Timing of aortic-valve replacement

Clinical outcomes in adults with aortic stenosis are determined primarily by clinical symptoms, the severity of valve obstruction, and the left ventricular response to pressure overload. Assessment of patients and management decisions should take all three of these factors into account.

The presence or absence of symptoms is the key element in decision making (FIGURE 4 Diagnostic Approach to the Treatment of Suspected Aortic Stenosis.).

There is robust evidence that aortic-valve replacement prolongs life in patients with symptomatic severe aortic stenosis, regardless of the type or severity of symptoms or the response to medical therapy. However, accurate measures of the severity of stenosis are needed to ensure that valve obstruction — rather than concurrent coronary, pulmonary, or systemic disease or other conditions — is the cause of symptoms. In a patient with typical symptoms, a maximum transvalvular velocity of 4 m per second or greater, in conjunction with calcified immobile valve leaflets, confirms the diagnosis of severe aortic stenosis. With symptomatic, severe, high-gradient aortic stenosis, calculation of the valve area or indexed valve area does not improve the identification of patients who will benefit from valve replacement (FIGURE

5 Indications for Aortic-Valve Replacement (AVR).).

In contrast, in asymptomatic patients with aortic stenosis and normal left ventricular systolic function, the usefulness of measures of severity is in identifying patients who will soon become symptomatic, thus indicating the need for frequent follow-up and consideration of elective intervention. Intervention is not needed until symptoms supervene, because the risk of sudden death is less than the risk of intervention, even when valve obstruction is severe. With very severe aortic stenosis, the rate of symptom onset is so high that elective valve replacement may be reasonable in selected cases.

Given the importance of symptom onset in clinical decision making, primary care physicians and cardiologists need to be alert to the presence of a systolic murmur in older adults with exertional dyspnea, chest pain, or dizziness. In the case of apparently asymptomatic patients with severe aortic stenosis, detailed questions should be asked about levels of physical activity, because many patients unconsciously limit activities to avoid symptoms as valve obstruction slowly worsens. When the clinical history is unclear, standard treadmill exercise testing is helpful to detect provoked symptoms, ensure that blood pressure rises appropriately, and measure exercise capacity objectively.

Evaluation of the severity of stenosis is more difficult when the valve appears to be calcified with only a moderately elevated transvalvular velocity (3 to 4 m per second) or mean transaortic pressure gradient (20 to 40 mm Hg), but the calculated valve area is less than 1.0 cm². This situation, termed low-flow, low-gradient aortic stenosis, occurs most often in patients with a reduced left ventricular ejection fraction (< 50%). These patients may have severe aortic stenosis with afterload mismatch causing left ventricular dysfunction, in which case valve replacement will prolong survival and improve the ejection fraction. Alternatively, valve obstruction may only be moderate, with the apparently small valve area caused by primary dysfunction of the myocardium. Low-dose dobutamine stress echocardiography is a useful additional test in such patients. During stress testing, a transvalvular velocity that increases to 4 m per second or higher with the valve area remaining less than 1.0 cm² is consistent with severe aortic stenosis. Conversely, a transvalvular velocity of less than 4 m per second or an increase in valve area is consistent with only moderate valve obstruction, and evaluation for other causes of left ventricular dysfunction and medical therapy for heart failure are appropriate.

Diagnosis of low-flow, low-gradient, severe aortic stenosis with a normal left ventricular ejection fraction is particularly challenging. Because transvalvular velocity is less than 4 m per second, diagnosing this condition depends on indexing the valve area and volume flow rate to the body-surface area. In symptomatic patients with a calcified aortic valve and decreased leaflet mobility, an indexed valve area of 0.6 cm² per square meter of body-surface area and a stroke volume index of less than 35 ml per square meter are consistent with a diagnosis of severe aortic stenosis. This situation is seen most often in elderly women with left ventricular hypertrophy, small ventricular volumes, diastolic dysfunction, and reduced longitudinal shortening.