Dual AV nodal pathways and conduction during atrial fibrillation

AV node modification reduces ventricular rate during atrial fibrillation (AF). We induced AF in patients with dual AV nodal pathways before and after radiofrequency ablation (RFA) of AV nodal reentry tachycardia (AVNRT) and examined the role of the two pathways in the transmission of impulses during AF.

AF was induced in 30 patients before and after slow pathway ablation. Before RFA mean (AF CLmean) and shortest (AF CLshort) ventricular cycle lengths correlated significantly to ERPf, ERPs, and antegrade Wenckebach block (r = 0.53-0.67). Ablation eliminated slow pathway conduction completely in 10 patients (group A), whereas in 20 patients some slow pathway conduction was still present (group B). After RFA there was a 10% increase in AF CLmean (20%, p < 0.05 in A and 5%, p = NS in B) and 7% in AF CLshort (11%, p = NS in A and 6%, p = NS in B). During isoproterenol infusion after RFA AF CLmean increased 8% (p < 0.05) (14% in A and 6% in B; p < 0.05 in both groups). The effects of RFA were mainly confined to patients with ERPs less than the median value (13% vs 3% in those above median, respectively; p < 0.05).

The refractory periods of the AV nodal pathways are the main determinants of ventricular rate during induced AF. Slow pathway ablation reduces ventricular rate during AF. This effect was greatest when slow pathway conduction was completely eliminated. A short ERPs predicted a greater reduction in ventricular rate.