AVRT and AVNRT Definitions
AVRT stands for Atrioventricular Reentrant Tachycardia, and AVNRT stands for Atrioventricular Nodal Reentrant Tachycardia. 1
Key Distinctions Between These Arrhythmias
AVNRT (Atrioventricular Nodal Reentrant Tachycardia)
AVNRT is a reentrant tachycardia involving two functionally distinct pathways within the AV node itself, generally referred to as "fast" and "slow" pathways, with the reentrant circuit confined to the AV node and a small amount of perinodal atrial tissue. 1, 2
In typical AVNRT (the most common form), anterograde conduction occurs down the slow pathway and retrograde conduction up the fast pathway, also called "slow-fast AVNRT." 1, 2
Atypical AVNRT variants exist where the fast pathway serves as the anterograde limb and a slow pathway serves as the retrograde limb ("fast-slow"), or where two slow pathways are involved ("slow-slow AVNRT"). 1
AVRT (Atrioventricular Reentrant Tachycardia)
AVRT is a reentrant tachycardia whose electrical pathway requires an accessory pathway (an extranodal connection), the atrium, the atrioventricular node (or second accessory pathway), and the ventricle. 1
Orthodromic AVRT uses the accessory pathway in the retrograde direction (ventricle to atrium) and the AV node anterogradely, producing a generally narrow QRS complex. 1
Antidromic AVRT uses the accessory pathway anterogradely (atrium to ventricle) and the AV node retrogradely, producing a wide, maximally pre-excited QRS complex. 1
Clinical Recognition Features
ECG Characteristics
In AVNRT, atrial activation occurs nearly simultaneously with ventricular activation, causing P waves to be buried within or at the end of the QRS complex (appearing as pseudo r'-waves in V1 or pseudo S-waves in inferior leads). 1, 2
In AVRT, retrograde P waves are usually clearly visible in the early part of the ST-T segment, separate from the QRS complex. 2
Age and Demographics
AVNRT is more common in middle-aged or older patients (mean symptom onset 32 years) and has female predominance, while AVRT is more prevalent in adolescents and younger adults (mean symptom onset 23 years). 1, 2, 3
AVNRT is the most common form of paroxysmal supraventricular tachycardia overall, particularly in older populations. 3, 4
Critical Treatment Pitfall
In AVRT with pre-excitation (Wolff-Parkinson-White syndrome), administration of verapamil or diltiazem during pre-excited atrial fibrillation may cause hemodynamic collapse or ventricular fibrillation by enhancing conduction down the accessory pathway and accelerating the ventricular rate. 1, 2, 5