Decrease in repetitive extrasystole threshold during epinephrine infusion is enhanced in conscious dogs with...

Hypertension is associated with myocardial hypertrophy as well as increased adrenergic responsiveness, both of which can predispose to malignant ventricular arrhythmias. This study was designed to test the effects of subpressor doses of epinephrine (0.15 and 0.3 micrograms/kg/min x 30 min) on vulnerability to ventricular arrhythmia in normotensive and perinephritic hypertensive dogs. Two groups of 6 dogs each were chronically instrumented with aortic catheters to measure mean arterial pressure and bipolar pacing catheters in the apex of the right ventricle to measure repetitive extrasystole threshold, an index of vulnerability to ventricular fibrillation. In the normotensive dogs, the low dose of epinephrine (0.15 micrograms/kg/min IV) had no significant effects on mean arterial pressure, heart rate of repetitive extrasystole threshold. However, in the hypertensive dogs, the same dose caused a significant 39% increase in heart rate (p less than 0.05) and 41% decrease in repetitive extrasystole threshold (p less than 0.05). These findings suggest that electrophysiological vulnerability of the myocardium caused by epinephrine infusion is enhanced in the hypertensive animal.