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Postextrasystolic potentiation was studied during control and 5 minutes after coronary occlusion in epicardial regions of 12 open-chest dogs. Segmental behavior evaluated with ultrasonic crystals was correlated with regional myocardial blood flow (MBF) measured with radioactive microspheres. A similar correlation was found between the percentage of systolic shortening in postextrasystolic beats and MBF in epicardial (r = 0.64) and endocardial (r = 0.97) regions, although the scatter was much larger in the epicardium. The correlation was similar when segmental function was expressed as the area of the pressure-segment length loop. Three types of segments were described; completely ischemic segments (transmural MBF less than 5% of control), in which end-systolic length was larger than end-diastolic length after postextrasystolic potentiation; severely ischemic segments (5% less than or equal to transmural MBF less than 25% of control), in which the ischemic bulge during control beats was replaced by active shortening after premature ventricular complexes; and marginal segments (25% less than or equal to transmural MBF less than 100% of control), in which depressed shortening was enhanced close to control after a premature ventricular complex. These data reconcile conflicting studies, which did not consider similar degrees of ischemia and show a rapid loss of postextrasystolic potentiation in completely ischemic segments.

circulation

Relations between myocardial blood flow and postextrasystolic potentiation in epicardial and endocardial left ventricular regions early after coronary occlusion in dogs.