Tachycardia with QRS Morphology Identical to the Normal Sinus Rhythm Electrocardiogram: What is the Mechanism?

Abstract

VT, ablation, bundle branch reentry, left bundle branch tachycardia Case PresentationA 64-year-old man with a history of prior myocardial infarction, coronary artery bypass grafting, and ischemic cardiomyopathy with a left ventricular ejection fraction of 20% presented with a three-day history of palpitations and near syncopal episodes. The patient had a biventricular pacemaker-defibrillator (BiV-ICD) implanted 2 years prior and was taking amiodarone for a history of frequent defibrillator shocks. The device interrogation showed 102 episodes of tachycardia at a rate of approximately 160 beats/min over a 72-hour period. All of these episodes were terminated with antitachycardia pacing. Electrogram analysis of the BiV-ICD's stored arrhythmia events showed a tachycardia with a 2:1 ventriculoatrial (VA) relationship, which was initiated by a premature ventricular contraction (PVC) with a long-short coupling interval (Fig. 1A). A spontaneous episode of tachycardia was captured on hospital telemetry (Fig. 1B). The tachycardia had a left bundle inferior axis morphology and was initiated by PVC of a different morphology than the tachycardia itself. Baseline electrocardiogram (ECG) demonstrated sinus rhythm with biventricular pacing. The ECG with ventricular pacing turned off showed normal sinus rhythm with a left atrial abnormality, prolonged PR interval of 320 ms, and left bundle branch block (LBBB) pattern ( Fig. 2A). During the patient's electrophysiology (EP) study, the baseline intervals were as follows: atrial-His (HA) interval = 100 ms; His-ventricular (HV) interval = 95 ms; QRS = 160 ms; Baseline Cycle Length = 890 ms. A LBBB morphology tachycardia with a cycle length of 380 ms was easily induced with a single ventricular extrastimulus from the right ventricular apex. A 12-lead ECG of the