EFFECTS OF VERAPAMIL ON AUTOMATICITY AND CONDUCTION WITH PARTICULAR REFERENCE TO TACHYPHYLAXIS

  • 1 January 1979
    • journal article
    • research article
    • Vol. 9  (5) , 345-368
Abstract
Verapamil delivered via the sinus node artery exerted a dose-related, exclusively negative chronotropic action at all concentrations studied in dogs. Perfusion through the AV [atrioventricular] node artery during AV junctional rhythm also caused a dose-related negative chronotropic response but the concentration required to depress this pacemaker were 10 times higher than those required to depress sinus node automaticity. Verapamil administered into the AV node artery during sinus rhythm impaired AV conduction. His bundle electrograms showed that depressed A-V conduction was exclusively located at the A-H [atrio-nisian] level. In 5 of 10 dogs, verapamil (5-10 mg) delivered into the septal artery caused an abrupt onset of ventricular fibrillation without premonitory dysrhythmias. Verapamil (except at very high concentrations) did not alter the responsiveness of the sinus node and the AV junction to acetylcholine or norepinephrine, whether administered selectively into the sinus node artery or the AV node artery or released by neural stimulation. Serial injections of verapamil were associated with tachyphylaxis for the direct chronotropic and dromotropic properties of the drug.