Investigation of the efficacy of pharmacologic agents affecting
myocardial infarct size after coronary artery occlusion is complicated by the variability of collateral flow among experimental animals which results in variability of
infarct size. To overcome this difficulty, we developed an autoradiographic method to delineate the ischemic area at risk of
necrosis after coronary artery occlusion and we invetigated the potential protective effect of a
calcium antagonist
verapamil. The left anterior descending coronary arteries of 25
barbiturate-anesthetized dogs were occluded. Thirty minutes later, highly radioactive
human albumin microspheres labeled with 99mTc were injected into the left atrium. One hour after coronary artery occlusion, dogs were randomized to control or treated groups; the latter received a 0.2 mg/kg loading dose and 0.6 mg/kg per hr maintenance dose of
verapamil intravenously. Eight hours after coronary artery occlusion, the dogs were killed, the hearts were excised, and the left ventricle was sectioned parallel to the atrioventricular groove;
infarct size was determined planimetrically after incubation in triphenyl tetrazolium
chloride. The slices were then exposed to high-speed
x-ray film with image-enhancing screens. The percentage of left ventricle that was ischemic, as determined by planimetry of autoradiographs, was similar in treated and control animals (36.6 +/- 2.0% compared to 37.3 +/- 2.8%, respectively). Of the ischemic area, 92.0 +/- 4.3% was infarcted in control animals and 70.5 +/- 5.1% was infarcted in treated animals (P < 0.01). Thus, this autoradiographic method using 99mTc-labeled
human albumin microspheres is useful in delineating the area of
ischemia after coronary artery occlusion and in evaluating the efficacy of pharmacologic agents designed to protect ischemic myocardium.
Verapamil, administered 1 hr after coronary artery occlusion, is effective in limiting
infarct size.