Electrophysiological effects of intravenous prostacyclin in man

The electrophysiological effects of prostacyclin (PGI2) were studied in 10 normal patients. Programmed stimulation was performed before and after infusion of 2.5, 5, 10 ng kg-1 min-1 of PGI2. Then, 0.2 mg kg-1 of propranolol was added to the higher dose of PGI2. We observed a net decrease of the systolic and diastolic arterial blood pressure beginning with the lowest dose. There was no effect on sinus node recovery time, atrial, His-Purkinje and ventricular effective refractory periods, AH and HV intervals. Atrioventricular (AV) nodal effective and functional refractory periods could be measured in 5 patients and were decreased in all cases. Sinus cycle length and anterograde and retrograde Wenckebach cycle lengths were significantly decreased by PGI2 in a dose dependent manner. The injection of propranolol increased all these values but did not suppress entirely the effects of PGI2. In conclusion, the electrophysiological effects of PGI2 were marked decreases of sinus cycle length and AV nodal refractoriness which may be partly related to enhanced sympathetic activity.