Atrioventricular nodal reentrant tachycardia is the most common form of paroxysmal supraventricular tachycardia, or PSVT, in adults. AVNRT occurs when a reentrant circuit is present within the AV node itself. In this situation, there are two separate conduction pathways within the AV node instead of just one (present in about 5% of the general population).
This is sometimes termed “dual AV nodal physiology.” One pathway is slower and has a short refractory period, while the other is faster and has a long refractory period. Normal conduction occurs through the faster pathway with the long refractory period.
If a premature atrial contraction, or PAC, or less commonly a premature ventricular contraction, or PVC, occurs at the right time, the normal conduction pathway will still be refractory; thus, the action potential will conduct through the fast AV nodal pathway with the shorter refractory period instead. After this action potential reaches the ventricles or atrium, it will conduct back through the normal AV nodal conduction pathway, as it will no longer be refractory and a reentrant circuit will be created.
Initiation of AVNRT with a PVC
Findings on ECG include the following:
Narrow complex tachycardia
A P wave that occurs after the QRS complex (a short RP interval)
Tachycardia that quickly terminates with AV blocking maneuvers (carotid massage or adenosine)
1. Chou's Electrocardiography in Clinical Practice: Adult and Pediatric, Sixth Edition, Saunders, Philadelphia, 2008.
2. Surawicz B, et al. AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram. Circulation. 2009; doi:10.1161/CIRCULATIONAHA.108.191095.