Effects of a cardiac glycoside in combination with propranolol on the ischemic heart of conscious dogs

The effects of coronary occlusion and of subsequent propranolol and ouabain administration were examined in 12 conscious dogs. Overall left ventricular (LV) function was assessed by measurement of LV pressure and dP/dt, and regional myocardial function was assessed by measurements of segment length (SL), velocity of SL shortening and regional myocardial "work," i.e., pressure-length loops in normal and moderately and severely ischemic zones. Regional intramyocardial electrograms were measured at the same sites as function along with regional myocardial blood flow as determined by the radioactive microsphere technique. Coronary occlusion resulted in graded loss of function from the normal to severely ischemic zones, along with graded flow reductions and graded elevation of the ST segment. Propranolol, 1 mg/kg, depressed overall LV function and function in the normal zone more than in ischemic zones. Propranolol reduced flow to the normal zone and increased flow to ischemic zones, while not affecting ST-segment elevation significantly. In the presence of occlusion and propranolol, ouabain, 20 microgram/kg, improved overall LV function as well as regional function in the normal, moderately ischemic and severely ischemic zones. In addition, ouabain reduced ST elevation and increased blood flow further in moderately and severely ischemic zones. Most strikingly, ouabain returned normal systolic shortening to eight severely ischemic segments which were previously akinetic.