Negative inotropic effect of propranolol is attenuated in underperfused feline heart with an acute ischemic region.

Abstract

beta-Adrenergic blockade alleviates myocardial ischemia, probably largely through heart rate (HR) reduction. We hypothesized that the negative inotropic effect of beta-blockade, which is believed to be potentially dangerous, is attenuated in underperfused hearts with an acute coronary artery occlusion. We studied the effect of intravenous propranolol (1 mg/kg i.v.) in feline hearts with acute circumflex coronary artery (LCX) occlusion by cross-oriented segments in normally perfused and mildly underperfused left ventricular (LV) anterior wall. A control group (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 dynamic afterload increase and preload reduction were calculated to evaluate regional inotropy. HR and LV peak systolic blood pressure (LVSP) decreased in both groups after beta-blockade (p < 0.05). Subendocardial and mid-myocardial blood flow measured by radiolabeled microspheres decreased in the control group (p < 0.05) but was unchanged in the stenosis group. Systolic shortening of circumferential segments also decreased in the control group (p < 0.05) but was unchanged in the stenosis group. ESP-ESL relations of circumferential segments shifted markedly rightward in the control group, whereas a modest rightward shift was noted in the stenosis group. This study in feline heart with acute LCX occlusion showed an attenuated negative inotropic effect of beta-blockade in underperfused LV anterior wall.