Factors delaying end ejection from end systole of ventricle.

Although the end of ejection of the left ventricle has been generally accepted as almost synonymous with the end of mechanical systole of the ventricle, recent experimental studies showed the cases in which end ejection lagged markedly behind end systole as identified by the time at which the ventricular pressure-volume data point reached the peak isovolumic pressure-volume relation curve. To obtain a better insight into cardiovascular conditions of the delayed end ejection, a computer simulation study was carried out in which the performance of a time-varying elastance model of the ventricle connected with a modified Windkessel model of the arterial load was analyzed. Any change in the Windkessel parameters, ventricular contractility and heart rate sensitively shifted end ejection relative to end systole. Although end ejection coincided with end systole under limited circumstances, end ejection variably lagged behind end systole undermost circumstances. These results suggest that the interval between end systole and end ejection of the left ventricle in vivo is also variable depending on changes in the arterial loading conditions, ventricular contractility and heart rate.