NEGATIVE INOTROPIC EFFECT OF PROPRANOLOL IS ATTENUATED IN UNDERPERFUSED FELINE HEART WITH AN ACUTE ISCHEMIC REGION

Beta-Adrenergic blockade alleviates myocardial ischemia, probably larg ely through heart rate (HR) reduction. We hypothesized that the negati ve inotropic effect of beta-blockade, which is believed to be potentia lly dangerous, is attenuated in underperfused hearts with an acute cor onary artery occlusion. We studied the effect of intravenous propranol ol(l mg/kg i.v.) in feline hearts with acute circumflex coronary arter y (LCX) occlusion by cross-oriented segments in normally perfused and mildly underperfused left ventricular (LV) anterior wall. A control gr oup (n=10) was compared with a stenosis group (n=9) in which the mean coronary perfusion pressure was reduced (91+/-4 g vs. 136+/-5 mm Hg, p <0.01). End-systolic pressure-length (ESP-ESL) relations during dynami c afterload increase and preload reduction were calculated to evaluate regional inotropy. HR and LV peak systolic blood pressure (LVSP) decr eased in both groups after beta-blockade (p<0.05). Subendocardial and mid-myocardial blood flow measured by radiolabeled microspheres decrea sed in the control group (p<0.05) but was unchanged in the stenosis gr oup. Systolic shortening of circumferential segments also decreased in the control group (p<0.05) but was unchanged in the stenosis group. E SP-ESL relations of circumferential segments shifted markedly rightwar d in the control group, whereas a modest rightward shift was noted in the stenosis group. This study in feline heart with acute LCX occlusio n showed an attenuated negative inotropic effect of beta-blockade in u nderperfused LV anterior wall.