Effects of acute left anterior descending occlusion on regional myocardial blood flow and wall thickening in the presence of a circumflex stenosis in dogs.

In this study, 2 hypotheses were tested: (1) Myocardium supplied by a stenosed circumflex coronary artery (LC) does not demonstrate compensatory increases in regional blood flow and systolic thickening when the left anterior descending coronary artery (LAD) is acutely occluded. (2) Blood flow to myocardium in the distribution of an acutely occluded LAD is lower in the presence of a stenosed than in the presence of an unstenosed LC. Fifty-three open-chest, anesthetized dogs were studied. Regional coronary blood flow (8 to 10-mu microspheres) and wall thickening (sonomicrometer crystals) were measured before and after LAD occlusion in the presence of an unstenosed LC artery, and a moderate and severe LC stenosis. Acute LAD occlusion in the presence of an unstenosed LAD was not accompanied by a significant increase in regional blood flow to the remote LC bed; posterior myocardial wall thickening, however, increased from 0.22 +/- 0.02% to 0.24 +/- 0.02% (p = 0.04). In the presence of a moderate LC stenosis (gradient 29 +/- 1 mm Hg), LAD occlusion was associated with a 9% (p = 0.02) decrease in endocardial flow and an 11% decrease in the endocardial/epicardial flow ratio (p = 0.002). Transmural flow was unchanged and there was no compensatory increase in posterior wall thickening. In the presence of a more severe LC stenosis (gradient 49 +/- 1 mm Hg), central LC endocardial flow decreased by 32% (p = 0.0008) at the time of LAD occlusion. Similar alterations were noted in the peripheral LC region.(ABSTRACT TRUNCATED AT 250 WORDS)