Effect of alterations of arterial blood pressure and heart rate on segmental dyskinesis during acute myocardial ischemia and following coronary reperfusion.

The effect of alterations of blood pressure and heart rate on segmental dyskinesis induced by coronary artery ligation and the influence of such manipulations on the magnitude of recovery of the syskinetic segment during subsequent coronary artery reperfusion were evaluated in 77 open-chest dogs. Wall motion was recorded by ultrasound reflected directly from the ischemic myocardial segment. Acute ischemia produced characteristic regional abnormalities in wall motion: aneurysmal bulging occurred during isometric contraction and wall velocity was markedly reduced during ventricular ejection. During 69 minutes of ischemia, a control group of dogs underwent no interventions and showed no further changes in wall motion. Tachycardia induced by atrial pacing during ischemia had no significant effect. Arterial hypertension during ischemia caused a marked reduction in wall velocity when methoxamine was used: 14 plus or minus 2 (SE) mm/sec (ischemia alone) to 6 plus or minus 1 mm/sec (ischemia + drug). In contrast, norepinephrine improved wall velocity: 11 plus or minus 2 mm/sec (ischemia alone) to 25 plus or minus 4 mm/sec (ischemia + drug). Hypertension caused by infusion of phenylephrine gave intermediate results, as did hypotension induced by either nitroprusside or hemorrhage during the ischemic period. After 60 minutes the drugs were stopped, the coronary ligation released, and the ischemic myocardium reperfused. The relative order of improvement of wall velocity with reperfusion was 11 plus or minus 2 mm/sec (ischemia alone) to 24 plus or minus 3 mm/sec (reperfusion) in the group that received norepinephrine, 12 plus or minus 3 mm/sec to 20 plus or minus 3 mm/sec in the control group with no intervention durin ischemia, 13 plus or minus 2 mm/sec to 20 plus or minus 1 mm/sec in the nitroprusside group, 9 plus or minus 2 mm/sec in the phenylephrine group, and 14 plus or minus 2 mm/sec to 12 plus or minus 1 mm/sec in the methoxamine group. The aneurysmal bulging during isometric contraction also was reduced to a greater degree by reperfusion in the group that received norepinephrine during the ischemic period than it was in the groups undergoing other interventions during ischemia. We conclude that drug-induced elevations in arterial blood pressure can have different effects on the syskinetic motion of acutely ischemic myocardium and on the degree of recovery following reperfusion depending on the particular agent used.