Mode of onset of atrial fibrillation in the Wolff-Parkinson-White syndrome: how important is the accessory pathway?

The mode of onset of 103 episodes of atrial fibrillation lasting greater than or equal to 30 s was studied in 79 patients with the Wolff-Parkinson-White syndrome during electrophysiologic study. No patient had organic heart disease, and 31 had clinical atrial fibrillation before study. These 79 patients were then compared with a control group of 53 patients with Wolff-Parkinson-White syndrome in whom atrial fibrillation could not be induced. Ninety-five of the 103 episodes were technically suitable for analysis. Atrial fibrillation invariably began with rapid atrial tachycardia that became progressively disorganized within 10 to 20 cycles. It was initiated during right atrial stimulation (n = 52), right ventricular stimulation (n = 8), reciprocating tachycardia (n = 33) and spontaneously (n = 2). Most episodes started at a high right atrial site regardless of accessory pathway location, with only 19% of episodes starting at the electrode closest to the accessory pathway. During reciprocating tachycardia (n = 33), either atrial (n = 8) or ventricular (n = 5) extrastimuli initiated atrial fibrillation. Atrial fibrillation started at the accessory pathway site in 6 of 20 episodes occurring spontaneously during reciprocating tachycardia. Patients with atrial fibrillation had a longer PA interval (54 +/- 14 versus 42 +/- 12 ms, p less than 0.0001), shorter atrial functional refractory period (226 +/- 38 versus 240 +/- 30 ms, p = 0.049) and shorter anterograde effective refractory period of the accessory pathway (279 +/- 26 versus 304 +/- 75 ms, p = 0.03). Clinical reciprocating tachycardia was documented with equal frequency in both the atrial fibrillation and control groups (59.5% versus 52.9%, p = 0.58).(ABSTRACT TRUNCATED AT 250 WORDS)