Spontaneous Transition of Wide QRS Tachycardia: What Is the Mechanism?

Abstract

Case PresentationA 73-year-old man with a prior anterior myocardial infarction (MI; left ventricular ejection fraction 30%) experienced recurrent ventricular tachycardia (VT). He was referred to our hospital for implantation of an implantable cardioverter defibrillator (ICD). On admission, the electrocardiogram (ECG) showed sinus rhythm with right axis deviation and right bundle branch block (RBBB) morphology, and presence of old extensive anterior MI (Fig. 1A). During the electrophysiological study, two types of monomorphic VT (VT1, VT2) were induced by programmed ventricular stimulation during isoproterenol infusion. VT1 had QRS morphology of RBBB with northwest axis ( Fig. 1B; cycle length [CL], 400 ms), whereas VT2 had QRS morphology of RBBB with abnormal left axis deviation ( Fig. 1B; CL 350 ms). A 3.5-mm irrigated-tip catheter (ThermoCool, Biosense Webster, Diamond Bar, CA, USA) was introduced into the left ventricle along the left posterior fascicle (LPF) during VT1 (Fig. 2C). The LPF-LPF intervals dictated subsequent interventricular (V-V) intervals with atrioventricular dissociation, and the activation sequence of the LPF was from proximal to distal (Fig. 2D). In addition, the Hisventricular (HV) interval was 65 ms during sinus rhythm ( Fig. 2A) and decreased to 40 ms during VT1 (Fig. 2B). VT2 was similar to VT1 in that the LPF-LPF intervals dictated subsequent V-V intervals with atrioventricular dissociation, and the activation sequence of the LPF was from proximal to distal (Fig. 2D). Postpacing interval (PPI) from the right ventricular apex (RVA) was equal to tachycardia CL during VT2 (Fig. 3). Interestingly, spontaneous transition from VT1 to VT2 or vice versa was observed (Figs. 1B and 2D). Figure 2D shows intracardiac electrogram during a transition from VT2 to VT1. On the basis of these observations, what were the mechanisms of VT1 and VT2, and their transition?Commentary Atrioventricular dissociation during wide QRS tachycardia precludes most forms of supraventricular tachycardia as a diagnosis. Mechanisms of VT are either focal or macroreentry. In this context, specific macroreentry mechanisms would include scar-related reentry, bundle-branch reentry, interfascicular reentry, and intrafascicular reentry.During both VT1 and VT2, the LPF-LPF intervals dictated subsequent V-V intervals, and the activation sequence of the LPF was from proximal to distal. This observation indicated that the circuit of these VTs included the His-Purkinje system, whereas scar-related reentrant VT was excluded. Although automatic fascicular tachycardia originating from the LPF is considered as the mechanism of VT, the initiation of tachycardia by programmed stimulation is inconsistent with automatic mechanism. In left posterior Purkinje reentry (intrafascicular VT; IntraFVT), presystolic Purkinje potentials are recorded earlier in the distal portion than those in the basal portion; therefore, the sequence is in the reverse direction to that in bundle branch reentrant VT (BBRVT) or interfascicular VT (InterFVT, Fig. 4).1...