Left ventricular geometry during partial and complete coronary occlusion in the conscious dog

Seven dogs were instrumented with a left ventricular micromanometer and pairs of ultrasonic crystals to measure left ventricular wall thicknesses (control and ischemic regions) and short and long left ventricular axes; cuff occluders were placed around the left circumflex coronary artery and the inferior vena cava. Measurements were performed at rest, after 2 min of partial and complete coronary occlusion, and 1 and 10 min after release of partial and complete coronary occlusion. Left ventricular wall thickness in the ischemic region showed reduced systolic thickening during partial coronary occlusion and systolic thinning during complete coronary occlusion. During diastole, at zero pressure (inferior vena cava obstruction) the left ventricular short axis was unchanged during partial coronary occlusion but significantly increased (creep) during complete coronary occlusion (P less than 0.05), whereas after release of both partial and complete coronary occlusion the short axis at zero pressure decreased significantly (P less than 0.025). Left ventricular wall thickness at zero diastolic pressure in the ischemic region was significantly thinner during complete coronary occlusion than during control and significantly thicker (reactive hyperemia) 1 min after release of both partial and complete coronary occlusion. The long left ventricular axis remained unchanged during the entire experiment. At end-diastole, the long/short axis ratio was normal during partial (1.72; control 1.68; NS) and complete coronary occlusion (1.69; NS), but it decreased significantly from control of 2.10 to 1.99 with partial coronary occlusion and 1.85 with complete coronary occlusion (P less than 0.01). The changes in the L/S ratio during partial and complete coronary occlusion were proportional to changes in left ventricular chamber volume (correlation coefficient 0.94). Our data show that left ventricular shape remains normal at end-diastole during partial and complete coronary occlusion but becomes significantly more spherical at end-systole, with reduction of the normal tendency for the ventricle to become more elliptical during systole. These elliptical and spherical shape changes of the left ventricle during partial and complete coronary occlusion appear to be closely related to the chamber volume.