Aortic valve replacement, AVR
Aortic valve replacement is a type of open heart surgery where damaged aortic valve is replaced with an artificial valve to restore its normal function.
Structure of the aortic valve
Heart consists of cavities: two upper and two lower chambers. The upper chambers are called atria and the lower larger chambers are called ventricles. There are two valves in every ventricle.
- A valve that controls the blood flow out of the ventricle (the pulmonary valve on the right or aortic valve on the left)
- A valve that controls blood flow into the ventricle (the tricuspid on the right or mitral valve on the left)
Left ventricle pumps the blood from the heart through the aorta (the largest artery in the body) to the rest of the body and the one-directional flow is controlled by aortic valve. Aortic valve normally opens during cardiac contraction (systole) to allow the blood flow without any resistance and closes during cardiac relaxation (diastole) to prevent the blood from leaking back to the heart.
Indications for aortic valve replacement
- 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 through it into the left ventricle
Diseased aortic valve is commonly both stenotic and regurgitating. Aortic stenosis, aortic regurgitation and other types of valve disease are diagnosed with echocardiography (transthoracic, TTE or transoesophageal, TOE). Surgery is option of choice to replace the aortic valve when aortic valve fails to work properly.
Treatment of aortic valve disease
Medication has only a supportive role in treatment of valve disease (eg ACE inhibitors and diuretics in aortic regurgitation). The frst line treatment of significant aortic stenosis and regurgitation is aortic valve replacement (open heart surgery where diseased valve is removed and replaced by an artificial metallic or tissue valve).
A recent alternative option for some patients is TAVI (transcatheter aortic valve implantation) where the new valve is delivered via catheter placed usually in the artery at the top of the leg. As a bridge to definitive treatment, aortic balloon valvuloplasty where the aortic valve is stretched by a special balloon, can be used. Alternative procedures are considered only for patients who are frail or with comorbidities which would make conventional AVR too risky or impossible.
Technique of aortic valve replacement
The heart is accessed by cutting the breastbone and opening chest. A cardiac perfusion machine (heart-lung bypass) is used to drive the circulation and heart is stopped. The surgeon then removes the diseased aortic valve and sutures prosthesis (metallic or tissue artificial valve) in place. Heart-lung machine is disconnected and the heart starts beating again. The chest wound is closed by wires and skin sutured with stitches.
Aortic valve replacement is a substantial procedure and carries certain risk. About 2% patients undergoing the operation don’t survive the procedure and additionally, there is some risk of perioperative heart attack, stroke, kidney failure and other complications. Postoperatively, metallic aortic valve requires anticoagulation with warfarin and presence of artificial valves increases risk of infective endocarditis. However, all these risks are manageable and need to be considered in the context of very poor prognosis of patients with untreated severe aortic stenosis or aortic regurgitation.