Experimental myocardial infarction. XVI. The detection of inotropic contractile reserve with postextrasystolic potentiation in acutely ischemic canine myocardium

Abstract

Postextrasystolic potentiation after a single closely coupled extrasystole may identify residual ventricular contractile performance in acutely ischemic myocardium without producing sustained secondary ischemic depression of myocardial function. Postextrasystolic potentiation was systematically used in eight open chest dogs to assess the progression of regional contraction abnormalities during a 10 minute occlusion of the left anterior descending coronary artery. Segment function was determined from pressure-length loop areas inscribed during right ventricular pacing at 128 +/- 3 (mean +/- standard error of the mean) beats/min, and after single closely coupled (179 +/- 3 msec) extrasystoles. Despite a 50 percent decrease in border zone segment function, postextrasystolic potentiation consistently augmented mechanical performance to control levels throughout the ischemic period. Central ischemic zone segment function deteriorated more profoundly, with the development of holosystolic aneurysmal bulging within 30 seconds after occlusion. Nonetheless, postextrasystolic potentiation produced marked inotropic augmentation, but not to control levels, for up to 10 minutes of ischemia. These results suggest that latent viability and contractile reserve may exist during brief periods of coronary occlusion.