Impaired Function of Salvaged Myocardium: Iwo-dimensional Echocardiographic Quantification of Regional Wall Thickening in the Open-chest Dog

This study was designed to examine the functional properties of myocardium subjected to acute coronary occlusion but surviving the ischemic insult. Ten conscious mongrel dogs underwent midcircumflex coronary occlusion and were treated for 6 hours with prostacyclin, 540 ng/kg/min, and ibuprofen, 110 puglkg/min, or dipyridamole (7-9.7 gg/kg/min). At 7 days, each dog was anesthetized, the chest was opened, and cross-sectional two-dimensional echocardiograms were obtained through the middle of the occluded vascular bed. A computer-aided contouring system was used to assess percent systolic thickening in 16 equally spaced segments around the left ventricle. Metal markers sewn to the epicardium permitted precise regional correlation of histology, percent systolic thickening, and flow, as measured by radioactive microspheres. Necrosis was minimal, averaging only 2.2 + 0.8% (± SEM) of the left ventricular ring corresponding to the echocardiographic cross section. Percent systolic thickening was 28.6 + 4.7 in the nonischemic anterior wall, but was reduced to -4.5 + 3.1 in the occluded bed (p < 0.01). In individual echo segments, percent systolic thickening correlated with local flow (r = 0.69, p < 0.001), but was still depressed even when flow was normal. In six segments within the occluded bed that had normal histology and flow, percent systolic thickening was 52% less than that in the nonischemic region (p < 0.02). Thus, coronary artery occlusion combined with drug treatment results in myocardium that, although histologically normal and supplied by normal myocardial blood flow, remains functionally abnormal 7 days after occlusion.