Abstract
The effects of propranolol (0.5-2mg./Kg.) and isoproterenol (0.2μg./Kg./min.) on the severity and extent of ischemic injury after acute coronary occlusion in experimental dogs were determined from the average S-T segment elevation (E-ST) and the number of sites where S-T elevation exceeded 2mV. (N-ST) in 12 to 20 left ventricular (LV) epicardial sites. The mappings were obtained 15min. after repetitive occlusions of a main branch of the left anterior descending coronary artery. In 5 dogs propranolol decreased E-ST from 4.0±0.8 during simple control occlusion to 1.5±0.3mV. (SEM) (p<0.01) and N-ST from 9.2±1.0 to 4.2±0.5 (p<0.01). At this time, LV myocardial contractility expressed by dP/dt/IIT decreased from 2, 320±280 to 1, 460±230 (p<0.01) along with significant reduction of cardiac output (CO). LV developed tension assessed from LV TTI/min. fell slightly and insignificantly. In contrast, in 5 dogs the infusion of isoproterenol increased E-ST from 1.5±0.2 to 3.1±0.7mV. and N-ST from 6.6±0.6 to 9.4±1.1 (both, p<0.01). The value of dP/dt/IIT increased from 1, 980±440 to 4, 610±920 (p<0.01) with concomitant increment in CO. LV TTI/min. elevated slightly and again insignificantly. It was concluded that, in beating in situ heart the severity and extent of acute myocardial ischemic injury can be altered by the changes in LV contractile state, even in the absence of changes in LV wall tension.
