EFFECTS OF DILTIAZEM THERAPEUTIC PLASMA-LEVELS ON CARDIAC CONDUCTION AND REFRACTORINESS

  • 1 January 1981
    • journal article
    • research article
    • Vol. 252  (2) , 272-283
Abstract
The effects of diltiazem, a new slow channel inhibitor, on the cardiac conduction and refractoriness were studied using His bundle recordings and the extrastimulus method. To determine the role played by possible changes in vagal tone, diltiazem (0.15 mg kg-1, followed immediately by a 30 min infusion of 0.01 mg kg-1 min-1) was administered i.v. to 6 atropinized dogs, anesthetized with chloralose (100 mg kg-1) (atropine group) and to 6 others which were given chloralose (80 mg kg-1) and dextromoramide (0.1 mg kg-1) to ensure the persistance of vagal tone (vagal tone group). In the atropine group, atrioventricular (AV) nodal conduction time increased by 137% and AV node effective refractory period by 55%. Heart rate was slowed down by 15% and arterial pressure fell slightly. In the vagal tone group, the only significant changes were a 26% increase in AV nodal conduction time and a slight fall in arterial pressure. Inhibition of the slow channel accounts for the effects of diltiazem within the atropine group. A reflex decrease in vagal tone is probably responsible for the somewhat different results observed in the vagal tone group. Diltiazem resembles verapamil and should share its antiarrhythmic properties.