Effects of interventricular shunt on indices of left ventricular function.

The accuracies of indices of left ventricle function were examined in an open-chest model in dogs with and without a ventricular septal defect, in which the ventricular shunt was opened and reclosed by a specially designed flowmeter probe with a cap. The systolic time interval, the maximal rate of pressure development in the left ventricle (+LV dP/dt), +LV dP/dt corrected for the isometric pressure (+LV dP/dt/Pd), and the time to +LV dP/dt (t-dP/dt) were determined by recording the aortic flow, ventricular shunt flow, aortic pressure, pulmonary arterial pressure, and left ventricular pressure. The isometric contraction time, the preejectional period, and the ejection time shortened with decrease of the mean aortic pressure and aortic flow, and the mean pulmonary arterial pressure increased after opening the ventricular shunt. When the pulse was varied by atrial pacing, the systolic time interval was affected in dogs both with and without a ventricular septal defect, but "isometric contraction time" was not affected in animals with a ventricular septal defect. Dopamine and methoxamine were used to evaluate the effects of the inotropic state and afterload on these indices. The extents of the changes in the systolic time interval and +LV dP/dt were different in animals with and without a ventricular septal defect, but the changes in preejectional period/ejection time, +LV dP/dt/Pd and t-dP/dt were similar in the two conditions. These results suggest that the systolic time interval and the indices of left ventricular pressure are useful in assessment of cardiac function only in certain conditions.