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|Frontal view of the Aortic valve|
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The aortic valve is one of the four valves of the heart. It normally has three leaflets, although in 2% of the population it is found to congenitally have two leaflets. It lies between the left ventricle and the aorta.
Function and physiology
During ventricular systole, pressure rises in the left ventricle. When the pressure in the left ventricle rises above the pressure in the aorta, the aortic valve opens, allowing blood to exit the left ventricle into the aorta. When ventricular systole ends, pressure in the left ventricle rapidly drops. When the pressure in the left ventricle decreases, the aortic pressure forces the aortic valve to close. The closure of the aortic valve contributes the A2 component of the second heart sound (S2).
Disease of the aortic valve
There are two protypical processes that can affect the aortic valve - aortic stenosis in which the valve fails to open fully, thereby obstructing blood flow out from the heart, and aortic insufficiency, also called aortic regurgitation, in which the aortic valve is incompetent and blood flows passively back to the heart in the wrong direction. These two conditions frequently co-exist.
- Common causes of aortic stenosis include rheumatic fever, degenerative calcification, and congenital diseases such as bicuspid aortic valve.
- Common causes of aortic regurgitation include dilation of the aorta, previous rheumatic fever, infection, i.e. infective endocarditis, degeneration of the aortic valve, and Marfan's syndrome.
Bicuspid aortic valve
The most common congenital abnormality of the heart is the bicuspid aortic valve. In this condition, instead of three cusps, the aortic valve has two cusps. This condition is often undiagnosed until later in life when the person develops symptomatic aortic stenosis. Aortic stenosis occurs in this condition usually in patients in their 40s or 50s, an average of 10 years earlier than can occur in people with congenitally normal aortic valves.
Patients with Turner's Syndrome usually have associated bicuspid aortic valves.
Aortic Valve Replacement
Aortic valve replacement means that a patient's aortic valve is replaced by a different valve. The aortic valve can be affected by a range of diseases and require aortic valve replacement. The valve can become either leaky (regurgitant or insufficient) or stuck partially shut (stenotic). Aortic valve replacement currently requires open heart surgery. Research is being done now to develop valves that can be implanted using a catheter without open heart surgery. There are two basic types of artificial heart valve, mechanical valves and tissue valves. Tissue heart valves are usually made from animal tissues, either animal heart valve tissue or animal pericardial tissue. The tissue is treated to prevent rejection and to prevent calcification.
There are alternatives to animal tissue valves. In some cases, a human aortic valve can be implanted. These are called homografts. Homograft valves are donated by patients and recovered after the patient expires. The durability of homograft valves is probably the same as for porcine tissue valves. Another procedure for aortic valve replacement is the Ross procedure (after Donald Ross) or pulmonary autograft. The Ross procedure involves going to surgery to have the aortic valve removed and replacing it with the patient's own pulmonary valve. A pulmonary homograft (a pulmonary valve taken from a cadaver) or a valvular prothesis is then used to replace the patient's own pulmonary valve.
The first minimally invasive aortic valve surgery took place at the Cleveland Clinic in 1996.
Another option for aortic valve replacement is TAVR or TAVI, Transcatheter Aortic Valve Replacement or Transcatheter Aortic Valve Implantation. This procedure is for select patient criteria and offers a minimally invasive option for patients with severe or symptomatic aortic stenosis. See: http://en.wikipedia.org/wiki/Percutaneous_aortic_valve_replacement