Functional consequences of acute anterior vs. posterior wall ischemia in canine left ventricles

We compared the consequences of acute anterior and posterior wall ischemia on regional left ventricular function in seven open-chest dogs. Circumferentially oriented sonomicrometers were implanted in the midwall of the anterior and posterior left ventricle. The left anterior descending (LAD) and left circumflex (LCX) coronary arteries were each occluded for 3 min, with 45 min of reperfusion between the two occlusions. The ischemic areas at risk, as assessed by postmortem perfusion techniques, were similar for anterior (34.5 +/- 12.5 g) and posterior (32.3 +/- 9.4 g) wall ischemia. Both occlusions produced a similar increase in end-diastolic pressure. After LAD occlusion, total segment shortening (end diastole to aortic valve closure) in the nonischemic posterior wall increased from 8.0 +/- 3.9 to 10.8 +/- 4.4%, solely caused by increased isovolumic shortening. In contrast, with LCX occlusion, total segment shortening in the nonischemic anterior wall increased significantly more, from 10.5 +/- 3.8 to 14.6 +/- 4.2% caused by nearly equal increases in isovolumic and ejection phase shortening. Thus, with both LAD and LCX occlusions, there was increased shortening in nonischemic areas during isovolumic systole, which was "wasted" in paradoxically stretching the ischemic zone. However, a compensatory increase in nonischemic area ejection phase shortening occurred only with LCX occlusions. These findings may explain the greater functional impairment that occurs with LAD than LCX occlusions.