[Pseudo AV dissociation caused by interpolated junctional extrasystoles in the presence of a first-degree AV block].

This presentation reports an electrocardiogram showing first degree A-V block with a very prolonged P-R interval of 0.80 sec. On several occasions an arrhythmia occurred, characterized by what looked like an A-V junctional escape rhythm with A-V dissociation. This was suggested by a variable and, at first glance, haphazard relationship between QRS complexes and P waves. Analysis of the tracing suggested that the pattern was due to an interpolated A-V junctional extrasystole, followed by a sinus beat with an inordinately long P-R interval, whose duration was 1.18 sec. This very prolonged A-V conduction time made it difficult to recognize the relationship between P waves and QRS complexes, so that the pattern appeared as an A-V dissociation.