The Effect of Changes in Afterload on Doppler Echocardiographic Indexes of Left Ventricular Performance

To investigate the influence of changes in afterload on Doppler echocardiographic determination of peak aortic blood velocity, mean acceleration, and systolic velocity integral, eight dogs with their chests opened were studied in four inotropic states at varying levels of heart rate and mean aortic blood pressure. Data were collected in the control state, at two different levels of dobutamine administration (5 and 10 μg/kg/min intravenously), and after administration of propranolol (0.5 mg/kg intravenously). In each inotropic state, phenylephrine was infused intravenously to produce at least two successive steady state increases of 10 mm Hg or more in mean aortic blood pressure. Within a given animal, peak velocity emerged as the Dopler index most closely correlated with changes in QmaxdQ/dt, and dP/dt (r = 0.94, 0.91, and 0.89, respectively). Mean acceleration also correlated closely with the invasive indexes (r = 0.87, 0.89, and 0.89). The effect of changes in mean aortic blood pressure on Doppler index measurements was not statistically significant in any of the inotropic states and did not affect the closeness of their correlation with the invasive indexes. We conclude that Doppler echocardiographic measurements of aortic blood peak velocity and mean acceleration remained as sensitive to changes in the inotropic state under conditions of varying increases in afterload as did the conventional invasive indexes tested.