Repetitive pacemaker-mediated tachycardia occurring only during left ventricular pacing: What is the mechanism?

Abstract

A 54-year-old man with an artificial aortic valve and a history of hemodynamically unstable sustained ventricular tachycardia was admitted for placement of an implantable cardioverter-defibrillator (ICD). The patient had an enlarged left ventricle, low ejection fraction (35%), left bundle branch block, QRS 195 ms, and low exercise tolerance. A biventricular ICD (Kronos LV-T, Biotronik, Berlin, Germany) was implanted with the left ventricular (LV) lead in the posterolateral vein. Two days later, predischarge evaluation by chest x-ray film revealed stable positions of the right ventricular (RV), LV, and atrial leads. Detailed device checkup confirmed good thresholds and sensing in all chambers. However, immediately after the device was programmed to DDD LV pacing only (basic rate 60 bpm, upper tracking rate 130 bpm), an arrhythmia appeared (Figure 1). These episodes of tachycardia took the form of repetitive salvos that were interspersed with one to a few LV-paced beats at a rate of 70 bpm. This profile was repeated each time the pacing mode was changed from either DDD BiV or DDD RV to DDD LV. Reprogramming to DDD BiV or DDD RV pacing always abolished the arrhythmia and prevented its recurrence. Figure 2, Figure 3 show intracardiac ECGs with event markers during the arrhythmia, sinus rhythm, and RV, LV, and BiV pacing. What was the mechanism of the tachycardia? Figure 2Shown from top to bottom are event markers, surface ECG, and atrial and right ventricular (RV) intracardiac electrograms. Note that atrial oversensing artifacts (AS) appear 300 ms after left ventricular pacing (VP) but only 60 ms after the peak of the RV intracardiac deflection. View Large Image Figure Viewer Download Hi-res image Figure 3Shown from top to bottom are event markers, surface ECG, and atrial and right ventricular (RV) intracardiac electrograms. A: Left ventricular (LV) pacing. Tachycardia terminates for one beat and then resumes. Termination coincides with sensing of intrinsic atrial depolarization. B: LV pacing. As the degree of fusion becomes smaller, atrial oversensing artifacts (ARS) appear progressively further from the LV pacing artifact (VP)—60, 200, and 280 ms—with the last artifact (AS) falling outside the postventricular atrial refractory period. However, regardless of the distance from the beginning of the QRS, the oversensing artifacts always follow RV intracardiac deflection with a constant coupling of 60 ms. C: During RV pacing, atrial oversensing artifacts (ARS) appear 120 ms after the RV pacing artifact (VP). D: During conducted atrial depolarization, atrial oversensing artifacts (AS) appear 80 ms after commencement of the QRS. E: During biventricular pacing, atrial oversensing artifacts (ARS) appear 130 ms after the pacing artifact (VP). View Large Image Figure Viewer Download Hi-res image