His bundle electrogram recordings showed that right atrial pacing and digitalis prolonged the P-H interval, whereas isoproterenol and atropine shortened it, without affecting the H-Q interval.
How do right atrial pacing, digitalis, isoproterenol, and atropine affect the P-H and H-Q intervals during His bundle recordings in humans?
This physiological study demonstrates that interventions like pacing, digitalis, isoproterenol, and atropine primarily affect AV nodal conduction (P-H interval) rather than His-Purkinje conduction (H-Q interval).
The technique of recording electrograms of the His bundle, using a tripolar electrode catheter positioned across the tricuspid valve, was applied in a physiological study of atrioventricular conduction in man. Increasing the heart rate to 160 beats/min by right atrial pacing produced progressive prolongation of the P-H interval while the H-Q interval remained constant. At any given paced heart rate, digitalis caused a prolongation of the P-H interval. Isoproterenol and atropine markedly shortened the P-H interval at any given heart rate. Neither drug had any significant effect on the H-Q interval. Coupled premature atrial stimulation produced prolongation of the P-H interval alone when the resultant ventricular depolarization was normal, and prolongation of both the P-H and H-Q intervals when the resultant ventricular depolarization was aberrant.
Damato et al. (1969) studied Atrioventricular conduction. Right atrial pacing and pharmacological agents (digitalis, isoproterenol, atropine) was evaluated on P-H and H-Q intervals. His bundle electrogram recordings showed that right atrial pacing and digitalis prolonged the P-H interval, whereas isoproterenol and atropine shortened it, without affecting the H-Q interval.