Electrophysiological abnormalities of the atrial muscle in patients with manifest Wolff-Parkinson-White syndrome associated with paroxysmal atrial fibrillation.

We investigated the electrophysiological properties of the atrial muscle in 33 patients with manifest Wolff-Parkinson-White syndrome. Group I consisted of 13 patients with paroxysmal atrial fibrillation and group II consisted of 20 patients without paroxysmal atrial fibrillation. The anterograde and retrograde effective refractory periods of the accessory pathway and the inducibility of atrioventricular reciprocating tachycardia were not significantly different between the two groups. Endocardial electrograms, obtained by right atrial catheter mapping, were recorded during sinus rhythm from 12 sites of the right atrium in 12 of the 13 group I patients and in all group II patients. An abnormal atrial electrogram was defined as 100 msec or longer in duration, and/or the occurrence of eight or more deflections. Ten (83%) of the 12 group I patients had abnormal atrial electrograms, while only two (10%) of the 20 group II patients had abnormal atrial electrograms, and the difference was significant (P less than 0.01). Thirty-six (26%) of the total 139 electrograms obtained from 12 group I patients and two (1%) of the total 199 electrograms obtained from 20 group II patients fulfilled the criteria for an abnormal atrial electrogram, and the difference was significant (P less than 0.01). The fragmented atrial activity zone, interatrial conduction delay zone, and repetitive atrial firing zone obtained by right atrial extrastimulation were significantly wider in group I than in group II, respectively. It was concluded that electrical abnormalities of the atrial muscle may play an important role in the occurrence of paroxysmal atrial fibrillation in patients with Wolff-Parkinson-White syndrome.