Prevalence and Structured Approach to the Diagnoses of A on V Tachycardias

ABSTRACT Background “A on V” tachycardia (AoV‐T) is classically considered suggestive of atrioventricular nodal reentrant tachycardia (AVNRT); emerging evidence suggests that other mechanisms may present with this electrogram pattern. Objective To reassess the prevalence and electrophysiologic characteristics of nonconventional mechanisms underlying AoV‐T. Methods We retrospectively reviewed 1484 consecutive electrophysiologic studies for narrow‐QRS tachycardia with His–atrial interval ≤ 70 ms at 10 centers (2015–2024). Diagnoses were adjudicated using atrial overdrive pacing (AOP), ventricular overdrive pacing (VOP), and His‐synchronized premature ventricular contractions (PVCs). Results Mechanisms other than conventional AVNRT were identified in 24 patients (1.6%): atrial tachycardia (AT, n = 7), junctional tachycardia (JT, n = 6), orthodromic reciprocating tachycardia via an NV pathway (NV‐ORT, n = 6) or an NF pathway (NF‐ORT, n = 1), and AVNRT with a bystander NV pathway ( n = 4). AT arose from the crista terminalis ( n = 4) or para‐Hisian region ( n = 3) and was diagnosed by V‐A‐A‐V response following VOP and/or absence of VA linking during differential AOP; dual AV nodal physiology was frequently observed. JT was diagnosed with atrial extrastimulus and/or A‐H‐H‐A response after AOP. NV/NF‐ORT was diagnosed by combined findings, including tachycardia reset/termination with His‐refractory PVCs, short PPI – TCL, orthodromic His capture, and V‐V‐A response following VOP; QRS fusion favored NV‐ORT. AVNRT with a bystander NV pathway was distinguished from NV‐ORT by pacing responses consistent with AVNRT despite evidence of NV conduction. Conclusion Although AVNRT predominates in AoV‐T, a small subset of cases reflects AT, JT, NV/NF‐ORT, or AVNRT with a bystander NV pathway. Comprehensive pacing maneuvers are essential to avoid misclassification.