Author + information
- Received August 19, 2015
- Accepted September 17, 2015
- Published online February 1, 2016.
- aArrhythmia and Electrophysiology Unit II, Humanitas Gavazzeni Clinics, Bergamo, Italy
- bHeart & Vascular Institute, Cleveland Clinic Abu Dhabi, Abu Dhabi, United Arab Emirates
- cArrhythmia and Electrophysiology Research Center, IRCCS Humanitas Research Hospital, Rozzano, Milan, Italy
- ↵∗Reprint requests and correspondence:
Dr. Hussam Ali, Arrhythmia and Electrophysiology Unit II, Humanitas Gavazzeni Clinics, Via M. Gavazzeni 21, 24125 Bergamo, Italy.
A 68-year-old woman with permanent atrial fibrillation and a VVI pacemaker underwent catheter ablation of the atrioventricular junction. Before ablation, pacemaker interrogation confirmed correct functioning and it was programmed to VVI backup-pacing at 35 bpm. While positioning the ablation catheter adjacent to the His bundle region, and before radiofrequency application, inappropriate pacing spikes were observed on electrocardiogram recording (Figure 1A, solid arrows). Reinterrogation of the device revealed remarkable deterioration of bipolar ventricular sensing leading to intermittent loss of sensing and inappropriate ventricular pacing (Figures 1B and 1C, solid arrows). Pacing threshold, lead impedance, and fluoroscopic position of the lead were all unchanged and optimal.
Interestingly, this device malfunction occurred immediately after the appearance of a mechanically induced right bundle branch block (RBBB). The consequent change of impulse direction, to a more perpendicular vector relative to the ventricular lead dipole, reduced markedly the bipolar voltage (Figures 1D and 1E). Noteworthy, ventricular sensing of likely premature beats (asterisks in Figures 1B and 1C) was not affected, apparently because the proximal RBBB did not influence their propagation pattern. After a short observation period, RBBB recovered and so did the bipolar ventricular sensing. Theoretically, unipolar sensing would not be affected by RBBB because the unipolar voltage is known to be independent of impulse direction (1). However, this sensing configuration is inappropriate in pacing-dependent patients.
Finally, this case highlights that RBBB could affect bipolar ventricular sensing with consequent pacemaker malfunction. In pacemaker patients, electrophysiologists should consider this potential phenomenon when performing ablation adjacent to the RBBB or if a new RBBB develops in any clinical scenario: spontaneously, rate-dependent, or during antiarrhythmic drug therapy. Careful device interrogation, and reprogramming when needed, is prudent to avoid potential device malfunction in these cases.
All authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- Received August 19, 2015.
- Accepted September 17, 2015.
- American College of Cardiology Foundation