Mechanisms for Atrial Fibrillation in Patients with Wolff-Parkinson-White Syndrome

Paroxysmal atrial fibrillation (PAF) frequently occurs in patients with Wolff-Parkinson-White (WPW) syndrome. To elucidate the mechanisms for PAF, we performed electrophysiologic studies (EPS) before and after ablation of accessory pathways (APs).We investigated 24 patients with WPW syndrome who had AV reciprocating tachycardia and prior PAF and had undergone successful ablation of APs. Patients in whom atrial fibrillation (AF) was induced by EPS at day 7 after ablation were considered the inducible AF group (n = 14), and patients in whom AF was not induced by EPS at day 7 after ablation were considered the noninducible AF group (n = 10). Fifteen patients with AV nodal reentrant tachycardia (AVNRT) but without PAF who underwent ablation of the slow AV nodal pathways served as the control group (AVNRT group). Maximal atrial conduction delay and conduction delay zone, which are indices of atrial vulnerability, were measured before and after ablation. Before ablation, maximal atrial conduction delay and conduction delay zone were significantly greater (P < 0.0001 and P < 0.0001, respectively) in the two WPW syndrome groups than in the AVNRT group, indicating increased atrial vulnerability in WPW syndrome with PAF. After ablation, these parameters did not change in the inducible AF group, whereas they were significantly (P < 0.0001) decreased in the noninducible AF group and were not different from those in the AVNRT group, indicating normalized atrial vulnerability in the noninducible AF group after ablation. The prospective study demonstrated that PAF recurred only in the inducible AF group during long-term follow-up (17+/-7 months).The findings of this study suggest that there are two mechanisms of PAF in patients with WPW syndrome: one mechanism is reversible and AP-dependent atrial vulnerability, and the other is intrinsic and AP-independent atrial vulnerability.