Aortic valve replacement (AVR) and transcatheter aortic valve implantation (TAVI) are invasive procedures where damaged aortic valve is replaced with a new valve to restore its normal function.

Cardiac anatomy

The heart consists of four chambers; atria are the smaller upper chambers, and ventricles are the larger lower chambers. There are two valves in each ventricle:

• A valve that controls blood flow out of the ventricle (the pulmonary valve on the right and the aortic valve on the left).
• A valve that controls blood flow into the ventricle (the tricuspid valve on the right and the mitral valve on the left).

The left ventricle pumps the blood from the heart through the aortic valve into the aorta (the largest artery in the body) and the rest of the body. The aortic valve normally opens during cardiac contraction (systole) to allow the blood flow without any resistance. It closes during cardiac relaxation (diastole) to prevent the blood from leaking back to the heart.

Indications for aVR

• Aortic stenosis (narrowing of the valve) - aortic valve becomes calcified, stiff and rigid, obstructing normal blood flow.
• Aortic regurgitation (leaking of the valve) – the aortic valve leaks, and blood flows back into the left ventricle.

The diseased aortic valve is commonly both stenotic and regurgitating. Both aortic stenosis and aortic regurgitation are diagnosed with echocardiography (transthoracic or transoesophageal echo). Significant aortic valve disease leads to tiredness, breathlessness, chest discomfort, dizziness and blackouts. The heart has to work harder in stenosis to overcome the resistance of the diseased stenotic valve and to pump again the blood, which returned to the left ventricle from the aorta in regurgitation. Both aortic stenosis and aortic regurgitation can ultimately lead to heart failure.

Treatment of aortic valve disease

Medication has only a supportive role in treating aortic valve disease (e.g. ACE inhibitors and diuretics in aortic regurgitation). The curative treatment of significant aortic stenosis or regurgitation is valve replacement. There are two options for aortic valve replacement:

• Surgical aortic valve implantation, SAVR (open heart surgery where the diseased valve is removed and replaced by an artificial metallic or tissue valve).
• Transcatheter aortic valve implantation, TAVI (a procedure where the new valve is delivered via a catheter usually placed in the artery at the top of the leg).
  
  Sometimes, aortic balloon valvuloplasty, where a special balloon stretches the aortic valve, is used as a bridge to definitive treatment or as a palliative treatment in patients who are not suitable for valve replacement because of serious comorbidities or frailty.

Technique of SAVR

The heart is accessed by cutting the sternum (breastbone) and opening the chest. A cardiac perfusion machine (heart-lung bypass) is used to drive the circulation, and the heart is stopped. The surgeon then removes the diseased aortic valve and sutures the prosthesis (metallic or tissue artificial valve) in place. The heart-lung machine is disconnected, and the heart starts beating again. The chest wound is closed with wires and skin sutured with stitches.

Risks

Aortic valve replacement is a substantial procedure and carries a risk of mortality and morbidity, including perioperative heart attack, stroke, kidney failure and other complications. Postoperatively, the metallic aortic valve requires anticoagulation with warfarin (NOACs, new oral anticoagulant drugs, such as apixaban, edoxaban, rivaroxaban, or dabigatran can't be used in this indication), and the presence of artificial valves increases the risk of infective endocarditis. However, all these risks are manageable and need to be considered in the context of the very poor prognosis of patients with untreated severe aortic stenosis or aortic regurgitation.