Improved myocardial protection with propranolol during induced ischemia

Propranolol has been suggested as a useful agent for protecting the myocardium during both regional and global ischemia. An isolated, isovolumic feline heart model was used to assess the effectiveness of propranolol in providing myocardial preservation during normothermic and hypothermic global ischemia. Normothermic ischemia was induced for 30 minutes with eight hearts receiving 100 μg of propranolol at the onset of ischemia and eight receiving none. Fourteen of 28 hearts subjected to 60 minutes of hypothermic ischemia received 100 μg of propranolol, whereas the remaining 14 received none. All hearts had 45 minutes of normothermic reperfusion. Ventricular function was assessed by measuring left ventricular developed pressure (DP) and maximum dP/dt. Myocardial metabolic activity was monitored by continuously measuring myocardial oxygen and carbon dioxide tension (PmO ₂ and PmCO ₂) by mass spectrometry. Biopsy specimens were taken at the end of reperfusion for estimation of the myocardial water content and morphologic assessment using both light and electron microscopy. With both normothermic and hypothermic ischemia, the administration of propranolol resulted in significantly better recovery of ventricular function. Similarly, hearts that received propranolol at the onset of ischemia developed less edema. Although no difference was noted in the rate of rise of PmCO ₂ during ischemia in the hypothermic hearts, the peak reached during early reperfusion was lower and the rate of fall faster in hearts given propranolol. Morphologic preservation was improved with propranolol in both the normothermic and hypothermic groups. These results show that propranolol exerts a significant protective effect in hearts subjected to either normothermic or hypothermic global ischemia.