A real ECG case of antidromic AVRT via a Mahaim (atriofascicular) pathway — checked against the EP literature, with the actual named diagnostic criteria the post's pearls are built on.
Mahaim (atriofascicular) pathways are a genuinely distinct entity from typical WPW accessory pathways, and the post's circuit description is textbook-accurate.
Atriofascicular Mahaim fibers connect the right atrium to the distal right bundle branch/RV myocardium, are classically decrementally conducting (like the AV node) and antegrade-only (unlike typical WPW pathways, which usually conduct in both directions). During antidromic AVRT, the Mahaim pathway is necessarily the antegrade limb (RA→pathway→RV) with the AV node/His-Purkinje system completing the circuit retrogradely — exactly as the post describes. Because ventricular activation starts in the right ventricle and propagates toward the left, the resulting QRS mimics a left bundle branch block pattern.
Negative V1–V4, late R-wave transition, LBBB-type wide QRS — all textbook-accurate for this mechanism.
Right-to-left ventricular activation via an atriofascicular pathway classically produces: an LBBB-type wide QRS, an rS (negative-dominant) pattern in the early precordial leads as the initial activation vector moves away from V1–V4, and a late R-wave transition typically after V4 (sometimes V5–V6) as activation reaches the posterior/left ventricle late. This matches published descriptions closely, including the specific "late transition after lead V4" language used in differential-diagnosis literature on LBBB-pattern wide-complex tachycardias.
Worth having on hand if you want a citable, validated checklist rather than gestalt pattern recognition.
Six ECG features, together showing high efficacy for distinguishing antidromic Mahaim tachycardia from other wide-complex tachycardias, including VT: (1) QRS axis between 0° and −75° (left axis), (2) QRS duration ≤0.15 sec, (3) R wave in limb lead I, (4) rS pattern in precordial lead V1, (5) precordial transition to a predominantly positive QRS after V4, (6) tachycardia cycle length 220–450 ms. A follow-up validation study found these criteria have 87.5% sensitivity and 82.5% negative predictive value specifically within atriofascicular pathways — the main source of false positives being aberrantly conducted tachycardia with ventriculoatrial conduction over a separate accessory AV pathway.
This maps directly onto the post's own summary: the "negative QRS polarity in inferior leads" clue corresponds to the Bardy criteria's left-axis-deviation requirement (0° to −75° produces negative deflection in the inferior leads II, III, aVF), and the "late R-wave transition in V5–V6" matches criterion 5 almost exactly.
VT always belongs in the differential for any wide-complex tachycardia, and the post says so correctly.
The post's caution — that a regular LBBB-pattern WCT should raise suspicion for antidromic Mahaim-mediated AVRT but VT must always remain on the differential — is the correct clinical stance. Even the validated Bardy criteria, at 87.5% sensitivity, aren't perfect; the published false-positive/false-negative literature specifically flags aberrantly conducted SVT with an accessory-pathway VA connection as the main confounder, underscoring why pattern criteria alone shouldn't override clinical judgment or, where needed, formal EP study.
This case-based teaching post holds up completely against the EP literature — the circuit description, the mechanism behind the ECG pattern, and the differential diagnosis caveat are all accurate. The one thing worth bookmarking alongside it: the Bardy criteria, the actual named, validated 6-point ECG checklist (axis, QRS duration, lead I, V1 morphology, precordial transition point, cycle length) that formalizes the pattern recognition this post teaches by example.