Myocardial contractility evaluated from cross-oriented segments during β-adrenergic blockade or sympathetic nerve stimulation

Abstract

In patient and experimental models of regions of the left ventricle subjected to ischaemia and thus made dysfunctional it is important to characterize the inotropic state of the remaining myocardium. Eighteen pentobarbitone-anaesthetized open-chest cats with an acute circumflex coronary artery occlusion were therefore studied during either sympathetic nerve stimulation (n = 9), or after beta-adrenergic blockade (n = 9). Myocardial contractility was evaluated from cross-oriented segments in the left ventricular anterior wall during stable haemodynamics and during 5 s inferior caval occlusion. The end-systolic pressure-length relationship of longitudinal segments was rather insensitive to beta-adrenergic blockade and sympathetic nerve stimulation. The end-systolic pressure-length relationship of circumferential segments was suitable as a marker of contractility in the low contractility range, whereas the peak systolic shortening velocity parameter was more suitable in the upper contractility range. The pressure-length loop area versus end-diastolic length relationship of both circumferential and longitudinal segments reflected both increased and decreased left ventricular inotropic state. We therefore conclude that the pressure-length loop area versus end-diastolic length relationship is the best index of regional myocardial contractility in regional ischaemic hearts.