An incessant repetitive tachycardia in a patient with prior AVNRT ablation: What is the mechanism?

Abstract

Figure 1 Spontaneous initiation of tachycardia. The first atrial beat of tachycardia is denoted by A*. Shown in the figure are electrocardiographic leads I, II, and V1 and intracardiac recordings from the high right atrium (HRA), a septal catheter placed just proximal to the His recording position along the atrial septum (Sept; p, m, and d for proximal, mid, and distal locations, respectively), and right ventricular (RV) apex. Case presentation A 69-year-old man with systolic heart failure and a remote history of successful slow pathway ablation for typical atrioventricular (AV) nodal tachycardia (AVNRT) underwent a diagnostic electrophysiology study because of a newonset incessant repetitive tachycardia with a left bundle branch block (LBBB) configuration. Multielectrode catheters were placed at the high right atrium, His bundle region, coronary sinus, and right ventricular (RV) apex. The baseline QRS morphology was an LBBB pattern, and the baseline sinus cycle length, QRS duration, AH interval, and HV interval were 765, 130, 85, and 60 ms, respectively. The tachycardia was consistently initiated after spontaneous premature ventricular beats or ventricular pacing (Figure 1). The first atrial beat of tachycardia (A*) had an atrial activation sequence similar to the preceding sinus beat. The QRS morphology during tachycardia was an LBBB pattern and was identical to the baseline QRS morphology. Ventricular stimuli delivered when the His bundle was refractory failed to advance the atrium. At the onset of tachycardia, there was often variability in the HH and the VV cycle length without a corresponding change in the AA interval (Figure 2). To confirm the mechanism of tachycardia, pacing was performed from the RV apex at cycle lengths just below the tachycardia cycle length (TCL). Figures 3A and 3B demonstrate RV pacing at 430 and 440 ms, respectively. Based on the information supplied on the onset of tachycardia, the spontaneous variability in the TCL, and