Paradoxical ventriculophasic sinus arrhythmia during 2:1 atrioventricular block.

Ventriculophasic sinus arrhythmia is a particular phenomenon commonly observed in patients with complete atrioventricular (AV) block. Typically, the PP intervals which contain a QRS complex are shorter than the PP intervals which do not contain it. This phenomenon is present in more than 40% of cases with complete AV block and less common in the setting of second-degree AV block. We present a case with paradoxical ventriculophasic sinus arrhythmia during 2:1 AV block, in which the PP intervals containing a QRS complex are longer than the PP intervals without an intervening QRS complex. The possible mechanisms regarding this unusual phenomenon are also discussed.