Electrophysiological effects of intravenous prostacyclin in man

The electrophysiological effects of prostacyclin (PGI₂) werestudied in 10 normal patients. Programmed stimulation was performedbefore and after infusion of 2.5, 5, 10ng kg^–1 min^–1of PGI₂. Then, 0.2 mg kg^–1 of propranolol was added tothe higher dose of PGI₂.We observed a net decrease of the systolicand diastolic arterial blood pressure beginning with the lowestdose. There was no effect on sinus node recovery time, atrial,His-Purkinje and ventricular effective refractory periods, AHand HV intervals. Atrioventricular (AV) nodal effective andfunctional refractory periods could be measured in 5 patientsand were decreased in all cases. Sinus cycle length and anterogradeand retrograde Wenckebach cycle lengths were significantly decreasedby PGI₂ in a dose dependant manner. The injection of propranololincreased all these values but did not suppress entirely theeffects of PGI₂.In conclusion, the electrophysiological effectsof PGI₂ were marked decreases of sinus cycle length and AV nodalrefractoriness which may be partly related to enhanced sympatheticactivity.