The inability of isoproterenol or propranolol to alter the lateral dimensions of experimentally induced myocardial infarcts.

The relationship between the blood flow pattern immediately following coronary artery occlusion and the resulting infarct 24 hours later was studied in dogs treated with isoproterenol (0.5 micrograms/kg/min for 2 hours) or with propranolol (2 mg/kg every 6 hours). The coronary artery of a closed chest dog was perfused via a special cannula with arterial blood. A 2-mm diameter plastic bead was introduced into the perfusate to embolize a coronary branch. One minute after occlusion, radiolabelled microspheres were injected into the perfusate. The dogs were then allowed to recover. 24 hours later the dogs were reanesthetized and their hearts removed. The hearts were sliced into 4 mm thick sections and the microsphere distribution was visualized by autoradiography of the tissue. Superimposition of developed autoradiographs and tracings of the infarct pattern of stained sections allowed direct comparison of the blood flow pattern immediately after occlusion to the eventual pattern of infarction. In all 8 control dogs, all 6 isoproterenol dogs and all 12 propranolol dogs the lateral borders of blood flow and infarction were superimposable indicating no lateral change in infarct size resulting from treatment. In the control group there was a subepicardial region of the ischemic zone which did not infarct (15.2 +/- 2.3% of the ischemic zone). Though isoproterenol did not significantly change the size of this zone, propranolol increased it to 35.9 +/- 6,5% (p less than 0.005) indicating vertical but not lateral salvage.