Effects of Selective Coronary Hypotension on Regional Myocardial Blood Flow of Dog Papillary Muscle

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Abstract
This study is designed to investigate whether a selective hypotension of the left circumflex coronary artery (LCCA) causes selectively increased ischemia in the posterior papillary muscle (PPM-L) of the dog. Regional myocardial flow was measured by Rb86 clearance technique. In control animals, the distribution of blood flow between subendocardium and subepicardium, between the left and right ventricles and the septum, and between the free wall and the papillary muscle was studied. In normal situation, the subendocardial to subepicardial flow ratio of the left and right ventricle was approximately unity, however, in the papillary muscle the subendocardial perfusion was less than that of the central core. In selective LCCA hypotension by partial obstruction, the subendo/central core flow ratio of the PPM-L increased in contrast to a marked decrease of subendo/subepi flow ratio of the left ventricular free wall. The ratio of blood flow in the ischemic PPM-L and/or posterior wall of the left ventricle to that in the normally perfused anterior wall of the left ventricle dropped profoundly when LCCA is sufficiently narrowed to cause a pressure drop in the distal portion of the vessel. The flow drop in the PPM-L was greater than that in the other part of the subendocardium. These results demonstrated a selective impairment of blood flow to the posterior papillary muscle after partial obstruction of the left circumflex artery which may have direct clinical relevance.