothoracic surgical procedure that alleviates symptoms caused by blood flow obstruction from the  left ventricle  of the heart.  Left ventricular outflow tract obstruction (LVOTO) is caused by narrowing of the  aortic valve  ( aortic stenosis ) and other valve disorders.  AAC, or AVB, relieves the obstruction to blood flow by adding a bioprosthetic valve to the circulatory system to decrease the load on the aortic valve.  When an apicoaortic conduit is implanted, blood continues to flow from the heart through the aortic valve.  In addition, blood flow bypasses the native valve and exits the heart through the implanted valved conduit. The procedure is effective at relieving excessive pressure gradient across the natural valve. High pressure gradient across the aortic valve can be  congenital  or acquired. A reduction in pressure gradient results in relief of symptoms.


The figure depicts a typical apicoaortic configuration with a left ventricle connector sutured to the  apex of the heart , and a conduit containing a bioprosthetic valve  anastomosed  to the descending  thoracic aorta . Blood exits the  left ventricle  either through the natural valve or the bypass conduit. [ citation needed ]


The concept of an apicoaortic conduit to bypass valvular  aortic stenosis  (AS) was conceived by Carrel  [ 1 ]  in 1910, and performed experimentally by Sarnoff and colleagues on dogs in 1955. [ 2 ]  In 1962-63, Templeton implanted prostheses similar to those originally described by Sarnoff in five patients with severe aortic valve stenosis; one patient survived more than 10 years. In 1975, Bernhard and coworkers reported a reoperation in which a conduit was implanted between the left ventricle and the thoracic aorta. [ 3 ]  The procedure was also developed in the late 1970s as a way to treat complex left ventricular outflow tract obstructions (LVOTO) in children and young adults. [ 4 ]   [ 5 ]  AAC is no longer performed on children as the  Ross procedure  has superseded it. [ 6 ]


Today, AAC is performed clinically on elderly  aortic stenosis  patients, and has gained in popularity in recent years. In the past 25 years, a number of case series on adults have been published. [ 7 ]   [ 8 ]   [ 9 ]   [ 10 ]   [ 11 ]   [ 12 ]   [ 13 ]   [ 14 ]   [ 15 ]  As of 2010, the estimated total number of AAC cases performed worldwide in the last 30 years is greater than 1500. The procedure has not been adopted widely because it is technically challenging and blood loss can be significant. The most difficult part of the procedure is the insertion of a left ventricle connector into the  apex of the heart . [ citation needed ]


AAC requires specialized implants and installation tools. Hancock Laboratories, now part of Medtronic (Minneapolis, MN), developed and released a set of left ventricle connectors, valved conduits, and installation  trocars  in the 1970s. The Hancock left ventricle connectors, with inner diameters of 12 to 22 mm, have been used clinically for the vast majority of AAC procedures reported in the literature. For the valved conduit, surgeons have used the Medtronic Hancock Model 105 or 150 valved conduits which contain a complete porcine aortic valve. Other surgeons have constructed valved conduits on the back table using a variety of bioprosthetic valves such as the Medtronic Freestyle valve. The Hancock trocars for creating a hole in the left ventricle are rarely used clinically. Surgeons typically assemble their own tools to core and remove a plug of muscle from the left ventricular wall.


In 2011, Correx (Waltham, MA) [ 16 ]  released a complete kit for AVB with an installation tool that enables coring and insertion of a left ventricle connector on a beating heart while maintaining  hemostasis .  Cardiopulmonary bypass  (CPB) is not required. The kit is CE Marked and available in Europe. Several cases have been done in Canada under the Special Access Programme. [ 17 ]  This kit is not currently available for use or sale in the United States.


The general procedure has evolved over the years as surgeons gained experience and improved techniques.   [ 18 ]  A video of an AVB procedure performed by Dr. Jim Gammie of the University of Maryland Medical Center can be found here. [ 19 ]


The patient is placed on the table in the supine position. Anesthesia is induced, and the patient is intubated with a double-lumen endotracheal tube, which facilitates one-lung ventilation and allows the surgeon to work within the left chest. The patient is positioned with his or her left side up (see figure). A left anterior-lateral  thoracotomy  is performed between the fifth and sixth ribs to expose the heart and provide access to the  descending aorta . A portion of a rib may be removed to enable easier access and to minimize the chance of a rib fracture. The left lung is deflated and retracted. [ citation needed ]


With the descending aorta exposed, the surgeon applies a side clamp to the aorta, effectively pinching and isolating one side of the great vessel. Blood continues to flow to the body's lower half through the unisolated remainder of the aorta.  A lengthwise slit is made through the pinched face, and the open end of the valved conduit is carefully sutured to the slit. Once the suture line is checked for leaks, the aortic partial side clamp is removed and the valved conduit fills with blood up to the bioprosthetic valve. The valve acts as a check valve, thereby maintaining hemostasis.


The surgeon next opens the  pericardium  and exposes the  apex of the heart . The surgeon closely examines the surface of the heart and chooses and marks an insertion site near the apex. A ring of sutures reinforced with pledgets is installed around the insertion site. The free ends of the sutures are looped through a sewing ring on the left ventricle connector. At this point, CPB is typically initiated, although a few surgeons are able to complete the left ventricle installation off-pump (without CPB).
A circular core of  myocardium  is cut and removed using specialized coring tools. Care must be taken to avoid damaging structures inside the left ventricle such as the  interventricular septum , and the  chordae tendineae . The left ventricle connector is filled with sterile saline to displace any air and then inserted into the hole. The sutures are sequentially tightened and tied off to permanently secure the left ventricle connector to the apex. CPB is terminated. [ citation needed ]


With blood now flowing through the bypass conduit, the left ventricular outflow tract obstruction (LVOTO) is effectively relieved. 60% to 70% of the heart's output flows through the bypass to the aorta. The load on the heart is markedly reduced, and symptoms such as  dyspnea ,  syncope , and chest pain disappear.


Patients historically referred for apicoaortic conduit surgery have been considered high risk or ineligible for conventional  aortic valve replacement . The literature reports generally favorable outcomes for apicoaortic surgery given the age, frailty, and  comorbidities  of the patient population. Patients typically improve from  New York Heart Association Functional Classification  III or IV to Class I or II. AVB effectively relieves the LVOTO caused by  aortic stenosis .


There is long-term stability of the left ventricular  hemodynamics  after AVB, with no further biologic progression of native aortic valve stenosis.  Once the pressure gradient across the native valve is substantially reduced, the narrowing and calcification of the native valve halts. In one study of 47 patients whose average age was 82 years, the mean gradient across the native valve was reduced from 46 +/- 14 mm HG to 17 +/- 7 mm HG. [ 20 ]


Throughout the published literature, perioperative  stroke  is uncommon. This is because the native valve and ascending aorta are not manipulated in any way. Calcified layers and other debris do not break free and migrate to the brain. [ citation needed ]


The literature also reports that postoperative stroke is rare. Whenever a prosthetic device such as a valve is introduced into the bloodstream, there is an ongoing risk of  thrombus  formation which can lead to an  embolism  should the thrombus become mobile. Computational flow studies [ 21 ]  conclude that the presence of an aortic valve bypass conduit has no effect on cerebral blood flow. All blood flow to the brain continues to flow across the native valve. Should a thrombus form on the bioprosthetic valve in the bypass conduit, it will likely migrate to the lower half of the body and not to the brain. This fact is believed to reduce the long-term risk of cerebral thromboembolism (stroke) with AAC.


The published literature reports that the need for pacemaker after AAC is very rare as the (electrical) conduction center of the heart near the aortic valve is not disturbed in any way.


AAC avoids the risk of leakage around a replacement heart valve ( aortic insufficiency ), a serious complication of alternate treatments such as  aortic valve replacement  (AVR) and  percutaneous aortic valve replacement  (PAVR or TAVI). With AAC, the native aortic valve is left completely undisturbed. [ citation needed ]


With  aortic valve replacement  (AVR) as the accepted standard of care for critical AS, patients receiving apicoaortic conduits have often been refused AVR and as such are considered "no option" patients. AAC is also sometimes chosen by surgeons and cardiologists over other treatments, such as AVR and  percutaneous aortic valve replacement  (PAVR or TAVI), to treat critical AS. Patients who could benefit from AAC or AVB include those who: [ citation needed ]


Arterial switch operation  ( ASO ) or  arterial switch , is an  open heart   surgical  procedure used to correct  dextro-transposition of the great arteries  ( d-TGA ). [ 1 ] [ 2 ]


Its development was  pioneered  by  Canadian   cardiac  surgeon  William Mustard  and it was named for  Brazilian  cardiac surgeon  Adib Jatene , who was the first to use it successfully. It was the first method of d-TGA repair to be attempted, but the last to be put into regular use because of  technological  limitations at the time of its  conception .


Use of the arterial switch is  historically  preceded by two  atrial switch  methods: the  Senning  and  Mustard procedures . [ 3 ]


The atrial switch, which was an attempt to correct the physiology of transposition, had significant shortcomings that the arterial switch improved upon, in particular a reduced kinking of the  coronary arteries  when combined with the  LeCompte maneuver . The end result is that the aorta is repositioned behind the pulmonary arteries, functionally lengthening it and causing less angulation at the coronary origins. [ 4 ]


The Jatene procedure is ideally performed during the second week of life, before the  left ventricle  adjusts to the lower  pulmonary   pressure  and is therefore unable to support the  systemic circulation . [ 5 ]  In the event of  sepsis  or delayed  diagnosis , a combination of  pulmonary artery banding  ( PAB ) and  shunt  construction may be used to increase the left ventricular mass sufficiently to make an arterial switch possible later in  infancy . [ 6 ]


The success of ASO procedure is largely dependent on the facilities available, the skill and experience of the surgeon, and the general health of the  patient . Under preferable conditions, the  intra-operative  and  post-operative  success rate is 90% or more, with a comparable survival rate after 5 years. [ 7 ]  Approximately 10% of arterial switch recipients develop residual pulmonary  stenosis  post-operatively, which can lead to  right heart   failure  if left untreated; [ 8 ]  treatment usually involves  endovascular stenting  and/or  xenograft  patching. [ 7 ]


If the procedure is anticipated far enough in advance (with  prenatal  diagnosis, for example), and the individual's  blood  type is known, a family member with a compatible  blood type  may  donate  some or all of the blood needed for  transfusion  during the use of a  heart-lung machine  ( HLM ). The patient's  mother  is normally unable to donate blood for the transfusion, as she will not be able to donate blood during  pregnancy  (due to the needs of the  fetus ) or for a few weeks after giving  birth  (due to  blood loss ), and the process of collecting a sufficient amount of blood may take several weeks to a few months. However, in cases where the individual has been diagnosed but surgery must be delayed, maternal (or even  autologous , in certain cases) blood donation may be possible, as long as the mother has a compatible blood type. In most cases, though, the patient receives a donation from a  blood bank . A blood transfusion is necessary for the arterial switch because the HLM needs its "circulation" filled with blood and an infant does not have enough blood on their own to do this (in most cases, an adult would not require blood transfusion). [ citation needed ]


The patient will require a number of  imaging  procedures in order to determine the individual  anatomy  of the great arteries and, most importantly, the  coronary arteries . These may include  angiography ,  magnetic resonance imaging  ( MRI ), and/or  computed tomography  ( CT scan ). The coronary arteries are carefully mapped out in order to avoid unexpected intra-operative complications in transferring them from the native aorta to the neo-aorta. [ citation needed ]


As with any procedure requiring general anaesthesia, arterial switch recipients will need to  fast  for several hours prior to the surgery to avoid the risk of aspiration of vomitus during the induction of anesthesia. [ citation needed ]


As the patient is anesthetized, they may receive the following  drugs , which continue as necessary throughout the procedure:


The heart is accessed via  median sternotomy  and its  pericardium  is removed so the coronary and great arteries can be seen. The  ductus arteriosus  and main right  pulmonary artery , up to and including the first branches in the  hilum  of the right  lung , are separated from the surrounding supportive  tissue  to allow mobility of the  vessels . Cardiopulmonary bypass is then initiated and the  body  is  cooled  to prevent the  brain damage  otherwise associated with low blood flow during the surgery.


While the patient is cooling, the ductus arteriosus is  ligated  at both the aortic and pulmonary  ostia , then  transected  at its center; the main left pulmonary artery including its first branches in the left  hilum , is separated from surrounding connective tissue. When the patient is fully cooled, the ascending aorta is clamped and  cardioplegia  is achieved by delivering cold blood to the heart via the ascending aorta (below the  cross clamp ). The aorta and pulmonary arteries are  surgically cut . The vessels are again examined, and the pulmonary root is inspected for  left ventricular outflow tract obstruction . If a  ventricular septal defect  is present, it is also repaired via the  aortic  or  pulmonary valve .


The great arteries are usually arranged using the  LeCompte maneuver , with the aortic cross clamp positioned to hold the pulmonary artery  anterior  to the ascending aorta. On imaging, the pulmonary arteries will classically have the appearance of being draped over the aorta. Sometimes, however, patient anatomy prevents this and the aorta great vessels are kept in the non-anatomic 'anterior aorta' arrangement. The coronary arteries  infundibular  branches and the aortic root extending the  sinus of Valsalva  are then surgically cut off the native aorta and transplanted onto the pulmonary root to make a neo-aorta.


The bypass machine is then turned off, an  incision  is made in the right atrium, through which the  congenital  or  palliative   atrial septal defect  is repaired. In septal defects where a  Rashkind balloon atrial septostomy  was used, the ASD should be able to be closed with sutures, but cases involving large congenital atrial septal defects or  Blalock-Hanlon atrial septectomy , a patch can be used.


If there is a  ventricular septal defect  which has not yet been repaired, this is also fixed through the atrial incision and  tricuspid valve , again using sutures for a small defect or a patch for a large defect.


When the septal defects have been repaired and the atrial incision is closed, the patient is again placed on cardiopulmonary pass. The left ventricle is then vented and the cross clamp removed from the aorta, enabling full-flow to be re-established and rewarming to begin. At this point the patient will receive an additional dose of Regitine to keep  blood pressure  under control. The previously harvested pericardium is then used to patch the coronary  explantation  sites, and to extend and widen the neo-pulmonary root, which allows the pulmonary artery to be anastamosed without residua tension; the pulmonary artery is then transplanted to the neo-pulmonary root.


The patient is fitted with  chest tubes , temporary  pacemaker  leads, and  ventilated  before  weaning  from the HLM is begun.


The  rib cage  is relaxed and the external surgical  wound  is bandaged, but the  sternum  and chest incision are left open to provide extra room in the  pleural cavity , allowing the heart room to swell and preventing pressure caused by  pleural effusion .


The sternum and chest can usually be closed within a few days; however, the chest tubes, pacemaker, ventilator, and drugs may still be required after this time. The patient will continue to fast for up to a few days, and  breastmilk  or  infant formula  can then be gradually introduced via  nasogastric tube  ( NG tube ); the primary  goal  after a successful arterial switch, and before  hospital  discharge, is for the  infant  to gain back the weight they have lost and continue to gain weight at a normal or near-normal rate. [ citation needed ]


Scottish   pathologist   Matthew Baillie  first described  TGA  in 1797, presumably as a  posthumous  diagnosis. [ 9 ]  Without surgical correction, preoperative mortality in the neonate is approximately 30% within the first week of life and up to 90% within the first year; [ 7 ]  the survivors would have been those with one or more  concomitant   intracardiac   shunts  (ASD,  patent ductus arteriosus  ( PDA ),  patent foramen ovale  ( PFO ), and/or VSD), and are unlikely to have survived past  adolescence . [ 10 ]


In 1950,  American  surgeons  Alfred Blalock  and  C. Rollins Hanlon  introduced the  Blalock-Hanlon atrial septectomy , which was then routinely used to palliate patients. [ 11 ]  This would have effectively reduced early mortality rates, particularly in cases with no concomitant shunts, but is unlikely to have reduced late mortality rates.


Mustard first conceived of, and attempted, the anatomical repair (arterial switch) for d-TGA in the early 1950s. His few attempts were unsuccessful due to technical difficulties posed by the  translocation  of the coronary arteries, and the idea was abandoned. [ 12 ]


Swedish cardiac surgeon  Åke Senning  described the first corrective surgery for d-TGA (the  Senning procedure ) in 1959, which involved using the  atrial septum  to create an  intratrial   baffle  that redirected  bloodflow  at the  atrial  level; Senning yielded a high success rate using this procedure, significantly lowering both early and late mortality rates. [ 13 ]


Due to the technical complexity of the Senning procedure, others could not duplicate his success rate; in response, Mustard developed a simpler alternative method (the  Mustard procedure ) in 1964, which involved constructing a baffle from  autologous   pericardium  or  synthetic  material, such as Dacron. [ 14 ]  This procedure yielded early and late mortality rates comparable to the Senning procedure; however, a  late morbidity rate  was eventually discovered in relation to the use of synthetic graft material, which does not grow with the recipient and eventually causes  obstruction . [ 15 ]


In 1966, American surgeons  William Rashkind  and  William Miller  transformed the palliation of d-TGA patients with the innovative  Rashkind balloon atrial septostomy , which, unlike the  thoracotomy  required by a septectomy, is performed through the  minimally invasive  surgical technique of  cardiac catheterization . [ 16 ]


The late morbidity rate is  high in atrial switch, combined with advances in  microvascular surgery , created a renewed interest in Mustard's original concept of an arterial switch procedure. The first successful arterial switch was performed on a forty-two-day-old d-TGA + VSD infant by Jatene in 1975. [ 17 ]  Egyptian cardiac surgeon  Magdi Yacoub  was subsequently successful in treating TGA with AN intact  interventricular septum  when preceded by pulmonary artery banding and systemic-to-pulmonary shunt palliation. [ 6 ] [ 18 ]  Austrian surgeon  B. Eber  was the first to recount a small series of successful arterial switch procedures, and the first large successful series was reported by  Guatemalan  surgeon  Aldo R. Casteneda . [ 19 ]  In the postoperative period, increased incidence and degree of supravalvular pulmonary stenosis. [ 20 ]  Eliminating the pericardial patch for pulmonary artery reconstruction and using a direct connection reduced the incidence of this complication. [ 8 ] [ 21 ]


By 1991, the arterial switch had become the procedure of choice, and it remains the standard modern procedure for d-TGA repair. [ 7 ]


As long-term results of arterial switch are being reported, newer sets of potential surgical problems are becoming evident. Progressive neo-aortic dilation (pulmonary valve at birth) has been observed. However, this dilation does not necessarily translate into aortic regurgitation (AR) and need for surgery in all patients. Older age at time of ASO, presence of ventricular septal defect, and previous PA banding have been found to be risk factors for AR. [ 4 ] [ 22 ]   supravalvular pulmonary stenosis  was commonly observed in the postoperative period. A direct connection of the pulmonary artery reduced the incidence of this complication  [ 23 ] [ 24 ]


The world's smallest infant to survive an arterial switch was Jerrick De Leon, born 13 weeks premature. At the time of the operation on February 6, 2005, he weighed just over 1.5 pounds (700 grams). [ 25 ]


An  artificial heart valve  is a  one-way valve   implanted  into a person's  heart  to replace a  heart valve  that is not functioning properly ( valvular heart disease ). Artificial heart valves can be separated into three broad classes: mechanical heart valves, bioprosthetic tissue valves and engineered tissue valves.


The human heart contains four valves:  tricuspid valve ,  pulmonary valve ,  mitral valve  and  aortic valve . Their main purpose is to keep blood flowing in the proper direction through the heart, and from the heart into the major blood vessels connected to it (the  pulmonary artery  and the  aorta ). Heart valves can malfunction for a variety of reasons, which can impede the flow of blood through the valve ( stenosis ) and/or let blood flow backwards through the valve ( regurgitation ). Both processes put strain on the heart and may lead to serious problems, including  heart failure . While some dysfunctional valves can be treated with drugs or repaired, others need to be replaced with an artificial valve. [ 2 ]


A heart contains four valves (tricuspid, pulmonary, mitral and aortic valves) which open and close as blood passes through the heart. [ 3 ]  Blood enters the heart in the right atrium and passes through the  tricuspid valve  to the right ventricle. From there, blood is pumped through the  pulmonary valve  to enter the lungs. After being oxygenated, blood passes to the left atrium, where is it pumped through the  mitral valve  to the left ventricle. The left ventricle pumps blood to the aorta through the  aortic valve .


There are many potential causes of heart valve damage, such as birth defects, age related changes, and effects from other disorders, such as rheumatic fever and infections causing  endocarditis .  High blood pressure  and heart failure which can enlarge the heart and arteries, and scar tissue can form after a  heart attack  or injury. [ 4 ]


The three main types of artificial heart valves are mechanical, biological (bioprosthetic/tissue), and tissue-engineered valves. In the US, UK and the European Union, the most common type of artificial heart valve is the bioprosthetic valve. Mechanical valves are more commonly used in Asia and Latin America. [ citation needed ]  Companies that manufacture heart valves include Edwards Lifesciences, [ 5 ]  Medtronic, [ 6 ]  Abbott (St. Jude Medical), [ 7 ]  CryoLife, [ 8 ]  and LifeNet Health. [ 9 ]


Mechanical valves come in three main types – caged ball, tilting-disc and bileaflet – with various modifications on these designs. [ 10 ]  Caged ball valves are no longer implanted. [ 11 ]  Bileaflet valves are the most common type of mechanical valve implanted in patients today. [ 12 ]


The first artificial heart valve was the caged ball valve, a type of  ball check valve , in which a ball is housed inside a cage. When the heart contracts and the blood pressure in the chamber of the heart exceeds the pressure on the outside of the chamber, the ball is pushed against the cage and allows blood to flow. When the heart finishes contracting, the pressure inside the chamber drops and the ball moves back against the base of the valve forming a seal.


In 1952,  Charles A. Hufnagel  implanted caged ball heart valves into ten patients (six of whom survived the operation), marking the first success in prosthetic heart valves. [ citation needed ]  A similar valve was invented by Miles 'Lowell' Edwards and  Albert Starr  in 1960, commonly referred to as the Starr-Edwards silastic ball valve. [ 13 ]  This consisted of a silicone ball enclosed in a  methyl metacrylate  cage welded to a ring. The Starr-Edwards valve was first implanted in a human on August 25, 1960, and was discontinued by Edwards Lifesciences in 2007. [ 13 ]


Caged ball valves are strongly associated with blood clot formation, so people who have one required a high degree of  anticoagulation , usually with a target  INR  of 3.0–4.5. [ 14 ]


Introduced in 1969, the first clinically available tilting-disc valve was the  Bjork-Shiley valve . [ 15 ]  Tilting‑disc valves, a type of  swing check valve , are made of a metal ring covered by an  ePTFE  fabric. The metal ring holds, by means of two metal supports, a disc that opens when the heart beats to let blood flow through, then closes again to prevent blood flowing backwards. The disc is usually made of an extremely hard carbon material ( pyrolytic carbon ), enabling the valve to function for years without wearing out. [ citation needed ]


Introduced in 1979, bileaflet valves are made of two semicircular leaflets that revolve around struts attached to the valve housing. With a larger opening than caged ball or tilting-disc valves, they carry a lower risk of blood clots. They are, however, vulnerable to blood backflow. [ citation needed ]


The major advantage of mechanical valves over bioprosthetic valves is their greater durability. [ 16 ]  Made from metal and/or  pyrolytic carbon , [ 10 ]  they can last 20–30 years. [ 16 ]


One of the major drawbacks of mechanical heart valves is that they are associated with an increased risk of  blood clots . Clots formed by red blood cell and platelet damage can block blood vessels leading to  stroke . People with mechanical valves need to take anticoagulants (blood thinners), such as  warfarin , for the rest of their life. [ 16 ]  Mechanical heart valves can also cause  mechanical hemolytic anemia , a condition where the  red blood cells  are damaged as they pass through the valve. [ citation needed ]   Cavitation , the rapid formation of microbubbles in a fluid such as blood due to a localized drop of pressure, can lead to mechanical heart valve failure, [ 17 ]  so cavitation testing is an essential part of the valve design verification process.


Many of the complications associated with mechanical heart valves can be explained through  fluid mechanics . For example, blood clot formation is a side effect of high  shear stresses  created by the design of the valves. From an engineering perspective, an ideal heart valve would produce minimal pressure drops, have small regurgitation volumes, minimize turbulence, reduce prevalence of high stresses, and not create flow separations in the vicinity of the valve. [ citation needed ]


Implanted mechanical valves can cause foreign body rejection. The blood may coagulate and eventually result in a hemostasis. The usage of anticoagulation drugs will be interminable to prevent thrombosis. [ 18 ] [ non-primary source needed ]


Bioprosthetic valves are usually made from animal tissue (heterograft/ xenograft ) attached to a metal or polymer support. [ 11 ]  Bovine (cow) tissue is most commonly used, but some are made from porcine (pig) tissue. [ 19 ] [ non-primary source needed ]  The tissue is treated to prevent rejection and  calcification . [ citation needed ]


Alternatives to animal tissue valves are sometimes used, where valves are used from human donors, as in aortic  homografts  and pulmonary  autografts . An aortic homograft is an aortic valve from a human donor, retrieved either after their death or from a heart that is removed to be replaced during a heart transplant. [ 12 ]  A pulmonary autograft, also known as the  Ross procedure , is where the aortic valve is removed and replaced with the patient's own  pulmonary valve  (the valve between the right ventricle and the pulmonary artery). A pulmonary homograft (a pulmonary valve taken from a cadaver) is then used to replace the patient's own pulmonary valve. This procedure was first performed in 1967 and is used primarily in children, as it allows the patient's own pulmonary valve (now in the aortic position) to grow with the child. [ 12 ]


Bioprosthetic valves are less likely than mechanical valves to cause blood clots, so do not require lifelong anticoagulation. As a result, people with bioprosthetic valves have a lower risk of bleeding than those with mechanical valves. [ 16 ]


Tissue valves are less durable than mechanical valves, typically lasting 10–20 years. [ 20 ]   This means that people with bioprosthetic valves have a higher incidence of requiring another aortic valve replacement in their lifetime. [ 16 ]  Bioprosthetic valves tend to deteriorate more quickly in younger patients. [ 21 ]


In recent years, scientists have developed a new tissue preservation technology, with the aim of improving the durability of bioprosthetic valves. In sheep and rabbit studies, tissue preserved using this new technology had less  calcification  than control tissue. [ 22 ]  A valve containing this tissue is now marketed, but long-term durability data in patients are not yet available. [ 23 ] [ non-primary source needed ]


Current bioprosthetic valves lack longevity, and will calcify over time. [ 24 ]  When a valve calcifies, the valve cusps become stiff and thick and cannot close completely. [ 24 ]  Moreover, bioprosthetic valves can't grow with or adapt to the patient: if a child has bioprosthetic valves they will need to get the valves replaced several times to fit their physical growth. [ 24 ]


For over 30 years researchers have been trying to grow heart valves  in vitro . [ 25 ]  These tissue‑engineered valves involve seeding human cells on to a scaffold. [ 25 ]  The two main types of scaffold are natural scaffolds, such as decellularized tissue, or scaffolds made from degradable polymers. [ 26 ]  The scaffold acts as an  extracellular matrix , guiding tissue growth into the correct 3D structure of the heart valve. [ 26 ] [ 25 ]  Some tissue-engineered heart valves have been tested in clinical trials, [ 26 ]  but none are commercially available.


Tissue engineered heart valves can be person-specific and 3D modeled to fit an individual recipient [ 27 ]  3D printing is used because of its high accuracy and precision of dealing with different biomaterials. [ 27 ]  Cells that are used for tissue engineered heart valves are expected to secrete the extracellular matrix (ECM). [ 24 ]  Extracellular matrix provides support to maintain the shape of the valves and determines the cell activities. [ 28 ]


Scientists can follow the structure of heart valves to produce something that looks similar to them, but since tissue engineered valves lack the natural cellular basis, they either fail to perform their functions like natural heart valves, or function when they are implanted but gradually degrade over time. [ citation needed ]  An ideal tissue engineered heart valve would be non-thrombogenic, biocompatible, durable, resistant to calcification, grow with the surrounding heart, and exhibit a physiological hemodynamic profile. [ 29 ]  To achieve these goals, the scaffold should be carefully chosen—there are three main candidates: decellularized ECM (xenografts or homografts), natural polymers, and synthetic polymers. [ 29 ]


Mechanical and tissue valves are made of different materials. Mechanical valves are generally made of titanium and carbon. [ 30 ]  Tissue valves are made up of human or animal tissue. The valves composed of human tissue, known as allografts or homografts, are from donors' human hearts. [ 30 ]


Mechanical valves can be a better choice for younger people and people at risk of valve deterioration due to its durability. It is also preferable for people who are already taking blood thinners and people who would be unlikely to tolerate another valve replacement operation. [ citation needed ]


Tissue valves are better for older age groups as another valve replacement operation may not be needed in their lifetime. Due to the risk of forming blood clots for mechanical valves and severe bleeding as a major side effect of taking blood-thinning medications, people who have a risk of blood bleeding and are not willing to take warfarin may also consider tissue valves. Other patients who may be more suitable for tissue valves are people who have other planned surgeries and unable to take blood-thinning medications. People who plan to become pregnant may also consider tissue valves as warfarin causes risks in pregnancy. [ citation needed ]


An artificial heart valve should ideally function like a natural heart valve. [ 11 ]  The functioning of natural heart valves is characterized by many advantages:


The performance of an artificial heart valve can be tested  in vitro  before clinical use by means of a  pulse duplicator . [ 32 ]


Artificial heart valves are expected to last from 10 to 30 years. [ 16 ]


The most common problems with artificial heart valves are various forms of degeneration, including gross billowing of leaflets, ischemic mitral valve pathology, and minor chordal lengthening. [ 24 ]  The repairing process of the artificial heart valve regurgitation and stenosis usually requires an open-heart surgery, and a repair or partial replacement of regurgitant valves is usually preferred. [ 24 ]


Researchers are investigating catheter-based surgery that allows repair of an artificial heart valve without large incisions. [ 33 ]


Researchers are investigating Interchangeable Prosthetic Heart Valve that allows redo and fast-track repair of an artificial heart valve.  [ 34 ]


Atrial septostomy  is a  surgical procedure  in which a small hole is created between the upper two chambers of the  heart , the  atria . This procedure is primarily used to palliate  dextro-Transposition of the great arteries  or d-TGA (often imprecisely called  transposition of the great arteries ), a life-threatening  cyanotic   congenital heart defect  seen in infants. It is performed prior to an  arterial switch operation . Atrial septostomy has also seen limited use as a surgical treatment for  pulmonary hypertension . [ 1 ]  The first atrial septostomy (then less precisely called a septectomy) was developed by  Vivien Thomas  in a canine model and performed in humans by  Alfred Blalock . The Rashkind balloon procedure, a common atrial septostomy technique, was developed in 1966 by American cardiologist  William Rashkind  at the  Children's Hospital of Philadelphia .


There are two types of this procedure:  balloon atrial septostomy  (also called  endovascular atrial septostomy ,  Rashkind atrial balloon septostomy , or simply  Rashkind's procedure ) and  blade atrial septostomy  (also called  static balloon atrial septostomy ).


In a normal  heart ,  oxygen -depleted blood ("blue") is pumped from the  right side of the heart , through the  pulmonary artery , to the  lungs  where it is oxygenated. This is the  pulmonary circulation  part of blood flow. The oxygen-rich ("red") blood then returns to the  left heart , via the  pulmonary veins , and is pumped through the  aorta  to the rest of the body, including the heart  muscle  itself. This is the  systemic circulation  part of blood flow, the other loop of an interconnected normal  cardio - pulmonary  system. [ citation needed ]


With d-TGA, certain major blood vessels are connected improperly, so oxygen-poor blood from the right heart is pumped immediately through the aorta and circulated to the body and the heart itself, bypassing the lungs altogether, while the left heart pumps oxygen-rich blood continuously back into the lungs through the pulmonary artery. This is a life-threatening situation due to the resultant  low oxygen levels  throughout the body. Atrial septostomy allows more of the oxygen-rich blood to circulate throughout the body. The procedure is a temporary measure meant to help the patient survive until further corrective surgery can be done.


In the separate case of pulmonary hypertension, abnormally high blood pressure in the blood vessels within and connected to the lungs puts stress on the right side of the heart, potentially leading to  right heart failure . Atrial septostomy relieves some of this pressure, but at the cost of lower oxygen levels in the blood ( hypoxia ). As with d-TGA, this surgery is not a definitive solution to the underlying medical problem. [ 2 ]


The majority of atrial septostomies are performed on infants with d-TGA or other  cyanotic heart defects . In these cases, a  balloon catheter  is guided through a large  vein  into the  right atrium , during  cardiac catheterization . The catheter is threaded into the  foramen ovale , a naturally existing hole between the atria that normally closes shortly after birth. The balloon at the end of the catheter is inflated so as to enlarge the foramen ovale enough that it will no longer become sealed. This allows more oxygenated blood to enter the  right heart  (especially in the case of d-TGA) where it can be pumped to the rest of the body. The balloon is deflated and the catheter is removed. [ citation needed ]


Sometimes the initial surgery is not entirely successful, or there are other factors that make a simple balloon atrial septostomy impossible, such as an older patient whose foramen ovale has already closed. This is when a blade atrial septostomy is performed. The details of the procedure are largely the same, except that a small blade on the end of the  catheter  is first used to create an opening between the right and left atria, before the insertion of the balloon.


The Rashkind balloon atrial septostomy is performed during  cardiac catheterization  (heart cath), in which a  balloon catheter  is used to enlarge a  foramen ovale ,  patent foramen ovale  (PFO), or  atrial septal defect  (ASD) in order to increase  oxygen saturation  in patients with  cyanotic   congenital   heart defects  (CHDs). It was developed in 1966 by  American   surgeons   William Rashkind  and  William Miller  at the  Children's Hospital of Philadelphia .


William Rashkind was not a surgeon, but a pediatric cardiologist at the Children's Hospital of Philadelphia.  He was one of the fathers of the field of interventional catheterization, and he developed not only this life-saving technique and device for neonates with transposition of the great arteries, but also devices to close atrial septal defects (ASDs) and persistent patent ductus arteriosus (PDA).  He was the chief of the Division of Pediatric Cardiology at the Children's Hospital of Philadelphia until his death in 1986 from malignant melanoma.


As with any surgery, there are certain risks to atrial septostomy, including tearing of the cardiac tissue,  arrhythmias , and rarely, death.


Atrial switch  is a  heart operation  performed to treat  dextro-Transposition of the great arteries . [ 1 ] [ 2 ]  It involves the construction of an atrial baffle which redirects the blood coming into the atria to restore the connection between systemic and pulmonary circulation. [ 3 ]


Two variants of the atrial switch operation developed – the  Senning procedure  (1950s) which uses the patient's own tissue ( pericardium ) to construct the baffle, and the  Mustard procedure  (1960s), which uses a synthetic material. [ 4 ]  It has largely been replaced by the  arterial switch operation . [ 4 ]  The operation is more commonly performed in developing countries, where the condition frequently presents late. [ 5 ]


Bakulev Scientific Center for Cardiovascular Surgery  ( Russian :  Научный центр сердечно-сосудистой хирургии им. А.Н. Бакулева ) is attached to the  Russian Academy of Medical Sciences  and is one of the leading  cardiovascular surgery -related facilities of the  Russian Federation . The center consists of  Burakovskiy Institute of Cardiac Surgery  and the Institute of Coronary and Vascular Surgery, both located in  Moscow , as wells as it has a filial branch in  Perm  - Perm Heart Institute. In 2005 the Center started the first phase of research into the transplant of  marrow cells  in patients with  acute myocardial infarction . [ 1 ]


The Center was founded in 1956 by  Soviet  surgeon  Aleksandr Bakulev , being officially named the Thoracal Surgery Institute of the Academy of Medical Sciences of the USSR (Институт грудной хирургии Академии медицинских наук СССР) at the time. In 1961 the facility was renamed to the Institute of Cardiovascular Surgery and in 1967, following Bakulev's death, gained his name. [ citation needed ]


The network community  Dissernet  has pointed out that the Center has repeatedly (>45 cases) awarded the Ph.D level degrees based on heavily plagiarised and sometimes falsified theses. [ 2 ]


55°45′42″N   37°22′36″E  /  55.76167°N 37.37667°E  /  55.76167; 37.37667


Balloon septostomy  is the widening of a  foramen ovale ,  patent foramen ovale  ( PFO ), or  atrial septal defect  ( ASD ) via  cardiac catheterization  ( heart cath ) using a  balloon catheter . This procedure allows a greater amount of  oxygenated   blood  to enter the  systemic circulation  in some cases of  cyanotic   congenital   heart defect  ( CHD ). [ citation needed ]


After the catheter is inserted, the deflated balloon catheter is passed from the  right atrium  through the foramen ovale, PFO or ASD into the left atrium, it is then  inflated  and pulled back through to the right atrium, thereby enlarging the opening and allowing greater amounts of blood to pass through it. The resulting man-made opening is one of many forms of  shunting , and is often referred to as an ASD.


This is normally a  palliative  procedure used to prepare a patient for, or sustain them until, a  corrective surgery  can be performed. At this time the ASD is closed using either  sutures  or a  cardiac patch , depending on the size and/or nature of the opening. The procedure is often unsuccessful in infants and children older than one month because of a thickened septum. [ 1 ]


Dhaniram Baruah  is an Indian  heart surgeon  from Assam, known for his work in the field of  xenotransplantation . He is popularly known as India's  Pig Heart Doctor . [ 1 ]  On 1 January 1997, he became the first heart surgeon in the world to transplant a pig's heart in a human body. [ 2 ]  Although the recipient died subsequently, it was a precursor to the first successful pig-to-human heart transplant performed 25 years later by  Bartley P. Griffith  in January 2022. [ 3 ]  While Griffith used a genetically modified pig's heart, Barua had transplanted a normal pig heart. [ 4 ]  Barua is also the founder of Dr Dhaniram Baruah Heart Institute & Research Centre. [ 5 ]  He can only communicate through hand gestures after a  brain stroke  left him unable to speak. [ 6 ]


Throughout his career Barua has courted controversies due to his maverick ideas and unconventional methods. [ 7 ]  The pig heart transplanted by Barua in his patient Purna Saikia worked for seven days, after which due to implications of infections, and the transplant was rejected by the recipient's body. Barua was sent to jail for 40 days in 1997 for negligence and violation of medical ethics. His clinic and research center was burnt down by an angry mob. He was also called a mad man and ostracised from the local community. But undeterred he continued his experiments, and claimed that successful transplantation of a pig heart in a human body was feasible. He later claimed damages from the Government for his humiliation and unjust treatment. [ 8 ]  He also claimed to have found a cure for HIV/AIDS. [ 9 ] [ 10 ] [ 11 ]


Barua claims to have cured 86 patients of HIV/AIDS for which no conventional medicine is available. [ 12 ]  He has written a two-volume book titled "AIDS Reaching the Unreachable with Baruah Combat Genes". [ 13 ]


The  Batista procedure  (also called a reduction left ventriculoplasty) was an experimental heart procedure that proposed the reversal of the effects of remodeling in cases of end-stage  dilated cardiomyopathy  refractory to conventional medical therapy. The hypothesis of the operation appears to be that reduction (resection) of marginally viable ventricular mass may result in superior geometric remodeling thus conferring better performance when faced with ventricular failure. In spite of promising initial results, the method was soon found to be of little if any benefit, and it is no longer considered a recommended treatment for the disease.


The Batista procedure was invented by Brazilian physician and cardiac surgeon  Randas Batista  in 1994 for use in patients with non-ischemic  dilated cardiomyopathy . Many of his patients were victims of  Chagas disease . Chagas disease represents a parasitic nonischemic cardiomyopathy targeting parasympathetic inflow to the heart. Chagas cardiomyopathy thus represents a unique method of study of diastolic heart failure. It may be addressed by removal of a portion of viable tissue from the left ventricle to reduce its size (partial left ventriculectomy), with or without repair or replacement of the mitral valve. [ 1 ]


Although several studies showed benefits from this surgery, studies at the  Cleveland Clinic  concluded that this procedure was associated with a high early and late failure rate. At 3 years only 26 percent were event-free and survival rate was only 60 percent. [ 2 ]  Most hospitals in the US have abandoned this operation and it is no longer included in heart failure guidelines. [ 3 ] [ 4 ]


The  Bentall procedure  is a type of  cardiac surgery  involving composite graft replacement of the  aortic valve ,  aortic root , and  ascending aorta , with re-implantation of the  coronary arteries  into the graft.  This operation is used to treat combined disease of the aortic valve and ascending aorta, including lesions associated with  Marfan syndrome .  The Bentall procedure was first described in 1968 by  Hugh Bentall  and Antony De Bono. [ 1 ]  It is considered a standard for individuals who require aortic root replacement, and the vast majority of individuals who undergo the surgery receive  mechanical valves . [ 2 ] [ 3 ]


Since its inception, the Bentall procedure has been considered a gold standard of aortic valve replacement.


Importantly, the use of mechanical vs biologic valves are not predictive of quality of life overall, morbidity and mortality. [ 5 ] [ 6 ]  General guidelines for the repair of valvular heart disease indicate the medical team takes into consideration the following patient factors for the determination of best conduit to use: age, life expectancy, lifestyle choices (diet, exercise, hobbies, risk of potential falls/ physical trauma), medical history (history of stroke or blood clots), likelihood of surgical or transcatheter repeat procedure, and of course patient preference.


The Bentall procedure is considered for patients who may have Marfan syndrome, aortic dissection, aortic root aneurysm, aortic regurgitation of the valve. calcification of the aortic valve, and congenital anomalies. [ 1 ] [ 7 ]


Early Morbidity and Mortality
Within 30 days of hospitalization, morbidity and mortality after Bentall procedure are associated with complications stemming from  cardiac arrhythmia ,  pneumonia ,  acute respiratory distress syndrome (ARDS) ,  sepsis , graft infection, wound infection, neurologic/ cerebrovascular accident and  stroke , hemorrhage/ bleeding,  myocardial infarction ,  pericardial effusion , organ damage/ deterioration. [ 8 ]  Overall, these complications are seen in < 6% of patients undergoing this procedure, with risk of complications being greatly associated with other preexisting risk factors and comorbidities. [ 3 ] [ 8 ]


Like early morbidity and mortality, infection of a graft after Bentall Procedure is rare affecting < 5% of cases, but can be of very serious consequence to the patient. [ 8 ] [ 9 ]  Many of these patients who develop infections have multiple comorbidities and risk factors existing before the surgery including diabetes, suppression of the immune system, preexisting cardiovascular issues outside of the direct indication for a Bentall procedure and cancer. [ 7 ]


Graft infection from a Bentall procedure presents similarly to many infections after a major cardiac surgery, with indications in various degrees of severity. Symptoms can include fever, chills, loss of appetite, weight loss, malaise with clinical indications including septic emboli, abscess, left ventricular fistulae, transient ischemic attack. [ 7 ] [ 9 ]  These can occur weeks to years after the Bentall procedure itself.


If a patient is suspected to have a graft infection, they should immediately seek medical attention. Evaluation of an infection may include blood work including  CBC ,  CMP ,  blood cultures . Further assessment and imaging may involve  transesophageal echocardiography ,  CT scan ,  CT Angiography ,  PET scan . [ 9 ] [ 10 ]  Depending on the modality, evidence of infection includes: increased glucose uptake,  pseudoaneurysm , fistula, fluid/ attenuation around the graft (indicating increased inflammation), or other increased signs of inflammation around the graft; these findings are then taken into account and assessed in the context of the clinical/ symptomatic picture of the patient. [ 10 ]


If a graft infection is highly likely, treatment involves admission to a hospital setting and administration of IV antibiotics. If the infection does not resolve, a graft infection may eventually require either an attempt at graft salvage or a revision surgery for the removal of the infected graft. [ 10 ]


Valve sparing aortic root replacement (VSARR)  is an alternative procedure to the composite aortic valve graft (CAGVR, Bentall procedure). A notable benefit of VSARR is the reduced need for anticoagulation, as the patient's own aortic valve is spared and does not need to be replaced with a mechanical or bioprosthetic valve. [ 11 ]


The VSARR is relatively new compared to the Bentall procedure and is performed about two thirds less often, associated with the increased skill and learning curve needed to navigate the procedure. [ 11 ]  Additionally, literature overall has shown unclear longevity and longitudinal patient outcomes compared to the Bentall procedure. Recently, there is some evidence VSARR has superior survival rates at 10 and 15 years along with reduced early mortality. [ 11 ]  Moreover, while there is a decreased reoperation rate in the first 5 years seen with the Bentall procedure, the need for reoperation after Bentall and VSARR are then comparable thereafter. [ 11 ]


Vocabulary:


Endovascular procedures have been gaining popularity, especially within the last decade, due to their faster healing times and often lower risk of complications. The creation of the Endo-Bentall device showcases a Bentall procedure, but performed in a minimally invasive setting. [ 13 ]  This is an option for high risk patients otherwise not a candidate for a traditional open procedure. The Endo-Bentall device is made up of three parts: a self-expanding  transcatheter aortic valve (TAVR)  +  aortic endovascular stent graft (TEVAR)  and wire-reinforced fenestrations. [ 13 ]  Candidacy of this procedure is determined by an interdisciplinary team which may include cardiac and vascular surgeons, as well as interventional cardiologists. [ 14 ]


There are several limitations of using the Endo-Bentall, including: incorporating coronary arteries, modifying TAVR devices to be better suited for treating aortic valve insufficiency and regurgitation, and addressing a need for dedicated bridging stents. [ 15 ]


Beyond the Endo-Bentall, modern literature points to some promising future directions for the repair of the ascending aorta and aortic arch, including: steerable device delivery sheaths, dedicated bridging stents, grafts that can adjust for deployability/ improved positioning, grafts with better anti-embolic protection, left ventricle wires that minimize trauma to the heart, and fusion imaging optimization. [ 15 ]


The  Blalock–Hanlon procedure  was created by Alfred Blalock and C. Rollins Hanlon. It was described in 1950. [ 1 ]  Alfred Blalock was an American surgeon most known for his work on the Blue Baby syndrome. [ 2 ]  C. Rollins Hanlon was also an American surgeon but was best known for his work in cardiology. [ 3 ]  The procedure that these two men created, known as the Blalock–Hanlon procedure, was a new concept termed atrial septectomy. This procedure had been experimented on the right atrium of dogs before Dr. Blalock and Dr. Hanlon had performed it on humans. [ 4 ]


It involves the intentional creation of a septal defect in order to alter the flow of oxygenated blood.  It was devised as a palliative correction for  transposition of the great vessels .


The Blalock–Hanlon procedure was a cardiothoracic procedure created in the 1950s. The Blalock–Hanlon procedure was created to enhance intracardiac combinations. [ 5 ]  A majority of the surgeries using this procedure were performed in pediatrics on infants ranging from one day to five months of age. [ 5 ]  Of all the children who had this surgery, only one had to undergo a second operation to repair damage not fixed during the Blalock–Hanlon procedure. [ 6 ]  According to Behrendt, Orringer, and Stern, there were only ten early deaths out of the forty-eight children the operation was performed on. [ 5 ]  The deaths were of children that were less than one month old due to extensive measures taken during the operation. [ 5 ]


The procedure also had a relatively high mortality rate of only twenty-one percent while it was performed however, because of the excessive mortality rate it is no longer used in today's medical society. [ 5 ]  This procedure was a combination of two circulations (Pulmonary and Systematic). [ 4 ]  Due to the intracardiac mixing, the procedure can cause postoperative arrhythmias, cerebral thrombosis, adhesions develops in the pericardial space, and many infants will face death between the septectomy. [ 5 ]


The  Blalock–Thomas–Taussig shunt  ( BTT shunt ), [ 1 ]  previously known as the  Blalock–Taussig Shunt  ( BT shunt ), [ 2 ]  is a surgical procedure used to increase blood flow to the lungs in some forms of  congenital heart disease [ 3 ]  such as  pulmonary atresia  and  tetralogy of Fallot , which are common causes of  blue baby syndrome . [ 3 ]  The procedure involves connecting a branch of the  subclavian artery  or  carotid artery  to the  pulmonary artery . In modern practice, this procedure is temporarily used to direct blood flow to the lungs and relieve cyanosis while the infant is waiting for corrective or definitive surgery when their heart is larger. The BTT shunt is used in the first step of the three-stage palliation (the  Norwood procedure ).


While the originally described Blalock–Thomas–Taussig shunt directly connected the subclavian and pulmonary arteries, in contemporary practice a modified version of the procedure, the mBTT shunt, is more commonly used. [ 2 ] [ 4 ]  In the modified Blalock–Thomas–Taussig shunt, a length of artificial tubing typically made from  PTFE  ( Gore-tex ) is sewn between either the subclavian or the carotid artery and the corresponding side branch of the pulmonary artery. [ 4 ]  This modification removes the need to cut off blood supply and makes it easier to regulate the blood flow to the lungs. Some centers now use a shunt directly from the right ventricle to the pulmonary artery, a  Sano shunt . This is done to avoid the reduced diastolic blood flow in the  coronary circulation  associated with the mBTT shunt. [ citation needed ]


The original procedure was named for  Alfred Blalock , surgeon, Culloden, GA (1899–1964),  Helen B. Taussig , cardiologist, Baltimore/Boston (1898–1986) and  Vivien Thomas  (1910–1985) who was at that time Blalock's laboratory assistant. They all helped to develop the procedure. Taussig, who treated hundreds of infants and children with this disorder, had observed that children with a cyanotic heart defect and a  patent ductus arteriosus  (PDA) lived longer than those without the PDA. It, therefore, seemed to her that a shunt that mimicked the function of a PDA might relieve the tetralogy patients' poor oxygenation. In 1943, having broached the possibility of a surgical solution to  Robert Gross  of Boston without success, Taussig approached Blalock and Thomas in their Hopkins laboratory in 1943. According to the account of the original consultation between the three provided in Vivien Thomas' 1985 autobiography  Partners of the Heart , Taussig carefully described the anomaly of Tetralogy of Fallot, but made no suggestion about the specific surgical correction required, observing merely that it should be possible to get more blood to the lungs, "as a plumber changes pipes around."  Although Taussig was not aware of it at that time, Blalock and Thomas had already experimented with such an  anastomosis , one that Blalock had conceived years earlier for a different purpose but which had the unanticipated effect of re-routing blood to the lungs. The operation involved the joining of the subclavian artery to the pulmonary artery. After meeting with Taussig, the two men set about perfecting the operation in the animal lab, with Thomas performing the subclavian-to-pulmonary anastomosis alone in some 200 laboratory dogs, then adapting the instruments for the first human surgery from those used on the experimental animals and coaching Blalock through the first 100 operations on infants. [ citation needed ]


Thomas' autobiographical account, corroborated by the participants in the early tetralogy operations ( Denton Cooley  and the late William P. Longmire, Jr., intern and resident respectively during the surgery) has led to the recent conclusion that Thomas' contribution, both experimentally and clinically, was so critical that he should have received credit for the procedure along with Blalock and Taussig. However, because of the racial prejudices of the time, and the academic custom which generally precluded mention of non-degreed lab assistants (Thomas had no formal education beyond high school), he did not receive the honor of having the shunt named after him. The 2004 HBO television movie  Something the Lord Made , based on  Washingtonian  writer Katie McCabe's 1989 article of the same name, was made about his role in the historic Blue Baby surgery, as was the 2003 public television documentary  Partners of the Heart. [ citation needed ]


Cardiomyoplasty  is a surgical procedure in which healthy  muscle  from another part of the body is wrapped around the  heart  to provide support for the failing heart. [ 1 ]  Most often the  latissimus dorsi muscle  is used for this purpose. A special pacemaker is implanted to make the skeletal muscle contract. If cardiomyoplasty is successful and increased cardiac output is achieved, it usually acts as a bridging therapy, giving time for damaged  myocardium  to be treated in other ways, such as remodeling by cellular therapies. [ 2 ] [ 3 ]


Cellular cardiomyoplasty  is a method which augments myocardial function and cardiac output by directly growing new muscle cells in the damaged myocardium (heart muscle). Tissue engineering, which is now being categorized as a form of regenerative medicine, can be defined as biomedical engineering to reconstruct, repair, and improve biological tissues. Research efforts in tissue engineering have been ongoing and it is emerging as one of the key areas of medical research. Furthermore, there are vast developments in tissue engineering, which involve leveraging of technologies from biomaterials, molecular medicine, biochemistry, nanotechnology, genetic and biomedical engineering for regeneration and cell expansion targets to restructure and/or repair human organs. Injection of cardiomyogenic and/or angiogenic stem cells have been proposed as alternatives to existing treatments. For cardiovascular application, skeletal myoblasts are of great interest as they can be easily isolated and are associated with high proliferation rate. These cells have also been demonstrated to be  hypoxia -resistant.


Bone marrow contains different cell populations, which exhibit excellent plasticity toward cardiogenic and endothelial cells. These cell populations are endothelial progenitor cells, hematopoietic stem cells and mesenchymal stem cells.  Adipose tissue host progenitor cells with reported interesting cardiomyogenic and vasculogenic potential in the sense that they improve heart functions and reduce infarction size in rodent animal models.  Subcutaneous adipose tissue is also a source of mesenchymal stem cells and have demonstrated positive outcomes in terms of cardiovascular tissue remodeling. Mammal hearts also host naturally occurring cardiac stem cells which may be capable of differentiating themselves into cardiomyocytes, endothelial cells and cardiac fibroblasts. [ 4 ]  This self-regeneration capacity gives rise to alternatives to classical cellular therapies whereby administration of growth factors such as Thymosin β4 for cell activation and migration are solely necessary. Largely democratized in terms of population information, embryonic stem cells are known for their strong capacity for expansion and differentiation into cardiomyocytes, endothelial cells and cardiac fibroblasts.


However, if non autologous, immunosuppression therapy is associated with such treatment. Hence, research has been focused on induced pluripotent stem cells (iPSCs) from somatic human tissue. Further to cell and necessary relevant growth factor selection, cell delivery is an important issue.  Indeed, the intracoronary route is the most straightforward cell delivery route as associated with intramyocardial cellular retention; retention rates are however low, i.e. exceed 10%. Washed off cells reach other organs or die, which can be an issue at the time of prepare ICH module 8. Other alternative injection routes have been studied, namely injection  via sternotomy, endomyocardial  and intracoronary routes. Nevertheless, all methods aforementioned have been associated with limited cardiac function improvements and limited cell survival once implanted in the fibrous myocardium.


To resume, stem cells and delivery routes aforementioned are suitable for cardiomyoplasty as demonstrated safe with some degree of benefit for the patient. However, cardiac remodelling remains limited due to limited cell residency, impact of mechanical forces onto cell survival and tissue hypoxia. Furthermore, lack of cellular electrochemical coupling can lead to arrhythmias. Another point of consideration concerns the use of embryonic stem cells, whereby indifferentiation yields uncontrolled proliferation and possible consequent formation of teratomas. Also iPSCs have been associated with viral infection and eventual oncogenicity. Cardiac tissue engineering is a new technology based on the use of combinations of cells with regenerative capacity, biological and/or synthetic materials, cell signaling agents to induce the regeneration of an organ or damaged tissue. In an ideal scenario, regenerated tissue would reproduce sophisticated asymmetric helicodoidal architecture of the myocardium with the production of specialized extracellular matrix to stimulate vascularization in the implanted tissue. From a cellular perspective, [ 5 ]  available techniques are monolayer cell construct onto temperature-sensitive polymer, where their detachment is driven by behavior of the mechanical properties of the synthetic support without the need of any enzymatic digestion such as trypsin. Cardiomyocites sheets have also been successfully implanted with an observed contractile function as a result of inter-cellular communication between the host and graft. However, from a practical point of view, such approach lacks of translational character as all studies share the lack of reproducibility, i.e. a construct of similar characteristics of the native tissue does not guarantee the same results. Another approach resides in the use of hydrogels. Natural hydrogels such as Matrigel, [ 6 ]  collagen and fibrin have been used as entrapment matrices, wherein the cells to be injected are embedded. However the associated high pressure of injection is associated with a high mortality rate for the cells thereby negatively impacting the benefit ratio of this approach. Furthermore, from a technical point of view, due to the polydispersity of these natural hydrogels, purification is a requisite but very difficult step. Synthetic hydrogels, such as  polyethylene glycol , polylactic acid, polylactic acid-co-glycolic acid, polycaprolactone, polyacrylamide and polyurethane have been proposed.  Metalloproteinase-sensitive polyethylene is of particular interest. Indeed, this polymer modulates its mechanical and biophysical properties accordingly to enzymatic activities associated with cardiomyogenic differentiation of implanted cells. To date, no hydrogel matrix is FDA-approved for stem cell therapy use despite a large number of biomaterials currently commercially available.


A general comment on hydrogel based technologies:


Natural hydrogel are well tolerated by the host and cells due to their mimicking the natural ECM in terms of backbone and microstructure. However they suffer from batch to batch variation (a drawback for current Good Manufacturing Practices (cGMPs) required for clinical application), high degradation rates, and poor tenability. Synthetic hydrogels are reproducible, tunable and amenable regulatory and manufacturing protocols. [ 7 ] [ 8 ] [ 9 ]  Their chemical modification permits the integration of cellular attachment sites and a certain control over degradation rates. Semi-synthetic hydrogels share characteristics of both classes. Indeed, they permit either the modification of the purified natural biopolymers or by coupling the synthetic component with integrin and/or growth factor binding sites.


Cardioplegia  is a solution given to the heart during cardiac surgery, to minimize the damage caused by  myocardial ischemia  while the heart is paused.