Evaluation of the pre-ejection period as an estimate of myocardial contractility in dogs

Abstract

The pre-ejection period, measured externally by subtracting the left ventricular ejection time from the total systolic time, was evaluated in dogs under a variety of experimental conditions in order to determine the effect of various levels of inotropic stimuli, changes of heart rate, aortic diastolic pressure and left ventricular end-diastolic pressure. In addition, the pre-ejection period was systematically compared to 2 more completely evaluated internal indexes of myocardial contractility: the time to maximal dp/dt (first derivative of left ventricular pressure) and the maximal dp/dt divided by instantaneous left ventricular pressure. No effect of heart rate on the pre-ejection period was noted when left ventricular end-diastolic pressure, aortic diastolic pressure and contractile indexes were held constant. Increases in aortic diastolic pressure caused significant but small increases in the pre-ejection period during constancy of end-diastolic pressure, heart rate and contractile indexes. Increases in left ventricular end-diastolic pressure were found to alter markedly the pre-ejection period in an inverse fashion at fixed levels of aortic diastolic pressure, heart rate and contractile indexes. There was, however, a significant correlation between the pre-ejection period and the internal indexes of contractility over a wide range of inotropic stimuli in experiments in which left ventricular end-diastolic pressure was shown to vary in a random manner. These studies indicate that the pre-ejection period may be used as an index of myocardial contractile state in situations in which the left ventricular end-diastolic pressure is constant or proved not to vary systematically under the conditions being studied. During all studies, internal and external measurements of the preejection period were found to correlate well at levels of left ventricular end-diastolic pressure below 12 mm Hg, but they were increasingly divergent at higher levels of end-diastolic pressure.