Tachycardia With Typical Left Bundle Branch Block Morphology and VA Block: What is the Differential Diagnosis?

Abstract

A 63-year-old man developed left bundle branch block (LBBB) several hours after percutaneous coronary intervention of the left anterior descending artery for a non-STsegment elevation myocardial infarction (Figs. 1A and B). Echocardiography revealed a normal left ventricular size, with an ejection fraction of 40%. After developing LBBB, he began experiencing recurrent sustained, but hemodynamically tolerated, wide-complex tachycardia, initiated by either atrial or ventricular premature complexes (Fig. 1C). On one occasion, the tachycardia persisted for over an hour and was terminated with intravenous adenosine. What is the differential diagnosis for this wide-complex tachycardia, and what findings and maneuvers can help differentiate one mechanism from the other in the electrophysiology laboratory? CommentaryThe tachycardia had an LBBB morphology that was identical to that seen during sinus rhythm, suggesting that this was a supraventricular tachycardia (SVT) with aberrancy. At the same time, VA Wenckebach was present (most evident in the inferior leads), indicating that the atria were not required for perpetuation of the tachycardia and suggesting that this was ventricular tachycardia (VT). The differential diagnosis for an SVT that would not require the atria and have a typical LBBB morphology is limited and includes (a) aberrantly conducted AV nodal reentrant tachycardia (AVNRT) with an upper common pathway, (b) aberrantly conducted orthodromic reciprocating tachycardia (ORT) utilizing a concealed nodofascicular or nodoventricular bypass tract, (c) aberrantly conducted nonreentrant junctional tachycardia (JT), (d) aberrantly conducted intra-Hisian reentry, and (e) antidromic reciprocating tachycardia utilizing a nodofascicular bypass tract. On the other hand, if this were VT, the differential diagnosis would include (a) bundle branch reentrant (BBR) VT utilizing the right and left bundle branches for its anterograde and retrograde limbs, respectively, and (b) intramyocardial VT originating or exiting near the exit of the right bundle branch.Interestingly, a few hours prior to the electrophysiologic study, the LBBB resolved completely, and since that time no more spontaneous runs of the wide-complex tachycardia were observed. In the electrophysiologic study, the atrial-His and His-ventricular (HV) intervals were 80 and 55 ms, respectively. There was no evidence of dual AV nodal physiology or AV accessory pathway. A wide-complex tachycardia similar to his spontaneous tachycardia was reproducibly induced with double atrial extrastimuli. It had an average cycle length of 400 ms (range: 350-450 ms) and typical LBBB morphology, and demonstrated both VA Wenckebach and 2:1 VA block. Induction of the tachycardia only occurred when the atrial extrastimuli conducted with LBBB and produced some HV prolongation (Fig. 2). During the tachycardia, there was a His bundle potential preceding every QRS complex, and the HV interval (48-50 ms) was consistently shorter than the HV interval produced by any of the atrially conducted ...

Diagnosis and Ablation of Multiform Fascicular Tachycardia

“…While a HV interval during BBRT shorter than that during SR is unusual in typical BBRT, the critical/slow limb in this case is presumed to be the septal fascicle with relatively preserved His and RBB conduction. The short HV is due to parallel activation of recording site on the His bundle and the RBBB, which has been previously reported 16 …”

“…Figures 1, 2, and 3 highlight common findings and principles in our series of cases. In all cases, the following observations were noted: (1) a reentrant mechanism for VT was confirmed by fulfilling at least one entrainment criteria; 16 (2) initial, spontaneous, clinical VT was noted to have RBBB QRS with left superior (LS) axis, although Cases 5 and 6 additionally had spontaneously shifting VT morphology to RBBB with right inferior (RI) axis; (3) FP preceded QRS in all VT forms that did not exhibit left bundle branch block (LBBB), and changes in the tachycardia cycle length (TCL) were preceded by changes in FP‐FP timing; (4) in non‐LBBB VT morphologies, entrainment pacing from the right ventricle (RV) or from the right bundle branch (RBB) resulted in a postpacing interval (PPI) that was greater than 30 milliseconds compared with the TCL, excluding the RBBB as part of the circuit.…”