Hyperkinetic contraction of a nonischemic segment of ischemic left ventricle in anesthetized dogs

Regional myocardial function during acute coronary artery occlusion was studied with ultrasonic dimension gauges in 20 open-chest anesthetized dogs. Two pairs of ultrasonic crystals were implanted in the left ventricular free wall near the epicardium in an ischemic segment and in a control nonischemic segment, and the segment length (SL) and maximum velocity of systolic shortening (max dL/dt) were measured. In six dogs, the wall thickness (WT) was measured simultaneously in the same regions with sonomicrometry. Left ventricular pressure (LVP), aortic pressure (AoP), and plasma norepinephrine concentration in the coronary sinus (NECS) were also measured. The heart rate was kept constant (180 beats/min) with atrial pacing. The left anterior descending coronary artery was occluded at its distal portion without propranolol in 12 dogs (group 1) and 30 min after propranolol in eight dogs (group 2). In the ischemic region, coronary artery occlusion resulted in an increase in end-diastolic SL (50% at 3 min after occlusion in group 1, P less than 0.005), and a decrease in max dL/dt in systole (36% at 5 min after occlusion in group 1, P less than 0.02). In the nonischemic region, end-diastolic SL did not change significantly, but an increase in max dL/dt (29% at 10 min after occlusion in group 1, P less than 0.005) was observed in systole. Under propranolol (group 2), the results were similar to those of group 1. There were no significant changes in LVP, AoP, AoP, and NECS during occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)