MODIFICATION OF ATRIOVENTRICULAR NODAL ELECTROPHYSIOLOGY BY SELECTIVERADIOFREQUENCY DELIVERY ON THE ANTERIOR OR POSTERIOR APPROACHES

An analysis was made in 14 isolated and perfused rabbit hearts of the electrophysiological effects of selective radiofrequency (RF) delivery in the anterior group I, n = 7) or posterior zone (group II, n = 7) o f the Koch triangle, with the aim of modifying atrioventricular nodal (AVN) conduction without suppressing 1:1 transmission. After opening t he right atrium, RF was delivered (0.5 W) with a 1-mm diameter unipola r electrode positioned in the selected zone until a prolongation of no less than 15% was obtained in the Wenckebach cycle length (WCL). Befo re and after (30 min) RF, anterograde and retrograde AVN refractorines s and conduction were evaluated, stimulating from the crista terminali s (CT), the interatrial septum (LAS), and from the RV epicardium. Afte r RF, the following percentage increments were observed in group I: AH (CT) = 36% +/- 9%, AH(IAS) = 38% +/- 11%, WCL(CT) = 28% +/- 8%, WCL(IA S) = 22% +/- 6%, functional refractory period (FRP) of the AVN(CT) = 1 3% +/- 11%, FRP-AVN(IAS) = 13% +/- 8%, retrograde WCL = 20% +/- 19%, a nd retrograde FRPVA = 13% +/- 16%. The increments observed in group II and the significances of the differences with respect to group I were : AH(CT) = 11% +/- 14% (P < 0.01), AH(IAS) = 19% +/- 32% (NS), WCL(CT) = 42% +/- 14% (P < 0.05), WCL(IAS) = 42% +/- 16% (P < 0.01), FRP-AVN( CT) = 28% +/- 28% (NS), FRP-AVN(IAS) = 21% +/- 19% (NS), retrograde WC L = 35% +/- 24% (NS), and retrograde FRP = 16% +/- 13% (NS). In both g roups, the AH interval variations were not correlated with those of th e rest of the parameters analyzed. Truncated nodal function curves sug gestive of a dual AV nodal pathway were obtained in three experiments, though in only one of them was this observed under basal conditions. In the other two experiments with dual AV nodal physiology only after RF lone from each group), AV nodal reentrant tachycardias were trigger ed with atrial extrastimulus at coupling intervals equal to or shorter than at those that cause a sudden lengthening of the AH interval. RF delivered in the anterior and posterior zones of the Koch triangle pro duced effects of different magnitude on the AH interval and Wenckebach cycle length. In the anterior zone the AH interval was prolonged to a greater extent, while in the posterior zone the effects were greater on the Wenckebach cycle length. No correlation existed between the var iations in AH interval and Wenckebach cycle length, regardless of wher e RF was delivered. The evaluation of anterograde AV nodal refractorin ess was similar when stimulating from the crista terminalis or from th e interatrial septum. By delivering RF, it was possible to induce dual AV nodal physiology and reentrant tachycardias.