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European Heart Journal 1993 14(5):712-716;
Copyright © 1993 by the European Society of Cardiology.
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© 1993 The Europen Society of Cardiology

Changes in canine ventricular fibrillation threshold induced by verapamil, flecainide and bretylium

A. QUESADA, J. SANCHIS, F. J. CHORRO, M. A. BURGUERA, A. ALBEROLA, L. SUCH and V. LOPEZ-MERINO

Department of Cardiology, Clinic University Hospital and Department of Physiology, University Medical School Valencia, Spain

Received 16 December 1992; .

Dr Francisco J. Chorro. Servicio de Cardiologia, Hospital Clinico Universitano. Av Blasco Ibañez, 17, 46010 Valencia. Spain

Abstract

The changes produced by verapamil, bretylium and flecainide in both ventricular fibrillation threshold (VFT) and ventricular repetitive response threshold (VRRT) were studied in 20 closed-chest dogs anaesthetized with pentobarbital.

Right ventricle endocardium thresholds were determined using bipolar electrode catheters. Increasing intensity stimulus trains (200ms, 4ms, 100 Hz, 1mA steps) were delivered 50 ms after QRS; VRRT and VFT were calculated before and after drug administration. Three study groups were considered according to the drug assayed: (1) verapamil 0.15 mg . kg–1 n=6; (2) flecainide 2.0 mg .kg–1 n=7, and (3) bretylium 10.0mg .kg–1 n=7. Flecainide significantly increased VRRT (4.8±1.4 vs 9.4±1.5 mA, P<0.05), but the latter failed to change in the other two groups. VFT remained unchanged with verapamil, increased slightly post-flecainide (10.3±4.6 vs 12.4±4.1, P<0.05 mA) and markedly post-bretylium (10.3±4.;6 vs 17.3 ± 7.5, P<0.05). VFT changes were significantly correlated (r=0.77, P<0.05) with the effective refractory period changes in the bretylium group.

Thus, of the three drugs tested, bretylium induced the greatest VFT increases without modifying VRRT, whereas flecainide affected both parameters. Only in the bretylium series were ERP changes significantly correlated to the corresponding VFT changes. This suggests that ventricular fibrillation threshold increase is not a non-specific property of antiarrhythmic drugs. Changes in ventricular repetitive response threshold may provide additional information

Key Words: Ventricular fibrillation • ventricular repetitive response • anti-arrhythmic drugs • anti-fibrillatory drugs • electrophysiology


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