An Analysis of Segmental Ischemic Dysfunction Utilizing the Pressure-Length Loop

Left ventricular (LV) pressure and myocardial segment length, determined by an epicardial mercury-in-silastic length gauge, were plotted simultaneously to obtain a pressure-length loop before and after left anterior descending artery (LAD) occlusion in 11 dogs. Previous studies have indicated that the area within this loop is a sensitive and reproducible means of quantitating regional myocardial performance. Immediately following ligation, systolic performance deteriorated as indicated by progressive reduction in the pressure-length loop area. Within approximately 30 sec a zero area for the pressure-length loop was observed, indicating no effective work was being performed by the ischemic segment. During the ensuing 3-5 min the pressure-length loop moved into a clockwise orientation which indicated work was being done on rather than by the segment. The magnitude was approximately 50% of that amount previously generated by the segment. In addition, during this latter period of repetitive passive stretch, the end-diastolic pressure-length relationship shifted to the right indicating increased diastolic compliance. Restoration of perfusion after 30 min produced variable results. Substantial return of function was observed in two animals, but recovery in the majority of animals was limited to the elimination of paradoxical expansion without restoration of active contraction. Therefore, the pressure-length loop method allows quantitation of regional myocardial performance, and indicates that a predictable pattern of significant changes in both systole and diastole accompanies acute myocardial ischemia.