Sustained Tachycardia in a Cardiac Resynchronization Therapy Recipient: What Is the Mechanism of Tachycardia?

Abstract

A 67-year-old female with prior circumflex arterial territory myocardial infarction, impaired contractile function (ejection fraction 35%), coronary artery bypass grafting (CABG), renal transplantation with a well-functioning graft, and a cardiac resynchronization therapy defibrillator (CRT-D; Cognis, Boston Scientific, Natick, MA, USA) was seen in the device clinic with acute onset of breathlessness and palpitations. She has had a 1-year history of recurrent symptomatic ventricular tachycardia (VT), refractory to antiarrhythmic agents including amiodarone, and two unsuccessful endocardial ablations. Electrocardiography (ECG) shows an incessant, monomorphic broad complex tachycardia (cycle length of around 470 ms, right bundle branch morphology, right superior axis, and concordantly tall R waves in the chest leads) below the programmed VT detection zone, which was set at 400 ms (Fig. 1). BP was 100/60 mmHg. There was ventriculo-atrial dissociation with more ventricular than atrial events during tachycardia, confirming the diagnosis of VT. During attempts to terminate VT by overdrive pacing from the left ventricular (LV) lead, the electrograms in Figure 2(A) were recorded. Once VT was terminated by overdrive pacing, the following electrograms in Figure 2(B) were recorded during pacing from the