Try to interpret the above Intracardiac tracing. Most will notice the very short VA time prior to VODP, which already argues strongly against AVRT. Just before termination, there is full RV capture at 300ms, with the atria continuing independently at 335ms. This VA dissociation would be highly unusual in AVRT, as AVRT requires both atrial and ventricular participation to sustain the circuit. The tachycardia would not persist this long under these conditions if AVRT were the mechanism. It would either terminate immediately or the atria would be accelerated to the pacing cycle length prior to termination.
If the tachycardia terminates without atrial acceleration, think AVNRT. If the atria never depolarise to the pacing cycle length, atrial tachycardia is not possible.
So the most likely diagnosis in above tracing is AVNRT
Systematic Evaluation of EP Maneuvers to Diagnose AVNRT During Electrophysiology Study (EPS)
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Introduction
Atrioventricular Nodal Reentrant Tachycardia (AVNRT) is the most common form of paroxysmal supraventricular tachycardia encountered in electrophysiology laboratories. It results from reentry within the AV node utilizing dual AV nodal pathways — a slow pathway and a fast pathway.
During an electrophysiology study (EPS), several pacing maneuvers are used systematically to confirm that the tachycardia mechanism is AVNRT and to differentiate it from other supraventricular tachycardias such as AVRT or atrial tachycardia.
A structured stepwise approach greatly improves diagnostic accuracy.
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Baseline Electrophysiology Assessment
Before tachycardia induction, baseline conduction parameters are evaluated.
Important measurements include:
AH Interval
Represents conduction time from atrium to His bundle through the AV node.
Normal range: 50–120 ms.
HV Interval
Represents conduction from His bundle to ventricular myocardium.
Normal range: 35–55 ms.
Evidence of dual AV nodal physiology should be assessed using atrial extrastimulus testing.
Dual AV Nodal Physiology
Defined by an AH jump.
Criteria: Increase in AH interval ≥50 ms when the atrial coupling interval decreases by 10 ms.
This indicates the presence of both slow and fast AV nodal pathways, a prerequisite for AVNRT.
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Induction of Tachycardia
Tachycardia is typically induced using:
Atrial burst pacing
Atrial extrastimulus pacing
Isoproterenol infusion (if tachycardia is not inducible)
Once sustained narrow complex tachycardia is induced, EP maneuvers are used to confirm the mechanism.
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Key EP Maneuvers for Diagnosing AVNRT
1. Ventricular Overdrive Pacing (VOP)
Ventricular pacing is performed during tachycardia at a rate slightly faster than the tachycardia cycle length.
Key observations:
Post Pacing Response (PPR)
In AVNRT the classic response is:
V-A-V response
Explanation: The first signal after pacing is ventricular, followed by atrial activation through the slow pathway and then continuation of tachycardia.
This VAV pattern strongly supports AVNRT or AVRT and excludes atrial tachycardia.
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2. Post Pacing Interval (PPI – TCL)
Post Pacing Interval (PPI) is the interval from the last paced ventricular beat to the next atrial electrogram during tachycardia.
TCL = Tachycardia Cycle Length.
Calculation: PPI – TCL
Interpretation:
PPI – TCL >115 ms strongly favors AVNRT
PPI – TCL <115 ms suggests AVRT
Reason: In AVNRT the ventricle is not part of the reentrant circuit, therefore pacing must travel retrogradely through the His-Purkinje system and AV node before reaching the circuit, increasing the interval.
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3. SA – VA Difference
SA interval: Stimulus to atrial electrogram during ventricular pacing.
VA interval: Ventricular electrogram to atrial electrogram during tachycardia.
Calculation: SA – VA difference.
Interpretation:
SA – VA >85 ms strongly favors AVNRT
SA – VA <85 ms favors AVRT
This maneuver helps determine whether the ventricle is part of the tachycardia circuit.
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4. His Refractory PVC
A premature ventricular contraction is delivered when the His bundle is refractory.
Observation:
If the PVC advances the next atrial signal → suggests AVRT (accessory pathway present)
If the PVC does not affect atrial timing → favors AVNRT
Explanation: In AVNRT the ventricle is outside the circuit and therefore cannot perturb atrial activation.
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5. VA Interval During Tachycardia
VA interval is measured from ventricular electrogram to atrial electrogram.
Typical AVNRT finding:
Short VA interval <70 ms
This occurs because retrograde conduction to the atrium occurs through the fast pathway located near the AV node.
In contrast:
AVRT usually has longer VA intervals.
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6. Atrial Overdrive Pacing
Rapid atrial pacing during tachycardia can provide additional clues.
Findings favoring AVNRT:
Tachycardia termination without atrial activation
AH prolongation before tachycardia termination
These findings support involvement of AV nodal pathways in the circuit.
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7. His Bundle Timing
During AVNRT the His signal is activated before each ventricular electrogram.
Sequence typically seen:
A → H → V
His activation precedes ventricular activation because the AV node is the central part of the circuit.
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Typical Electrophysiologic Characteristics of AVNRT
Dual AV nodal physiology (AH jump)
Short VA interval (<70 ms)
V-A-V response after ventricular overdrive pacing
PPI – TCL >115 ms
SA – VA difference >85 ms
His refractory PVC does not advance atrium
These findings collectively confirm AVNRT.
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Differentiation from AVRT and Atrial Tachycardia
Feature | AVNRT | AVRT | Atrial Tachycardia
VA interval | Short (<70 ms) | Long | Variable
PPI – TCL | >115 ms | <115 ms | Variable
SA – VA | >85 ms | <85 ms | Variable
His refractory PVC | No effect | Advances atrium | No effect
VOP response | V-A-V | V-A-V | A-V
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Clinical Importance
Accurate identification of AVNRT during EPS is essential because the treatment strategy differs from other tachycardias.
In AVNRT, radiofrequency ablation targets the slow pathway in the posteroseptal right atrium near the coronary sinus ostium.
Slow pathway modification has a success rate exceeding 95% with a very low complication rate.
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Conclusion
A systematic evaluation using EP pacing maneuvers allows precise identification of AVNRT during electrophysiology studies. No single maneuver is diagnostic on its own, but combining multiple findings such as V-A-V response, prolonged PPI-TCL, large SA-VA difference, and lack of atrial advancement with His refractory PVC strongly confirms the diagnosis.
Understanding these electrophysiologic principles is essential for electrophysiologists to differentiate AVNRT from AVRT and atrial tachycardia and to guide effective catheter ablation therapy.
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