Many problems can interfere with the proper functioning of a valve. They may be congenital (abnormal from birth), infectious (endocarditis), inflammatory (rheumatic fever), or just wear and tear over the years. In general, heart valve problems take one of two forms:
The most common aortic valve problem in young people is to be born with only two leaflets (bicuspid) instead of three (tricuspid), usually resulting in stenosis. This abnormal structure causes turbulence in the blood flow that creates stress points on the valve. Statistically, bicuspid valves are three times more common in men than in women. Symptoms may occur at birth or appear after many years. It is estimated that at least 1% of the population in America is born with a bicuspid aortic valve.
The body responds to the repeated trauma of opening and closing this abnormal valve by trying to strengthen the tissue. This “strengthening” often produces scarring and ultimately calcification, both on and around the valve, which restricts blood flow. If the valve scars partially shut, the heart must produce more pressure to get the same amount of blood across the valve. Thus, the heart must work harder.
Fortunately, the body is engineered with considerable reserve. Most people do not notice symptoms until the opening is less than half the normal size. Symptoms commonly associated with this disorder are shortness of breath during strenuous activity, chest pain, dizziness, or fainting. Greater demands placed on the heart by strenuous activity cause these symptoms, because the heart is already using its reserve capacity.
The severity of stenosis is expressed by pressure gradient and valve area determined by echocardiogram. The velocity of the red blood cells is determined by the echo Doppler method and formulas have been developed to translate this into pressure and area measurements. The normal aortic valve has a valve area of about 2.5 square centimeters. Most patients do not experience any problems until this falls to less than 1.0. By the time it reaches 0.6 most have symptoms of shortness of breath or chest pain on exertion. Fainting can also occur. A valve of 0.3 is considered too small to survive.
In general, guidelines for surgery in aortic stenosis recommend holding out until symptoms develop. However, stress testing may also be appropriate in patients who have extreme exertional demands to see what happens to the heart under controlled conditions. Sudden death in young athletes happens too often when unsuspected aortic stenosis is pushed to extremes.
(a.k.a. Aortic Insufficiency)
Aortic Regurgitation produces a different kind of strain on the heart. The failure of the aortic valve to close properly allows blood to leak back into the left ventricle, instead of continuing up through the ascending aorta. The heart must compensate for this leakage to keep up with the demand for blood throughout the body.
To compensate for leakage, the heart can beat faster or pump more blood with each beat. The heart typically chooses the latter, because it needs time between beats to relax and nourish itself. To pump more blood with each beat the heart must expand, making the hollow space in the left ventricle larger. An enlarged left ventricle can be filled with more blood than a normal sized left ventricle. As the heart squeezes the enlarged left ventricle, more blood is pumped per beat.
Left Ventricular Dilatation (expansion) is well tolerated to a point (about twice its normal dimensions). However, like an elastic waistband that keeps getting stretched, ultimately, it cannot return to normal. Irreversible damage to the heart occurs if it stretches too far.
Echo cardiograms are used to follow the course of this dilatation and determine the severity of the regurgitation. In general, the left ventricular end systolic dimension should never exceed 5.5 cm and some cardiologists believe 5.0 is to big. The ejection fraction should also be monitored and not allowed to fall below 50%. Exercise echo’s or nuclear ventriculograms can also be used to test the reserve capacity of the heart. An increase in ejection fraction is normal with exercise. Failure to increase or evidence of decrease in ejection fraction with exercise is a sign that surgery should be considered sooner rather than later to prevent further loss of reserve. This is extremely important because many patients have little if any symptoms (usually shortness of breath on exertion) until the heart has been damaged to a great extent. Of course, if symptoms should appear before the numbers look bad, the doctor should listen to the patient! Symptoms are an indication for surgery.
Medications such as nifedipine and possible ACE inhibitors or ARB’s may allow surgery to be delayed in asymptomatic patients for as long as two years, but these patients must be followed closely with echo for signs of deterioration. Every six months is reasonable.