Paroxysmal atrial fibrillation initiated by late coupled atrial extrasystoles.

A Holter recording was taken from a 62-year-old man, in whom paroxysmal atrial fibrillation was often initiated by late coupled extrasystoles rather than by close coupled ones. Coupling intervals of the extrasystoles to the preceding sinus P waves were considerably variable. When the coupling interval of an extrasystole was shorter than a critical period of 0.47 s, the extrasystole failed to be followed by another ectopic atrial deflection. On the other hand, when the coupling of an extrasystole was longer than 0.47 s, the extrasystole was followed by another atrial deflection, or it was followed by a short run of atrial tachycardia, which initiated paroxysmal atrial fibrillation. To our knowledge, such atrial fibrillation initiated by late coupled atrial extrasystoles has never been reported previously. Longitudinal dissociation in the re-entrant pathway of the extrasystoles is suggested as a possible mechanism for such initiation of paroxysmal atrial fibrillation.