Simultaneous dual AV node antegrade conduction (2 for 1) and lower common pathway (2–1) block illustrate AVNRT physiology

We report a rare case of spontaneous initiation of Atrioventricular nodal reentry tachycardia (AVNRT) via 2 for 1 phenomenon, into a 2:1 AV block due to lower common pathway block and finally transition to 1:1 tachycardia. The premature atrial p wave traverses down both the fast and slow pathway simultaneously during 2 for 1 initiation and is met with subsequent typical AVNRT with 2:1 block. Infranodal location of the block is confirmed on electrophysiologic testing and is also cured by intervention. This rare electrographic presentation is not only pathognomonic for AVNRT with lower common pathway block but also illustrates its dual conduction physiology.