Radionuclide evaluation of aortic regurgitation.
The timing for valve replacement in patients with aortic regurgitation remains a complex clinical problem. Rest radionuclide angiography measurement of ejection fraction is a simple informative study to help evaluate the appropriate timing for valve replacement in the asymptomatic patients or those with mild symptoms. In patients with normal ejection fractions the disease probably has not yet evolved to the phase in which valve replacement is essential. If the ejection fraction is mildly depressed (0.40 to 0.49) the time is right for intervention. By the time the ejection fraction falls to less than 0.40 the left ventricle is likely damaged and unlikely to regain normal function. If the patient has severe symptoms with maximal medical therapy, surgery is indicated no matter what the ejection fraction. The latter situation can arise especially when aortic regurgitation evolves over a short period, as might be the case in patients with bacterial endocarditis. A single ejection fraction measurement is not as reliable as serial studies. If, for example, the ejection fraction (under similar circumstances) falls from the greater than or equal to 0.50 range to the 0.40 to 0.49 range, the physician should be altered to the possibility that the left ventricle is deteriorating, and surgery should be considered. It should be understood that multiple hemodynamic factors in aortic regurgitation can alter the ejection fraction and could limit its use as the sole measure of left ventricular performance. Other systolic or diastolic parameters cannot be relied on in isolation as an indication or contraindication for aortic valve replacement. The exercise ejection fraction response reflects the total stroke volume and does not distinguish between regurgitant flow and forward flow. It is therefore possible to observe a decrease in ejection fraction in association with an increase in forward stroke volume during exercise as a result of an increase in heart rate and a decrease in peripheral resistance. Accordingly, it is not appropriate to compare the ejection fraction during exercise in aortic insufficiency with the expected response of the normal ventricle. Exercise position (sitting vs. supine) affects loading conditions and ejection fraction response. Because of the complexity of the exercise ejection fraction response, it is not clear that there is a role for exercise ejection fraction measurements in determining the appropriate time for aortic valve replacement. Criteria based on supine exercise may not be applicable to studies in the upright position.(ABSTRACT TRUNCATED AT 400 WORDS)
Miller
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Nuclear Cardiac Imaging Research, University of Texas Health Science Center, San Antonio.
D001021:Aortic Valve / Q000503:physiopathology; D001022:Aortic Valve Insufficiency / Q000000981:diagnostic imaging* / Q000503:physiopathology; D001810:Blood Volume / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D011875:Radionuclide Angiography / Q000379:methods*