Relations between 2-dimensional echocardiographic wall thickening abnormalities, myocardial infarct size and coronary risk area in normal and hypertrophied myocardium in dogs

Abstract

Systolic wall thickening abnormalities are sensitive indicators of ischemia and infarction. One purpose of this investigation was to assess the relation between coronary risk area, infarct size and wall thickening abnormalities (dyskinesia) using 2-dimensional echocardiography (2-D echo) in a closed-chest conscious dog model of acute myocardial infarction. The second purpose was to study the effects of systemic hypertension (SH) and left ventricular (LV) hypertrophy on these relations. Our hypothesis was that the infarct size and the extent of 2D echocardiographic dyskinesia would be quantitatively different in SH-LV hypertrophy, a condition in which coronary vascular reserve is diminished. Permanent circumflex coronary occlusion was performed in 15 conscious normal dogs and in 14 dogs with LV hypertrophy secondary to renal hypertension. Two-dimensional echocardiograms were obtained before, 20 minutes after and 2 days after coronary occlusion. The systolic wall thickening along 12 equidistant radii was analyzed in short-axis images. Percent dyskinesia on 2-D echo was defined as the percentage of radii showing systolic thinning. Infarct size was determined pathologically and risk area was determined angiographically. For a given risk area, coronary occlusion resulted in a larger infarction in dogs with SH-LV hypertrophy than in normal dogs (p <0.05). Two-dimensional echocardiographic dyskinesia correlated well with infarct size both at 20 minutes r = 0.92) and 2 days (r = 0.94); dyskinesia modestly overestimated the infarct size and underestimated the risk area. The relations were similar in both normal and SH-LV hypertrophy groups. Infarctions that did not produce dyskinesia were very small (≤4% LV mass at 20 minutes and ≤6% LV mass at 2 days). In all but 3 dogs, dyskinesia at 20 minutes persisted at 2 days. In no dog did dyskinesia develop at 2 days if it was absent at 20 minutes. Thus, 2-D echo-demonstrated wall thickening abnormalities may be useful in the quantitative assessment of infarct size and coronary risk area.