Functional abnormalities in nonoccluded regions of myocardium after experimental coronary occlusion

Abstract

The performance characterstics of both ischemic and “adjacent” and “remote” nonischemic myocardium were studied in open chest dogs by three mercury-in-Silastic length gauges sutured to the anterior surface of the left ventricle before and after occlusion of the distal left anterior descending coronary artery. The adjacent gauge was separated from the ischemic segment by one large nonoccluded diagonal branch of the left anterior descending artery. Remote myocardium was separated from the ischemic area by two such branches. At the time of occlusion epicardial S-T segment elevation appeared in the ischemic region but not in the adjacent or remote regions. Immediately after occlusion, typical changes of ischemic dysfunction appeared. Late systolic lengthening, depression of systolic shortening and increased diastolic compliance occurred consistently and simultaneously in ischemic and adjacent regions and inconsistently in the remote region. Five minutes after occlusion, fiber shortening was depressed to 21, 58 and 67 percent of control values in ischemic, adjacent and remote regions, respectively. Heart rate did not change, and mean arterial pressure decreased slightly. These changes persisted over time. In 11 of these dogs, end-diastolic pressure was maintained constant 20 minutes after occlusion. Systolic shortening was depressed to 40 and 74 percent of control values in the ischemic and adjacent regions, respectively. In six dogs, end-diastolic pressure was varied from 5 to 20 mm Hg by rapid volume loading during the control state and 30 minutes after occlusion. Systolic shortening in ischemic, adjacent and remote regions was depressed to 20, 40 and 65 percent of control values, respectively. The severity of all functional alterations after coronary occlusion was directly related to proximity to the ischemic region. These results indicate that depression of left ventricular function after coronary occlusion may be partially related to previously unrecognized depression of function in apparently “nonischemic” myocardium.