Innate protection of baboon myocardium: Effects of coronary artery occlusion and reperfusion

To determine whether the extent of myocardial infarction differs in conscious baboons and pigs, both devoid of preformed collaterals, the effects of 40 and 90 min of coronary artery (CA) occlusion (O) both followed by 4-7 days of CA reperfusion (R) were examined in both species. CAO reduced subendocardial and subepicardial blood flows similarly, almost to zero, in baboons and pigs for the entire CAO period. At 24 h of CAR, subendocardial blood flow had almost returned to pre-CAO control levels in baboons but remained significantly depressed in pigs. The major difference in hemodynamics during CAO and CAR was in left ventricular end-diastolic pressure, which rose by 6 ± 1 mmHg in pigs over the initial 24-h reperfusion period but did not change significantly in baboons. These data on recovery of subendocardial blood flow and left ventricular end-diastolic pressure suggest larger infarcts in pigs than in baboons. Indeed, infarct size expressed as a function of area at risk (IF/AAR) was significantly greater (P < 0.05) in pigs (53 ± 4.9%) than in baboons (17 ± 2.9%) with 90 min of CAO and 4-7 days of CAR. With 40 min of CAO and 4-7 days of CAR, IF/AAR was 46 ± 3.6% in pigs, whereas in baboons the IF/AAR was minimal, i.e., 2 ± 0.6%. Thus pigs and baboons were characterized by minimal coronary collateral circulation, but infarct size was significantly less in conscious baboons than in conscious pigs. Potentially, these differences could be explained, in part, by natural protective mechanisms and/or less reperfusion injury in primates. These results in primates may also help explain the salutary effects of CAR in patients at intervals longer than have been demonstrated to be beneficial in other experimental animals.