AVNRT and AVRT Characteristics

Anatomic and Electrophysiologic Differences

The American Heart Association notes that AVNRT uses dual pathways within the AV node itself, while AVRT requires an accessory pathway connecting atrium to ventricle outside the normal conduction system 1, 2
The reentrant circuit in AVNRT 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 2
In typical AVNRT, anterograde conduction occurs down the slow pathway and retrograde conduction up the fast pathway, according to the American College of Cardiology 3, 2
The electrical pathway in AVRT requires an accessory pathway, the atrium, AV node, and ventricle, with the accessory pathway being an extranodal connection between atrial and ventricular myocardium across the AV groove 1, 2

Atrial activation in AVNRT occurs nearly simultaneously with ventricular activation, causing P waves to be buried within or at the end of the QRS complex, as noted by the Heart Rhythm Society 3, 4
In AVRT, retrograde P waves are usually clearly visible in the early part of the ST-T segment, separate from the QRS complex, according to the European Society of Cardiology 3, 5, 4

AVNRT is more common in middle-aged or older patients and has female predominance, while AVRT is more prevalent in adolescents and younger adults, with a mean symptom onset at 23 years versus 32 years for AVNRT, as reported by the American Heart Association 1
Patients with AVNRT more frequently describe "shirt flapping" or "neck pounding" sensations, which relate to pulsatile reversed flow when the right atrium contracts against a closed tricuspid valve, according to the American College of Cardiology 1

Atypical AVNRT variants can produce long RP intervals that mimic atrial tachycardia, and critical distinction is needed in AVRT with pre-excitation, where verapamil or diltiazem administration during pre-excited atrial fibrillation may cause hemodynamic collapse or ventricular fibrillation, as noted by the Heart Rhythm Society 3, 5, 4

In orthodromic AVRT, the reentrant impulse uses the accessory pathway in the retrograde direction from ventricle to atrium, and the AV node in the anterograde direction, with the accessory pathway being an extranodal connection between atrial and ventricular myocardium across the AV groove 6
This accessory pathway is anatomically separate from the AV node, distinguishing it fundamentally from AVNRT 6

AVNRT characteristically shows pseudo-R' waves in lead V1 and/or pseudo-S waves in inferior leads (II, III, aVF) due to simultaneous atrial and ventricular activation 7
In AVRT, the P wave morphology reflects the location of the accessory pathway, with deeply inverted P waves in inferior leads when the pathway is posteroseptal, and the American Heart Association recommends considering the P-wave morphology in the diagnosis of AVRT 6

AVNRT is more common in middle-aged or older patients with female predominance, with mean symptom onset at 32±18 years, and the American College of Cardiology recommends considering the age and gender of the patient in the diagnosis of AVNRT 8
AVRT is more prevalent in adolescents and younger adults, with mean symptom onset at 23±14 years, and the Heart Rhythm Society recommends considering the age and gender of the patient in the diagnosis of AVRT 8

Both AVNRT and orthodromic AVRT respond to vagal maneuvers and adenosine by blocking AV nodal conduction, with a strength of evidence level of I (high-quality evidence), and the American Heart Association recommends the use of vagal maneuvers and adenosine as a first-line treatment for AVNRT and AVRT 7
AVRT is treated with catheter ablation of the accessory pathway itself, with a success rate of 95-100%, and the Heart Rhythm Society recommends catheter ablation as a definitive treatment for AVRT 6