Treatment for Aortic Stenosis
Valve replacement surgery is the only treatment for aortic stenosis. Because patients with aortic stenosis often also have blockages in the coronary arteries, or coronary artery disease (CAD), surgeons typically treat significant blockages by performing bypass surgery at the same time. For this reason, most patients undergo cardiac catheterization before valve replacement surgery to detect blockages in the coronary arteries.
Patients with aortic stenosis who have no symptoms (i.e., are asymptomatic) and have normal left ventricular function and size do not require immediate valve replacement surgery. Treatment for these patients usually involves careful medical follow-up, including check-ups to be sure that symptoms have not developed, and echocardiograms every 3 months to 1 year to assess the function and size of the left ventricle. If a symptom develops, the patient should inform the physician immediately and should not wait until the next scheduled checkup.
Valve replacement surgery is usually indicated in patients who have been diagnosed with severe AS, regardless of symptoms, and especially if dyspnea, angina, or syncope is present. Strenuous physical exertion should be avoided in those with severe AS.
If echocardiogram or cardiac catheterization suggests that the left ventricle is beginning to decompensate due to the strain of pumping blood through a stenotic aortic valve, valve replacement surgery is indicated. The two main signs of decompensation are (1) dilation of the left ventricle and (2) loss of vigorous contraction of the left ventricle (falling ejection fraction).
Normally, the left ventricle ejects approximately 60% of the blood contained within the left ventricle with each "beat" (contraction). This percentage of blood that is ejected into the aorta with each beat is called the ejection fraction. As the heart loses the ability to contract vigorously, the ejection fraction falls.
Patients with ejection fractions of approximately 40% to 45% have mildly depressed ejection fractions; those with ejection fractions of approximately 30% to 40% have moderately depressed ejection fractions; and those with ejection fractions of 10% to 25% have severely depressed ejection fractions. Even a slight drop in the ejection fraction can be an indication to proceed with valve replacement surgery. The more the ejection fraction falls, the greater the indicator for valve replacement surgery.
Valve Replacement Surgery
Replacement of the aortic valve requires open-heart surgery, in which the breast bone (sternum) is split down the middle, allowing access to the heart. The heart is stopped during critical parts of the operation and a special machine pumps oxygenated blood throughout the body. The diseased valve is removed and a new valve is sewn in.
There are three basic types of valves used to replace the diseased heart valve. A porcine valve is made of tissue from a pig (Figure 1).
The advantage of a porcine valve is that it poses no significant risk for blood clots on the valve; thus, patients do not require blood thinner medication. The disadvantage is that after approximately 10 years, these valves may degenerate and must be replaced.
A mechanical valve is fashioned from metal and synthetic materials. The most commonly used mechanical valve, St. Jude's valve (Figure 2), consists of two semicircular discs that open with each contraction of the left ventricle and close when the ventricle relaxes.
The advantage of a mechanical valve is that it is quite durable, often lasting more than 20 years. The disadvantage is that there is a small risk for a blood clot to form on the valve. This blood clot can break off, travel to the brain, and cause stroke. To prevent this complication, patients who receive mechanical heart valves are treated with warfarin (Coumadin®), a blood thinner that decreases the risk for blood clot formation.
A homograft valve is an aortic valve that has been taken from a human organ donor. These valves are not associated with a significant risk for blood clot formation and, thus, do not require blood thinner therapy. No long-term follow-up data are yet available regarding the durability of these valves.
There have been significant advances in the way valve replacement surgery is performed, and the risk for complications is low (approximately 3% to 5% in otherwise healthy patients).
Complications include bleeding, infection, kidney failure, stroke, heart attack, and death.