Caval occlusion alters the shape of the ischemic and nonischemic pressure-length loop

Abstract

Objectives: The effects of changes in preload on paradoxical myocardial wall motion during ischemia have been previously studied. However, the studies have been performed using slow volume changes. It was decided to study the effects of fast changes in preload, which would occur during caval occlusion, on the regional pressure-length loops during ischemia. Design: Retrospective trial. Setting: Experimental animal laboratory in a university medical center. Participants: Ten anesthetized adult dogs. Interventions: In an open chest preparation, regional ischemia was achieved by occluding the left anterior descending coronary artery 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, percent isovolumetric shortening in the nonischemic region, and percent systolic shortening in both regions were calculated. Caval occlusion significantly decreased the end-diastolic pressure (12.62 ± 1.02 to 3.39 ± 0.59 mmHg) and length. In the ischemic area, although systolic shortening became more negative (−1.8 ± 0.79% to −9.65 ± 1.08%), postsystolic shortening (9.66 ± 0.73% to 15.53 ± 1.2%) and systolic bulging (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 rightward shift and accentuated the distortion of the ischemic loop. The nonischemic loop displayed a leftward shift of the systolic isovolumetric component and a slight decrease in percent total length change. Conclusion: Caval occlusion modifies the shape of the pressure-length loop of the ischemic myocardium. This change in shape may interfere with the assessment of regional systolic indexes obtained by caval occlusion in ischemic hearts.