When congestive heart failure occurs in association with aortic regurgitation, it is generally agreed that surgical valve replacement is the treatment of choice. In patients with definite severe aortic regurgitation but who have no symptoms and may be fully functional, one or more parameters of left ventricular (LV) function are measured, usually be echocardiography, and followed serially. An end-systolic diameter of 5.5 cm has been advocated by some as an upper limit beyond which surgery leads to better functional results and survival. Similarly, a decrease in ejection fraction from normal to borderline (e.g.
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45-50%) is also used. The absolute end-diastolic diameter of the LV is a less reliable parameter indicating surgery, though markedly enlarged hearts (e.g. diameters of 8-9 cm by echocardiography) are perhaps less likely to return entirely to normal even if surgery is performed; increasing end-diastolic diameters serve to alert the physician to the need for surgery in the near future.
Is Doppler echocardiography accurate in diagnosing prosthetic aortic stenosis?
When bioprosthetic leaflets thicken and calcify, they may become stenotic. Doppler echocardiography may accurately define the pressure gradient in these cases, just as in stenosis of native valves. However, mechanical prostheses have a variety of orifices, depending on the type of valve. In these cases, the spectral Doppler recording may be in significant error, particularly in overestimating the gradient. St. Jude Medical valves, for example, have a narrow central orifice between the two leaflets. The velocity of blood flow through this slit may be very high, leading to a false diagnosis of prosthetic stenosis. When there is doubt about the severity of prosthetic obstruction, transesophageal echocardiography or cardiac catheterization with hemodynamic recording of pressure is extremely helpful.
When is valve replacement indicated for aortic stenosis?
When congestive heart failure, angina pectoris, and syncope appear. Usually, the aortic valve area associated with such symptoms is about 0.7 cm2 or less. Because aortic stenosis occurs most often in older patients, knowledge of the coronary artery anatomy and its contribution to the angina and congestive heart failure is required. Patients with significant aortic stenosis but without symptoms may be followed closely without surgery. Occasionally, severe LV hypertrophy may be present causing LV diastolic dysfunction with symptoms of pulmonary congestion but with well-maintained systolic function; in these cases, surgery is often warranted.
How may prosthetic mitral valves be evaluated for stenosis?
When a patient with a prosthetic mitral valve begins to develop new or increased symptoms of pulmonary congestion, the possibility of prosthetic stenosis due to thrombus formation, fibrosis with leaflet restriction, or valve dysfunction must be considered. The appearance of the leaflets, both bioprosthetic and mechanical, on the two-dimensional echocardiographic image is of considerable use, especially if the leaflets are well visualized and are seen to move well. Because such visualization is not always achieved, alternative approaches are necessary. Bioprosthetic valves may be evaluated reasonably well with spectral Doppler recordings. The peak inflow velocity and the pressure half-time of the deceleration phase of inflow may be used to compute a mitral valve area. These parameters are not accurate with mechanical prostheses, although abnormal values may be useful clues to dysfunction. In these cases, transesophageal echocardi-ograph, hemodynamic study by cardiac catheterization may be needed.