Gradients of epicardial strain across the perfusion boundary during acute myocardial ischemia.

To study the mechanical interaction between acutely ischemic and adjacent perfused myocardium, nonhomogeneous distributions of end-systolic epicardial strain were measured using an array of radiopaque beads sewn on the left ventricular free wall of the pig during complete left circumflex coronary artery occlusion. The midwall perfusion boundary, demarcated by postmortem dye injection, was reconstructed over the span of the epicardial array. During ischemia, circumferential and longitudinal shortening remained significantly depressed up to 13 mm outside the ischemic region near the base of the ventricle, up to 8-9 mm at the midventricle, but only 0-1 mm near the apex (P < 0.05). Gradients of circumferential and longitudinal strain across the boundary were significantly different during both baseline conditions and acute ischemia (P = 0.0001). However, gradients of the change in the strain from baseline to ischemia were not different for the two components. These results support the concept that direction-dependent differences in the strain gradients across the boundary during ischemia were due to the preservation of the baseline regional variations of strain combined with a loss of systolic function in the ischemic region.