Effect of verapamil directly administered into A-V node artery on A-V junctional automaticity and A-V conduction in...

We investigated the direct effects verapamil, which was infused into the A-V node artery at two doses of 0.01 and 0.1 microgram/kg/min on the A-V conduction and the A-V junctional automaticity in the dog with experimentally induced A-V junctional rhythm. Verapamil significantly prolonged the A-H interval, but not the H-V interval, in the His bundle electrogram during atrial pacing at a rate of 100 beats/min. Effective and functional refractory periods of the A-V node also were prolonged significantly by verapamil. On the other hand, verapamil showed less propensity to decrease the spontaneous A-V junctional rate and to prolong the A-V junctional recovery time after atrial overdrive at a rate of 100 beats/min for 60 s. These results indicate that suppressive effects of verapamil on the A-V junctional automaticity are much weaker when compared with that on the A-V conduction.