Case report: anterograde 2:1 and retrograde 3:2 Wenckebach block during atrioventricular nodal tachycardia: controversies of the upper and lower common pathways.

The exact nature of the reentry circuit for the atrioventricular nodal reentrant tachycardia (AVNRT) and particularly the concept and role of the upper and lower common pathways is not well defined. Although it is well accepted that the His-Purkinje system and the ventricles are not an essential part of the tachycardia circuit, controversy still exists as to whether the atria are essential components of the circuit. We describe a patient in whom the AVNRT perpetuated despite the spontaneous development of 2:1 anterograde and 3:2 retrograde block. To our knowledge, such a combination of electrophysiological phenomenon has not been previously reported. The electrophysiological basis of these observations and their clinical implications are discussed.