Atrioventricular Reentrant Tachycardia
Macroreentry using the AV node/His-Purkinje system and an accessory atrioventricular pathway as limbs of the circuit.
1. What might the surface ECG tell us?
Orthodromic AVRT is commonly narrow-complex; preexcitation may be present in sinus rhythm when the pathway conducts antegradely.
2. What might we see intracardially?
Atrial activation sequence can provide clues to pathway location, but sequence alone does not prove AVRT.
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
Ventricular pacing and tachycardia responses can test whether the ventricle and accessory pathway participate in the circuit.
4. Mapping concept
Mapping seeks the site of accessory-pathway conduction by integrating activation timing, anatomy, and electrogram characteristics.
5. Ablation concept
Ablation targets accessory-pathway conduction when clinically appropriate.
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 AVRT?
Professional reference
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Founder-authored educational summary. External expert review is not implied unless specifically stated.