Atrio-ventricular nodal re-entry tachycardia (AVNRT)

Atrio-ventricular nodal re-entry tachycardia (AVNRT) is caused by a re-entry circuit formed within the AV node causing atria and ventricles to be activated simultaneously. This can cause reflux of jugular venous blood and a sensation of pounding in the throat.

Fig 1: AVNRT
A: During sinus rhythm, condustion occurs through the AV node via a fast beta pathway
B: Typical AVNRT - When an APC fires the beta pathway has a slow refractory time and is temporarily not capable of ante grade conduction. Instead, conduction propagates through a slow alpha pathway. conduction then occurs normally to the ventricle; however, a retrograde impulse can travel through a re-entry loop.
C: Atypical AVNRT - When an APC fires, the beta pathway has fully depolarised and is capable of ante grade conduction. Conduction propagates normally to the ventricle; however a retrograde impulse can travel through the beta pathway and established a re-entry loop.