Key Differences Between AVNRT and AVRT
AVNRT uses dual pathways confined within the AV node itself, while AVRT requires an accessory pathway connecting atrium to ventricle outside the normal conduction system—this fundamental anatomic distinction drives all their clinical and electrocardiographic differences. 1
Anatomic and Circuit Differences
Reentrant Circuit Location:
- AVNRT: The reentrant circuit is confined to the AV node and a small amount of perinodal atrial tissue, involving two functionally distinct pathways within the AV node termed "fast" and "slow" pathways 1, 2
- AVRT: Requires an accessory pathway (an extranodal connection between atrial and ventricular myocardium across the AV groove), plus the atrium, AV node, and ventricle to complete the circuit 1
Typical Circuit Direction:
- AVNRT: In typical (slow-fast) AVNRT, anterograde conduction occurs down the slow pathway and retrograde conduction up the fast pathway 1
- AVRT: In orthodromic AVRT (most common), anterograde conduction occurs down the AV node and retrograde conduction up the accessory pathway 1
ECG Characteristics During Tachycardia
P Wave Timing and Location:
- AVNRT: Atrial activation occurs nearly simultaneously with ventricular activation, causing P waves to be buried within or at the end of the QRS complex—this creates a "short RP" tachycardia with RP < 90 ms 3, 1
- AVRT: Retrograde P waves are usually clearly visible in the early part of the ST-T segment, separate from the QRS complex, occurring in 90-95% of episodes 1, 4
Specific ECG Findings:
- AVNRT: Pseudo-R' waves in lead V1 (slightly positive deflection at the end of QRS) and/or pseudo-S waves in inferior leads (II, III, aVF) due to simultaneous atrial and ventricular activation 3, 1, 5
- AVNRT: A notch in lead aVL appears in 51.3% of cases with 92.6% specificity 5
- AVRT: P wave morphology reflects the location of the accessory pathway, with deeply inverted P waves in inferior leads when the pathway is posteroseptal 1
VA Interval Variability at Tachycardia Onset:
- AVNRT: Shows significant VA interval variability at tachycardia induction, with median ∆VA of 40 ms (21-55 ms) and requiring 5 beats (4-7 beats) for stabilization 6
- AVRT: Minimal to no VA interval variability, with median ∆VA of 0 ms (0-5 ms) and stabilization within 1.5 beats (1-3 beats) 6
- A ∆VA < 10 ms accurately differentiates AVRT from atypical AVNRT with 100% sensitivity and specificity 6
Clinical Presentation Patterns
Age and Gender Distribution:
- AVNRT: More common in middle-aged or older patients with female predominance; mean symptom onset at 32±18 years 3, 1
- AVRT: More prevalent in adolescents and younger adults; mean symptom onset at 23±14 years 3, 1
Characteristic Symptoms:
- AVNRT: Patients more frequently describe "shirt flapping" or "neck pounding" sensations related to pulsatile reversed flow when the right atrium contracts against a closed tricuspid valve (cannon a-waves) 3, 1, 2
- AVRT: Palpitations without the specific neck pounding sensation characteristic of AVNRT 3
Treatment Response and Implications
Acute Management:
- Both respond similarly to vagal maneuvers and adenosine by blocking AV nodal conduction, as both require the AV node as part of their reentrant circuit 3, 1
- Critical caveat: In AVRT with pre-excitation (manifest accessory pathway), verapamil or diltiazem administration during pre-excited atrial fibrillation may cause hemodynamic collapse or ventricular fibrillation 3, 1
Definitive Treatment:
- AVNRT: Catheter ablation targets the slow pathway within the AV node, with high success rates and low complication risk 1, 2
- AVRT: Catheter ablation targets the accessory pathway itself, with success rates of 95-100% 1
Spontaneous Termination Patterns:
- Both AVNRT and AVRT terminate spontaneously in similar patterns: 60% with antegrade block (preceded by AH interval prolongation, Mobitz type-I) and 40% with retrograde block (sudden, Mobitz type-II) 7
Electrophysiologic Study Distinctions
Entrainment Response: