Quantitative Evaluation of Indicators of Cardiac Function in an Experimental Animal Model of Chronic Aortic Regurgitation
Huskey, Kathryn D.
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One of the most difficult problems facing cardiologists today involves the therapy of chronic aortic regurgitation, including the timing of aortic valve replacement. Aortic regurgitation refers to a valvular heart disease in which a portion of the blood ejected into the aorta during systole leaks back into the left ventricle during diastole, due to a faulty aortic valve. Evaluation of aortic regurgitation currently focuses on indicators, such as regurgitant fraction, which measure the severity of the regurgitation. This study was designed to explore quantitatively the reliability of regurgitant fraction, and other hemodynamic indicators, as quantitative indices of cardiac work. Using a sheep model of chronic aortic regurgitation, several indicators were measured. Regurgitant flow rates were recorded using electromagnetic flow meters, cardiovascular pressures were obtained from high-fidelity catheters placed in the right femoral artery and left ventricle, and continuous wave Doppler was used to determine mean regurgitant jet velocity. These measurements allowed us to calculate left ventricular stroke work and potential and kinetic energy expenditures due to regurgitation. A strong correlation existed between left ventricular stroke work and both kinetic and potential energy (r2= 0.85, P = 0.001; r2 = 0.78, P <0.0001), pulse pressure (r2= 0.82, p < 0.0001), left ventricular stroke volume (r2= 0.77, P <0.0001) and regurgitant volume (~= 0.76, P <0.0001). The weakest correlation was found between left ventricular stroke work and regurgitant fraction (r2 = 0.39, p = 0.002). Therefore, conventional evaluation of aortic regurgitant severity does not include examination of the most important determinants of left ventricular stroke work. Assessment of cardiac work in patients with chronic aortic regurgitation would be improved by examining factors such as regurgitant, volume and energy expenditure due to the regurgitation.