Effectiveness of dipyridamole in reducing the size of experimental myocardial infarction.

Abstract

The role of vasodilators in reducing the extent of myocardial necrosis after acute coronary occlusion is controversial. The efficacy of dipyridamole in reducing infarct size 8 or 24 h after ligation of the left anterior descending (LAD) coronary artery in 12 dogs was evaluated. On the basis of identical epicardial ST-segment elevations 15 min after coronary ligation, the dogs were divided equally into control or dipyridamole-treated (3 mg/kg) groups. 99mTc-glucoheptonate (TcGH) was injected i.v. 1 h after coronary occlusion and myocardial imaging performed before autopsy. Blood pressure (BP), heart rate (HR), left ventricular end-diastolic pressure (LVEDP) and left ventriculography (VG) were recorded before and at regular intervals after LAD occlusion. Autopsy delineation of myocardial infarct size was determined by planimetry of myocardial slices stained with nitroblue tetrazolium (NBT) and in vivo infarct size was measured by planimetry of myocardial TcGH uptake in the right anterior oblique view. During the infusion of dipyridamole, mean BP fell in the dipyridamole group from 102 .+-. 4 to 80 .+-. 6 mm Hg (P < 0.05) (mean .+-. SEM [SE of mean]), HR decreased from 134 .+-. 5 to 122 .+-. 5 beats/min (P < 0.05), tension-time index decreased from 3120 .+-. 296 to 1839 .+-. 211 mm Hg-s/min (P < 0.05) and LVEDP was unchanged, 7.7 .+-. 0.6 vs. 7.9 .+-. 0.9 mm Hg (NS [not significant]). VG analysis 1 h after coronary occlusion revealed less decrease in regional ejection fraction in the anterior wall of dipyridamole-treated animals compared with the control group, -11 .+-. 3% vs. -33 .+-. 5% (P < 0.01); inferior wall ejection fraction increased in both groups, but more in dipyridamole-treated animals, 30 .+-. 3% vs. 20 .+-. 5% (P < 0.05). The radionuclide uptake of TcGH was smaller in dipyridamole compared with control animals, 7.9 .+-. 0.9 vs. 16.7 .+-. 1.0 cm2 (P < 0.025), while autopsy-determined infarct weight (NBT technique) was also less, 7.7 .+-. 1.2 vs. 17.6 .+-. 1.4 g (P < 0.025). Dipyridamole can favorably alter the course of acute experimental myocardial infarction. The decrease in infarct size can be quantified in vivo and noninvasively by TcGH myocardial imaging and verified postmortem by the NBT histochemical staining technique.