Radiofrequency versus pharmacologic modification of the atrioventricular node

Abstract

Although transcatheter radiofrequency modification of the atrioventricular (AV) node has been proposed as curative treatment in AV nodal reentry tachycardias, its role for the control of the ventricular rate in atrial tachyarrhythmias remains unclear. The aim of this study was to analyze the acute effect of radiofrequency current on AV nodal conduction and refractoriness, and to compare it with the effects of two antiarrhythmic drugs such as amiodarone (class III) and flecainide (class I). Twenty-one dogs were studied: (1) radiofrequency group (5 W for less than 45 seconds; 2 to 12 discharges: seven dogs); (2) amiodarone group (5 mg/kg intravenously; seven dogs); and (3) flecainide group (2 mg/kg intravenously; seven dogs). The following parameters were measured under basal conditions and after each procedure: AH interval, AV nodal functional refractory period, Wenckebach cycle length, minimum R-R interval during atrial fibrillation, and fitting of AV nodal function curve to a hyperbolic equation using its linear transformation. The AV nodal effective refractory period could not be calculated in any dog in the basal study because it was shorter than the atrial functional refractory period. After radiofrequency, the percentage increment was greater for the AH interval than for the AV nodal functional refractory period (60 ± 28% versus 29 ± 16%, p ≤ 0.05); the percentage increment in the AH interval did not correlate with that of any other interval, whereas the percentage increment of the AV nodal functional refractory period correlated with that of the Wenckebach cycle length ( r = 0.83, p ≤ 0.05) and minimum R-R interval during atrial fibrillation ( r = 0.78, p ≤ 0.05). Neither after amiodarone (62 ± 16% versus 50 ± 21%, p = NS) nor after flecainide (18 ± 7% versus 12 ± 6%, p = NS) were there significant differences between the percentage incremento in the AH interval and AV nodal functional refractory period; furthermore, unlike radiofrequency, the percentage increment in the AH interval correlated with that of the AV nodal functional refractory period after amiodarone ( r = 0.87, p ≤ 0.01) and flecainide ( r = 0.86, p ≤ 0.01). The AV nodal function curve was displaced upwards and to the right with each procedure; the ordinate axis intercept of the straight line of the hyperbolic equation significantly decreased only with amiodarone. It was concluded that: (1) Radiofrequency current, unlike antiarrhythmic drugs, induces a dissociation between conduction and refractoriness, with a predominant modification of the former. (2) The prolongation of the parameters valuable in controlling ventricular rate in atrial tachyarrhythmias (Wenckeback cycle length and minimum R-R interval during atrial fibrillation) depends on the modification of AV nodal refractoriness and not on the increase in the AH interval. (3) The prolongation of the AH interval can be a misleading end point during the ablation procedures.