CAVAL OCCLUSION ALTERS THE SHAPE OF THE ISCHEMIC AND NONISCHEMIC PRESSURE-LENGTH LOOP

Objectives: The effects of changes in preload on paradoxical myocardia l wall motion during ischemia have been previously studied. However, t he studies have been performed using slow volume changes. It was decid ed to study the effects of fast changes in preload, which would occur during caval occlusion, on the regional pressure-length loops during i schemia. Design: Retrospective trial. Setting: Experimental animal lab oratory in a university medical center. Participants: Ten anesthetized adult dogs. Interventions:ln an open chest preparation, regional isch emia was achieved by occluding the left anterior descending coronary a rtery for 10 minutes, with sudden caval occlusions being performed to assess the influence of preload on wall motion. Measurements and Main Results: Left ventricular pressure and regional segmental lengths were measured. During caval occlusion, beat by beat, percent postsystolic shortening and percent systolic bulging in the ischemic region, percen t isovolumetric shortening in the nonischemic region, and percent syst olic shortening in both regions were calculated. Caval occlusion signi ficantly decreased the end-diastolic pressure (12.62 +/- 1.02 to 3.39 +/- 0.59 mmHg) and length. in the ischemic area, although systolic sho rtening became more negative(-1.8 +/- 0.79% to -9.65 +/- 1.08%), posts ystolic shortening (9.66 +/- 0.73% to 15.53 +/- 1.2%) and systolic bul ging (4.6 +/- 0.49% to 12.67 +/- 1.04%) increased. In the nonischemic area, systolic shortening decreased slightly but significantly (18.01 +/- 3.24% to 14.93 +/- 3.64%) as isovolumetric shortening increased (2 .77 +/- 0.68 to 7.37 +/- 1.29%). Caval occlusion increased the rightwa rd shift and accentuated the distortion of the ischemic loop. The noni schemic loop displayed a leftward shift of the systolic isovolumetric component and a slight decrease in percent total length change. Conclu sion: Caval occlusion modifies the shape of the pressure-length loop o f the ischemic myocardium. This change in shape may interfere with the assessment of regional systolic indexes obtained by caval occlusion i n ischemic hearts. Copyright (C) 1997 by W.B. Saunders Company.