Wide complex tachycardia in a patient with a dual-chamber defibrillator: What is the rhythm? A tale of timing cycles

Abstract

Case summary A 72-year-old patient with history of ischemic cardiomyopathy and dual-chamber implantable cardioverter-defibrillator (ICD) was evaluated for tachycardia. The patient had undergone surgery for implantation of a HeartMate II left ventricular assist device 1 week prior to the onset of tachycardia. Postprocedure, the patient was persistently in a wide complex tachycardia except during brief episodes, where his heart rate was 80 beats/ min, and the 12-lead electrocardiogram (ECG) of which is shown in Figure 1A. The faster rhythm was at 125 beats/min (Figure 1B) and below the tachycardia detection interval of the ICD. The telemetry strips corresponding to the 2 rhythms are shown in Figure 2. Can a definite diagnosis of his rhythm be obtained from the ECG and telemetry recordings, and what programmed pacing mode of the dual-chamber ICD can explain the findings?