Clinical evaluation of the enhancement of vagal tone in acute myocardial infarction by edrophonium hydrochloride: Effects on ventricular arrhythmias, His bundle electrography, and left ventricular function

Enhanced electrical stability of acutely ischemic myocardium with vagal stimulation and acetylcholinesterase inhibition has been demonstrated experimentally. To extend these findings clinically, within 24 hours of acute myocardial infarction, 11 patients underwent continuous 10 hour Holter monitoring: 2.5 hour control before and after 5 hour constant edrophonium infusion (0.25 to 2.00 mg./minute). Continuous infusion of the agent lowered heart rate 92 to 78 b.p.m. (p<0.01). Although mean total ventricular extrasystoles (PVC's) per 5 hours per patient (131) and PVC's per 1,000 beats (4.7) were unchanged (p>0.05), potentially lethal tachyarrhythmias (malignant PVC's: multifocal, R on T, paired, >5 per minute or ventricular tachycardia) were terminated in six of 10 patients by edrophonium. However, serious ventricular arrhythmias continued in three patients and appeared in four despite the agent. Ventricular fibrillation did not occur during the 10 hour period of study. In addition, the patients were evaluated hemodynamically and by His bundle electrograms before and after a 10 mg. bolus of edrophonium prior to the 10 hour constant infusion: heart rate declined (88 to 72 b.p.m., p<0.01), while mean arterial pressure (98 mm. Hg), left ventricular filling pressure (14 mm. Hg), cardiac index (2.4 L. per minute per square meter), and stroke work index (36 Gm.m./M.²) were unchanged (p>0.05). The edrophonium bolus prolonged the A-H interval (117 to 135 msec., p<0.01) while the H-Q interval was unaltered (48 msec.; p>0.05). It is concluded that increased vagal tone with edrophonium did not reduce the over-all presence of premature ventricular contractions in the entire study group; however, the malignant nature of PVC's and ventricular tachycardia appeared to be lessened by the parasympathomimetic agent in certain patients. In addition, no adverse hemodynamic or intraventricular conduction effects were produced by edrophonium administration.