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

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: = 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.