Effect of phentolamine on atrioventricular conduction in man assessed by recording His bundle potential.

The effect of phentolamine on atrioventricular conduction was studied in 6 patients using the technique of recording the His bundle potential. Right atrial pacing was used in order to keep the heart rate constant before and after administration of the drug. Increasing the heart rate by right atrial pacing resulted in a progressive increase in the PH interval, which represents atrial and atrioventricular conduction time, but had no effect on the HV interval, which represents intraventricular conduction. Ten mg phentolamine intravenously effectively shortened the PH interval and had no effect on the HV interval. In one patient this effect was blocked by the previous administration of 5 mg propranolol intravenously, suggesting that the mode of action of phentolamine may be through local release of catecholamines. Our results show that phentolamine improves atrioventricular nodal conduction and has no effect on intraventricular conduction.