EFFECTS OF HYPOCALCEMIA ON ATRIOVENTRICULAR-CONDUCTION COMPARED WITH THOSE OF AGENTS WHICH INHIBIT THE SLOW CHANNEL

  • 1 January 1980
    • journal article
    • research article
    • Vol. 11  (4) , 379-389
Abstract
The effects of experimental hypocalcemia were studied on 13 anesthetized and atropinized dogs, measuring endocavitary His bundle recordings, global effective refractory period (ERP) (determination by the extrastimulus method) and sinus rate. These data, including arterial pressure, were observed during a 40 min, i.v. infusion of Na EDTA, 3 mg/kg per min. Serum ionized Ca decreased from 45,7 mg/l (control) to 28,1 mg/l. A moderate, though highly significant, decrease in the intraatrial conduction time (SA interval of His bundle recordings) was observed. The AV node conduction time (AH) significantly increased. No significant change occurred in the His-Purkinje system conduction time (HV). A significant increase in the global ERP, primarily involving the atrial contractile tissue ERP and the atrioventricular node ERP was seen. A slowing of the sinus node discharge rate slowed and arterial pressure fell significantly. These results are similar to those obtained by the same method with agents which inhibit the slow channel such as nifedipine and verapamil. An inhibition of inward Ca current most probably accounts for them, except for the increase in atrial ERP, which suggests that hypocalcemia interferes with ion movements other than Ca.