AV Nodal Reentrant Tachycardia
Reentry involving tissue in/around the AV nodal region.
1. What might the surface ECG tell us?
Regular narrow-complex tachycardia is common; atrial activation may be simultaneous with or closely follow ventricular activation.
2. What might we see intracardially?
Concentric atrial activation is common. Atrial and ventricular timing can be very close in typical AVNRT.
Technologist mindset
Describe the sequence before naming the mechanism. Ask what is earliest, what follows, whether atrial and ventricular activation are linked, and whether the pattern changes with pacing.
3. Pacing clues
Programmed atrial/ventricular pacing and responses during tachycardia help test whether the atrium, ventricle, or an accessory pathway is required.
4. Mapping concept
The diagnostic goal is to establish the mechanism and distinguish AVNRT from AVRT and atrial tachycardia.
5. Ablation concept
When ablation is chosen, the procedural concept is modification of the slow-pathway region while protecting normal AV conduction.
Visual comparison: AVNRT vs AVRT
These diagrams are intentionally simplified. Their purpose is to teach relationships, not to replace full intracardiac interpretation.
Typical AVNRT — simplified concept
Orthodromic AVRT — simplified concept
VA timing: a useful clue, not a stand-alone diagnosis
Illustration only. Actual VA timing varies with mechanism, pathway location, conduction properties, measurement site and tachycardia.
Concentric vs eccentric atrial activation
| Pattern | What it describes | How to think about it |
|---|---|---|
| Concentric | Earliest retrograde atrial activation is relatively septal, with activation spreading outward. | Can occur in AVNRT and in AVRT using certain septal accessory pathways. It does not prove AVNRT. |
| Eccentric | Earliest atrial activation occurs away from the septal reference sites—for example in a lateral CS region. | Can raise suspicion for an accessory pathway or another nonconcentric atrial activation source, but requires full mechanistic evaluation. |
His-refractory PVC: the conceptual question
Why does timing matter?
A ventricular premature stimulus delivered when the His bundle is refractory can be used during selected tachycardias to ask whether ventricular activation through an accessory connection can influence the atrium or tachycardia circuit. A meaningful response may support accessory-pathway participation, but interpretation depends on exactly when and where the stimulus is delivered and how the tachycardia responds.
Ventricular overdrive pacing: what are we asking?
Overdrive pacing can perturb or entrain a tachycardia. The post-pacing response and measured intervals may provide clues about whether the ventricle participates in the circuit and how close the pacing site is to it. This is advanced EP reasoning and should be learned under qualified instruction rather than reduced to memorized cutoffs.
Quick knowledge check
What is the best learning sequence for AVNRT?
Professional reference
Open professional guidance →
Founder-authored educational summary. External expert review is not implied unless specifically stated.