Studies in the Pathology of Vascular disease: Studies on Experimental Coronary Occlusion

Anatomical studies of the dog heart after experimental occlusion of the descending ramus of the left coronary artery show that histo-logical evidence of necrosis of the muscle fibers is first evident 7 to 9 hours after the occlusion, at which time a hemorrhagic infarct develops. Organization of the necrotic tissue manifests itself on the fourth day and complete replacement by fibrous tissue scar occurs by the end of a month.'"0 Such findings, however, give little indication of the functional changes in the myocardium following the development of anoxemia. To study these an optical myograph of small size which recorded contraction of a small segment of muscle from the ventricular surface was devised.1' By recording myo-graphic curves and aortic or ventricular pressure curves (with calibrated optical manometers) simultaneously, records of muscle contraction and relaxation in relation to the phases of the cardiac cycle were obtained. Normal myograms, although slightly distorted by oscillations during the isometric contraction and relaxation phases, clearly showed the natural shortening which occurs during systolic ejection and the lengthening which follows isometric relaxation. Following occlusion of the descending ramus of the left coronary artery an evoluting series of changes in the myogram was observed which indicated a progressive enfeeblement of contraction to the extent that within a minute after occlusion the zone of ischemic muscle was stretched during isometric contraction, remained stretched during systolic ejection, and shortened quickly during isometric relaxation. In brief, muscular contraction in the ischemic zone was abolished within a minute after occlusion and the stretching and shortening of the affected fibers followed passively the changes in the intraventricular pressure. When circulation was restored by release of the ligatures after short intervals of occlusion (10 minutes or less) a reversed series of changes occurred in the myogram with restoration of normal vigorous contraction in the part. In one experiment where the period of ligation was 23 minutes recovery of contraction had not occurred two hours after restoration of circulation at which time the experiment was terminated.