Aortic stenosis is an abnormal narrowing or stiffening of the aortic valve, which controls the ﬂow of blood from the left ventricle to the aorta (the main artery of the body). As the valve narrows, the left ventricle has to beat harder to push the blood through the aorta and out into the body. The most common cause of aortic stenosis is the gradual buildup of calcium deposits on the valve, a natural conse- quence of aging. Although this condition may appear at about age 60, it usually does not produce symptoms until age 70 or 80. Aortic stenosis also may result from childhood rheumatic fever. When rheumatic fever is the cause, aortic steno- sis usually is accompanied by mitral valve stenosis (see page 227), mitral valve regurgitation (see page 226), or both.
In aortic stenosis, as the ventricle attempts to pump enough blood through the narrowed aortic valve, the left ventricle wall thickens, and the enlarged heart muscle requires an increasing blood supply from the coronary arteries. Eventu-ally the blood supply to the heart becomes insufﬁcient, causing angina (chest pain) on exertion. An insufﬁcient blood supply can damage the heart muscle, reducing its abil- ity to pump blood through the body. This reduced functioning can lead to congestive heart failure (see page 233). A person with severe aortic stenosis may faint on exertion because the narrow valve prevents the ven- tricle from pumping enough blood out of the heart to the rest of the body.
In diagnosing aortic stenosis, a physician will listen for the characteristic heart mur- mur through a stethoscope, note abnormali- ties in the pulse and electrical activity of the heart, and look for an enlarged heart as revealed by a chest X ray. Electrocardio- graphy (ECG; an examination of the elect- rical activity of the heart), echocardiography (an ultrasound examination of the heart), and cardiac catheterization (a diagnostic test in which a thin, ﬂexible tube is inserted into the heart through a blood vessel, to examine the heart) may be used to deter- mine the severity of the stenosis.
In adults with fainting, angina, and short- ness of breath on exertion caused by aortic stenosis, the aortic valve is surgically replaced, preferably before the left ventricle is damaged beyond repair.
Heart Valve Replacement
In cases of a diseased or damaged valve, surgery may be required. Although it is sometimes possi- ble to repair the valve, usually it is necessary to replace it. A replacement valve that is no longer working properly also must be replaced with a new valve.
Replacement valves can be made from human or animal tissue (biologic replacement valves) or from metal and plastic (mechanical replacement valves). Although mechanical valves last longer (20 years or more) than biological valves, they also can pro- mote blood clot formation. This means that a per- son with a mechanical heart valve needs to take long-term therapy with blood-thinning medication to prevent blood clots from forming.
In valve replacement surgery, the person is given general anesthesia. The surgeon opens the chest cavity and exposes the heart (open heart surgery). The heart is temporarily stopped, and a heart-lung machine is used to pump blood throughout the body. The diseased or damaged valve is removed, and the replacement valve is put in position and attached with stitches. The surgeon then restarts the heart and disconnects the heart-lung machine. The chest cavity is closed and stitched together.
To prevent a heart valve infection, a person with a replacement valve must take antibiotics before all dental and surgical procedures.