EFFECTS OF PRELOAD, AFTERLOAD AND INOTROPY ON DYNAMICS OF ISCHEMIC SEGMENTAL WALL-MOTION

Objectives. This study sought to explore the separate and combined eff ects of changes in preload, afterload and contractility on the dynamic s of systolic bulging, Background. The extent of ischemic systolic bul ging has been shown to be mechanically disadvantageous to left ventric ular pump performance, The factors that determine ischemic segmental w all motion have not been systematically studied, Methods. Fourteen bea gles were instrumented with sonomicrometers, micromanometer pressure g auges and a balloon in the inferior vena cava, Regional function was e valuated before and after 90 s of proximal left circumflex coronary ar tery occlusion, Occlusions were repeated after increasing systolic pre ssure by 5 to 10 (afterload I) and 15 to 20 mm Hg (afterload II) with graded aortic occlusion during inotropic stimulation with dobutamine ( 2.5 and 5 mu g/kg body weight per min intravenously), with simultaneou s 5-mu g/kg per min dobutamine infusion and afterload II and during 2. 5% halothane (negative inotrope) concentration, A 20-min recovery peri od was allowed between each stage of the experiment so that regional f unction returned to its preocclusion level, Ischemic wall motion was c haracterized by percent systolic bulging and its peak positive systoli c lengthening rate (+dL/dt). Results. Because bulging is markedly infl uenced by regional preload, systolic bulging was characterized over a Ride range of end-diastolic lengths of the ischemic segment during cav al balloon occlusion, During each intervention, a decrease in regional preload increased the extent of percent systolic bulging, This preloa d dependency was more pronounced with dobutamine infusions. An increas e in afterload was not associated with increased percent systolic bulg ing at any given preload. At a predetermined preload, bulging was not appreciably altered when an increase in left ventricular systolic pres sure was not associated with a change in peak positive first derivativ e of left ventricular pressure (+dP/dt) but,vas significantly worse wh en peak +dP/dt increased. Dobutamine caused a dose-dependent increase in percent systolic bulging and peak +dL/dt that was positively correl ated with peak +dP/dt. Conclusions. By using different loading and ino tropic interventions and analyzing the regional wall motion behavior o ver a range of regional preloads, we can conclude that preload and rat e of pressure (tension) development are the principal determinants of systolic bulging, Increases in left ventricular pressure alone had a m inimal effect on systolic bulging. (C) 1997 by the American College of Cardiology.