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The aortic valve has three cusps. When the aortic valve is open, the normal size of the orifice is 3-4 cm².
Function & 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).
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.
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 either become leaky (regurgitant or insufficient) or stuck partially shut (stenotic). Aortic valve replacement currently requires open heart surgery. Research is being done now on to develop valves that can be implanted using a catheter without open heart surgery.
There are two basic types of valves that can be used for aortic valve replacement, mechanical and tissue valves. Modern mechanical valves can last indefinitely (the equivalent of over 50,000 years in an accelerated wear valve tester). However, current mechanical heart valves all require lifelong treatment with a blood thinner, warfarin, which requires monthly blood tests to monitor. This process of thinning the blood is called anticoagulation. Tissue heart valves, in contrast, do not require anticoagulation but have a limited lifespan. Traditional tissue valves, made of pig heart valves, will last on average 15 years before they require replacement.
The most popular mechanical aortic valve has been the St. Jude valve. The St. Jude valve is a bileaflet valve consisting of two small half circle shaped disks. The disks are housed in a cylindrical housing and held in place by two small outpouchings. The disks and the housing are coated with pyrolytic carbon , an extremely hard material. Other mechanical valves include the bileaflet ATS valve, the bileaflet Carbomedics valve and Sorin valves. The single leaflet Bjork-Shiley valve and the single leaflet Medtronic-Hall valve.
Tissue valves can be made of porcine (pig), bovine (cow), or human tissue. The earliest commercial tissue valves were made of pig tissue. More recently, the most popular tissue valve has been made of bovine (cow) heart pericardial tissue.
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 harvested after the patient expires. The durability of homograft valves is probably the same for porcine tissue valves. Another procedure for aortic valve replacement is the Ross procedure 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) is then used to replace the patients own pulmonary valve.
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