HIGH AFTERLOAD DURING 10 MIN OF REGIONAL ISCHEMIA AFFECTS DIASTOLIC CREEP BUT NOT SYSTOLIC FUNCTION IN REPERFUSED (STUNNED) MYOCARDIUM

The effect of afterload during regional ischaemia on myocardial stunni ng was studied in 15 pentobarbital anaesthetized cats. 10 min occlusio n of the left anterior descending artery (LAD) was followed by 60 min of reperfusion. Afterload was decreased by intravenous infusion of nit roglycerine 3-8 mu g kg(-1) min(-1) in group I (n = 8): left ventricul ar peak systolic pressure (LVSP) 84+/-4 mmHg (mean+/-SEM) during coron ary artery occlusion. In group ii (n = 7) LVSP was increased to 188+/- 10 mmHg by inflating an intraaortic balloon during coronary artery occ lusion. Regional function in the LAD perfused region was evaluated by cross-oriented sonomicrometry. Myocardial tissue blood flow was evalua ted by radio-labelled microspheres. Afterload alterations did not affe ct regional systolic shortening (10.8+/-2.0% vs. 11.0+/-1.5 % in group I and II, respectively, after 60 min of reperfusion). However, increa sed end-diastolic dimensions (diastolic creep) in both the circumferen tial and longitudinal segments were markedly more pronounced in the hi gh afterload group (group II). Also important, the markedly increased myocardial tissue blood flow during reperfusion in group II as compare d with group 1 (2.30+/-0.18 vs. 1.34+/-0.08 mL min(-1) g(-1) and 2.58/-0.23 vs. 1.49+/-0.07 mL min(-1) g(-1) in subepicardial and subendoca rdial layers in the LAD perfused region) suggests that increased diast olic creep increased metabolic demands. This study indicates that pass ive stretching of the ischaemic area during coronary artery occlusion is an important mechanism behind diastolic creep.