Decreased systolic wall thickening in myocardium adjacent to ischemic zones in conscious swine during brief coronary artery occlusion.

The purpose of this study was to examine wall thickening in normally perfused myocardium adjacent to acutely ischemic zones. Regional wall thickening (%WT), internal minor axis diameter, and hemodynamics were monitored in nine conscious swine during temporary occlusion of the left circumflex coronary artery (LCCA). Animals were chronically instrumented with ultrasonic dimension gauges for measuring left ventricular (LV) wall thickness and minor axis, catheters in the left atrium and aorta, and a pneumatic occluder around the proximal LCCA. During a 2-minute occlusion of the LCCA, radiolabeled tracer microspheres (10 micron) were injected into the left atrium to determine regional myocardial blood flow (RMBF). Within the ischemic zone, reduction of %WT was related linearly (Y = 24.9 X -4.1, p less than 0.001) to reduced RMBF and endocardial/epicardial blood flow ratio was reduced from 1.30 +/- 0.12 (mean +/- SE) to 0.87 +/- 0.11 (p less than 0.01). In zones adjacent to the ischemic zones RMBF was unchanged by LCCA occlusion. RMBF and %WT were poorly correlated (r = 0.38) and endocardial/epicardial blood flow ratio was unchanged from preocclusion values. Therefore, myocardium adjacent to ischemic zones may have reduced thickening despite no apparent blood flow changes. We conclude that such dysfunction may be due to either mechanical tethering effects or a reduction of global LV function due to the presence of an acutely ischemic zone.