The influence of preload and heart rate on Doppler echocardiographic indexes of left ventricular performance: comparison with invasive indexes in an experimental preparation.

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Abstract
We evaluated the ability of Doppler echocardiography to assess left ventricular performance in six open-chest dogs studied under various conditions. Intravenous infusion of nitroglycerin were used to vary preload, atrial pacing was used to control heart rate, and changes in inotropic state were induced by two different doses of dobutamine (5 and 10 .mu.g/kg/min iv) and by administration of propranolol (1 mg/kg iv). Left ventriclar anterior wall myocardial segment length was used as an index of preload. Maximum aortic blood flow, peak acceleration of aortic blood flow, and dP/dt were measured with an electromagnetic flow probe around the ascending aorta and a high-fidelity pressure transducer in the left ventricle. A continuous-wave Doppler transducer applied to the aortic arch was used to measure peak aortic blood velocity, mean acceleration, time to peak velocity, and the systolic velocity integral. The differences between mean values obtained under different inotropic conditions were significant at the p < .01 level for peak velocity and at the p < .05 level for mean acceleration. Within a given animal, Doppler measurements of peak velocity correlated very closely with maximum aortic flow (r = .96), maximum acceleration of aortic flow (r = .95), and with maximum dP/dt (r = .92). Mean acceleration measured by Doppler echocardiograhy also correlated very closely with conventional indexes, but was subject to greater interobserver variability. Doppler measurements of time to peak and the systolic velocity integral correlated less well with conventional hemodynamic indexes. In conclusion, Doppler measurements of peak aortic blood velocity and mean acceleration offer an effective means to noninvasively assess short-term changes in left ventricular performance under conditions of varying preload, heart rate, and inotropic state.