Atrial fibrillation and atrial vulnerability in the Wolff-Parkinson-White syndrome.

To explore the etiology of paroxysmal atrial fibrillation (AF) in the Wolff-Parkinson-White (WPW) syndrome, we examined the rates of AF episodes and performed electrophysiologic studies in 58 patients with WPW syndrome. They were classified into three patient groups depending on the property of antegrade conduction over accessory pathways: manifest WPW, intermittent WPW, and concealed WPW. Atrial vulnerability was defined as the inducibility of AF or repetitive atrial responses. The three groups were: 24 patients in manifest WPW, aged 42 +/- 15 yrs, 38% with AF; 12 patients in intermittent WPW, aged 40 +/- 15 yrs, 25% with AF; 22 patients in concealed WPW, aged 44 +/- 16 yrs, 9% with AF. There were no significant differences in the mean age between the groups. The incidences of atrial vulnerability detected in electrophysiologic studies in each group were 54%, 42%, and 27% respectively. The incidence of AF was well correlated with that of atrial vulnerability (p less than 0.01). The effective refractory periods (ERP) of the atrium and the retrograde ERP of the accessory pathway did not differ significantly between the three groups. Atrial conduction delay was more prominent in manifest WPW than in concealed WPW. The incidence of AF and atrial vulnerability was highest in the manifest WPW group, intermediate in the intermittent WPW group, and lowest in those patients with concealed WPW. The difference in incidence between the manifest WPW group and the concealed WPW group was significant (p less than 0.05). Therefore, the property of antegrade conduction over accessory pathways may be related to the genesis of AF in the WPW syndrome.