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), percutaneous or transcatheter aortic valve replacement (TAVR; also PAVR, PAVI, TAVI), and robotic aortic valve replacement (RAVR).
A cardiologist can evaluate whether a heart valve repair or valve replacement would be of benefit.
History
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. The first combined robotic aortic valve replacement (RAVR) and coronary artery bypass grafting (CABG) was performed on October 31, 2024. Cardiothoracic surgeon Vinay Badhwar of West Virginia University Heart and Vascular Institute succeeded through a single small incision, using a da Vinci Xi robot.
Anatomy, physiology and pathophysiology +Classification of aortic stenosis severity U/S findings Mild Moderate Severe Aortic valve area, cm2 >1.5 1.0-1.5 <1.0 Aortic valve area index, cm2/m2 - - 0.6 Mean pressure gradient, mmHg 25 25-40 >40 Peak jet velocity, m/s <3 3-4 >4
+Classification of aortic regurgitation severity U/S findings Mild Moderate Severe Jet width of left ventricular outflow tract <25% 25–65% >65% Vena contracta width, cm <0.3 0.3–0.6 0.6 Regurgitant volume, mL per beat <30 30–49 60 Regurgitant fraction, % 30 30–49 >50 Regurgitant orifice area, cm2 <0.10 0.10–0.30 >0.30
The aortic valve is one of the two semilunar valves of the heart with three cusps, or leaflets. 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). 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.
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.
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.
Indications for surgery
Guidelines for aortic valve replacement 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, and the European Society of Cardiology and the European Association for Cardio‑Thoracic Surgery Guidelines for the management of valvular heart disease.
Aortic stenosis
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. 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.
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.
Aortic insufficiency Many people with aortic insufficiency often do not develop symptoms until they have had the condition for many years. 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.
Types of valves
There are two basic types of replacement heart valve: tissue (bioprosthetic) valves and mechanical valves.
Tissue valves
Tissue heart valves are usually made from animal tissue (heterografts) mounted on a metal or polymer support. Bovine (cow) tissue is most commonly used, but some are made from porcine (pig) tissue. The tissue is treated to prevent rejection and calcification (where calcium builds up on the replacement valve and stops it working properly).
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. 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.
Tissue valves can last 10–20 years. However, they tend to deteriorate more quickly in younger patients. 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.
Stented and stentless tissue valves are available. Stented valves come in sizes from 19 mm to 29 mm. 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) and can be helpful when dealing with small aortic root. However, stentless valves take more time than stented valves to implant.
Mechanical valves Mechanical valves are made from synthetic materials, such as titanium or pyrolytic carbon. Their durability is long life, while tissue valves can last for up to 15–20 years. 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). The sound of the valve can be heard very rarely, often as clicks, and might be disturbing. 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.
Valve selection
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.
Surgical replacement
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.