Relations Between Myocardial Blood Flow and Postextrasystolic Potentiation in Epicardial and Endocardial Left Ventricular Regions

Postextrasystolic potentiation was studied during control and 5 minutes after coronary occlusion in epicardial and endocardial regions of 12.open-chest dogs. Segmental behavior evaluated with ultrasonic crystals. was correlated with regional myocardial blood flow (MBF) measured with radioactive inicrospheres. 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: cotmpletely ischemic segments (transmural MBF < 5% of control), in which end-systolic length was larger than end-diastolic length after postextrasystolic potentiation; severely ischemic segments (5% < transmural MBF < 25% of control), in which the ischemic bulge during control beats was replaced by active shortening after premature ventricular complexes; and marginal segments (25% <, transmural MBF < 100% of control), in which depressed shortening was enhanced xlose 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.