A Wide QRS Tachycardia with Three Distinct Left Bundle Branch Block Morphologies in a Patient with Sinus Rhythm with Left Bundle Branch Block: What Is the Mechanism?

Simultaneous narrow and wide QRS complex tachycardia: Misdiagnosis or missed diagnosis?

“…The differential diagnosis of a WCT includes ventricular tachycardia (VT), all causes of NCT with aberrant conduction, and preexcited or antidromic tachycardias 8,17–23 . Since we detected the QRS prolongation with LBBB morphology response to programmed atrial stimulation as similar to the morphology of WCT (Figure 3), we had made the pre‐diagnosis of AVNRT with aberrancy for her second tachycardia.…”

Transition from two wide to a narrow QRS complex tachycardia: What is the mechanism of tachycardia and transition?

“…This suggests the presence of multiple fast/retrograde AV nodal pathways, 21 and these transitions could be related to the second slow pathway 22–24 . Therefore, the multiple forms of induced tachycardias with both RBBB and LBBB morphologies favor atypical AVNRT 6,17,18 …”

“…1 The differential diagnosis for the WCT includes all causes of NCT with BBB, all causes of NCT with antegrade pre-excitation, ventricular tachycardia (VT), and antidromic (ART) and other preexcited reciprocating tachycardias. [2][3][4][5][6][7][8] Antegrade activation suggests that the mechanism of the WCT is BBB, whereas retrograde activation is consistent with either VT or antidromic tachycardia (ART). 5,9 In the current case, the HV intervals during the WCTs were fixed and normal as did in sinus rhythm excluding the VT, ART and other preexcited reciprocating tachycardias.…”

“…The differential diagnosis of a short RP NCT with the earliest atrial activation in the HB region includes atrial tachycardia (AT) originating from near the AV node, orthodromic reciprocating tachycardia (ORT) using a septal accessory pathway, typical (slow‐fast form) atrioventricular nodal reentrant tachycardia (AVNRT), junctional tachycardia and orthodromic nodo‐fascicular (NF) or nodo‐ventricular (NV) reentrant tachycardia (NFRT/NVRT) 1 . The differential diagnosis for the WCT includes all causes of NCT with BBB, all causes of NCT with antegrade pre‐excitation, ventricular tachycardia (VT), and antidromic (ART) and other preexcited reciprocating tachycardias 2–8 …”

“…[22][23][24] Therefore, the multiple forms of induced tachycardias with both RBBB and LBBB morphologies favor atypical AVNRT. 6,17,18 It would be only speculative to make a concise correlation with anatomy since the AH change over a slow pathway might be both due to functional decremental conduction or perhaps more than one distinct anatomical slow pathway. In the presence of dual AV nodal pathways, the refractory period of the fast pathway is usually longer than that of the slow pathway.…”