Europace Advance Access originally published online on March 14, 2006
Europace 2006 8(4):293-296; doi:10.1093/europace/euj047
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ICD
Unipolar ventricular pacing reduces inappropriate shocks from a separate cardioverter defibrillator in a post-Fontan patient
Department of Pediatric CardiologyPhoenix Children's Hospital1920 E. Cambridge Avenue, Suite 301, Phoenix, AZ 85006 USA
Manuscript submitted 10 October 2005. Accepted after revision 18 November 2005.
* Corresponding author. Tel: +1 602 253 6000; fax: +1 602 256 2878. E-mail address: mitchell_cohen{at}pediatrix.com
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Abstract |
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This report describes a 20-year-old man with complex congenital heart disease and inappropriate epicardial implantable cardioverter defibrillator (ICD) shocks secondary to double counting of ventricular-paced spikes and QRS complexes from a separate bipolar epicardial dual-chamber pacemaker. Adjusting to a unipolar paced-ventricular mode resolved any double counting via pacemaker–ICD interaction.
Key Words: Pacemaker, ICD, Fontan, Unipolar/bipolar
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Introduction |
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Bradyarrhythmias and tachyarrhythmias represent a cause of significant morbidity and mortality in patients following the Fontan procedure.1
Bradyarrhythmias typically consist of acquired sinus-node dysfunction from surgical incisions or injury to the sinus-node artery during the Fontan or staged Fontan operation. Although endocardial pacing is preferable to epicardial pacing because of lower pacing thresholds, a transvenous approach to place ventricular leads is generally not feasible, secondary to anatomical barriers which are congenital or created by the surgery itself. Placement of an automatic internal cardioverter defibrillator in this patient population involves an epicardial approach. |
Clinical presentation |
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The patient is a 20-year-old man with a history of single ventricular physiology with L-transposition of the great vessels. At 3 years of age, he underwent an atriopulmonary Fontan followed by a revision to a pericardial extracardiac Fontan in 1997, secondary to refractory atrial arrhythmias and ventricular dysfunction. Simultaneous with the Fontan revision, he underwent placement of a dual-chamber epicardial pacemaker for sinus-node dysfunction and acquired high-grade atrioventricular (AV) block secondary to ventricular inversion (L-looped). Following the Fontan revision, the patient had improved clinically, was playing golf and jogging three times per week, and was on digoxin, lisinopril, and coumadin. The patient had been at this baseline state of health until he sustained a syncopal episode while running in an airport. He was noted to be pulseless and cardiopulmonary resuscitation (CPR) was instituted by a nearby paramedic. The patient was intubated and noted at that point to be in an AV sequential rhythm. The patient's underlying rhythm is high-grade AV block with a ventricular escape of 50 bpm. He was taken to a local hospital where a CT scan revealed a mandibular fracture but no neurological injury. He was lucid but amnesic from the event. He was transferred to Phoenix Children's Hospital in stable condition. Interrogation of the dual-chamber pacemaker (Thera DR 7960, Medtronic, Minneapolis, MN, USA) did not detect any episodes of recent mode switching and the atrial- and ventricular-pacing/sensing thresholds were acceptable, though the battery was approaching elective replacement indicators. There was no evidence of intermittent loss of capture while on telemetry in the hospital prior to undergoing ICD implantation. No changes were made in his antiarrhythmic regimen. On the basis of the earlier events, a decision was made to implant a dual-chamber epicardial defibrillator, given the need for nearly 100% AV sequential pacing.
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Operative course |
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Approximately 5 days later, the patient underwent a complete sternotomy for placement of the ICD system. Given the significant scar tissue from multiple congenital heart surgeries, steroid-eluting suture-on ventricular leads had unacceptably high pacing thresholds and could not be used. Two unipolar non-steroid epicardial ventricular leads (Medtronic 5071) were implanted and adapted to form a bipolar system (implant thresholds: 0.5 ms/1.7 V; R-waves: 9.9 mV). A single epicardial patch (HVB, Medtronic 6721M) was placed on the posterior-lateral aspect of the ventricle and attached to a Marquis DR 7274 (Medtronic) automatic internal cardioverter defibrillator implanted in the left subrectus location. The original atrial lead (Medtronic Capsure Epi 4965) was also adapted with a new atrial Medtronic 5071 screw-in lead to form the bipolar atrial pace/sense lead (implant thresholds: 0.5 ms/1.0 V). Again, new steroid-eluting atrial leads were not used because of poor pacing thresholds from scar tissue around the Fontan baffle. After connecting the leads to the ICD, atrial sensing was not adequate in a bipolar configuration. Unipolar sensing/pacing became our only option, and therefore, the ICD could no longer serve as the primary pacing system in the atrium.
In order to implant a separate pacing system, the original ventricular epicardial lead (Medtronic Capsure Epi 4965), which had acceptable pacing thresholds, was connected to a new Medtronic 5071 lead to form the bipolar ventricular-pace/sense lead (implant thresholds: 0.5 ms/1.0 V; R-waves: 21 mV) to minimize any potential pacemaker/ICD interactions. Transmural leads were not employed, given the potential for embolic events. The atrial and ventricular leads were adapted to a bipolar pacemaker (Medtronic Kappa KDR 921) and tunnelled to a right subrectus pocket. Ventricular fibrillation was induced with successful defibrillation at 20 J on two separate occasions. Intraoperative testing of the ICD did not detect any double counting or inappropriate sensing with DDD bipolar pacing. During the same defibrillation testing, the pacemaker continued to function appropriately after the delivered shock. The patient tolerated the procedure and was extubated in the intensive care unit and discharged home 48 h later with no observed periods of inappropriate pacing or false ICD detection either on lying or walking.
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Clinical follow-up |
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Six weeks following implantation of the ICD, the patient developed increasing ventricular-pacing thresholds (5.5 V/0.21 ms), which transiently responded to oral steroids before stabilizing at 5.0 V/0.4 ms (bipolar impedance 712
). The atrial thresholds remained relatively constant (3.0 V/0.21 ms). Routine assessment showed AV sequential pacing with no double counting or oversensing on the ICD. Over the first few months post-implant, the patient was AV sequentially paced 
89% and atrially sensed-ventricular paced the remaining 11% of the time. Three months later, while walking briskly, the patient experienced six inappropriate ventricular fibrillation (VF) detections and defibrillations (Figure 1A and B). The patient was evaluated and observed to have intermittent double counting of the bipolar ventricular-pacing spike (5.0 V/1.0 ms), resulting in pseudo-VF detection and defibrillation. Attempts at lengthening the detection interval did not resolve the immediate problem, as there was one additional episode of an inappropriate shock 2 days later. Discontinuing atrial pacing and changing to a VVI-paced mode did not resolve the problem of double counting. As such, it was believed that the ventricular-paced mode was solely responsible for the multiple counting of the ventricular-pacing spikes and/or the evoked response with resultant delivery of inappropriate ICD therapy. Altering the ventricular pacing on the dual-chamber epicardial pacemaker to a unipolar mode abolished all double counting and inappropriate sensing (Figure 2). Ventricular-pacing thresholds in a unipolar mode revealed 100% capture at 5.5 V/0.15 ms (unipolar impedance: 442 ). Testing in a bipolar atrial-paced/unipolar ventricular-paced mode was performed with the patient supine, standing, squatting, and running with the programmer head over the ICD. In all these physiological states, there did not appear to be any double counting or oversensing while the ventricular lead was programmed unipolar pace/bipolar sense. Worst case scenario was also performed with unipolar ventricular pacing temporarily programmed at 7.5 V/1.5 ms, with no resultant double counting. In the last 6 months, the patient has resumed normal activities, including golf, and has not had any inappropriate shocks. Multiple reviews have also confirmed the absence of any oversensing or double counting of the ventricular-pacing spike and resultant QRS complex.
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Discussion |
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Algorithms designed to sense small amplitude signals rapidly during ventricular fibrillation but not to oversense noise, T-wave artefact, or pacemaker spikes in the absence of tachyarrhythmias are critical for the proper function of a cardioverter defibrillator. With the advent of new generation dual-chamber ICDs, double counting of both the pacemaker pulse and the resultant ventricular electrograms are largely of historical significance. Dual-chamber pacemaker–defibrillators provide not only improved diagnostic capabilities but also the benefits of dual-chambered pacing, rate responsiveness, and mode switching. In the patient discussed with complex congenital heart disease, ventricular dysfunction, and sinus-node dysfunction, dual-chamber pacing was required. However, because of the limitations imposed by poor bipolar atrial sensing, a separate dual-chamber epicardial pacemaker was implanted.
Prior to the development of transvenous bipolar pacing leads, unipolar pacing in conjunction with transvenous single chamber defibrillators occasionally resulted in double counting and inappropriate shock delivery.2,3 It was generally recommended in late 1990s that transvenous bipolar pacing systems be used in conjunction with separate ICDs. However, if it was not feasible to convert from unipolar to bipolar pacing, then the ICD bipolar pace/sense lead should be positioned in the interventricular septum or right ventricular outflow tract to achieve a maximum distance from the unipolar pacing lead.4,5 For the reasons of double counting and inappropriate shocks, unipolar pacing has generally been avoided with current generation ICDs. Although patients having undergone Fontan completion for a variety of single ventricle malformations cannot have an endocardial ventricular-pacing system as a result of venous barriers, epicardial brady pacemakers in this subset appear to function equally well as other epicardial systems in children with two ventricles.6 In this case, intraoperative testing of the ICD did not detect double counting or significant far-field noise resulting from the bipolar DDD pacemaker. Over the first few months post-implant, higher ventricular-pacing thresholds necessitated increasing output to assure ventricular capture. As a result of higher pacing thresholds, double counting by the ICD of the bipolar pacemaker spike and QRS complex resulted in a series of inappropriate shocks. The intermittent nature of the double counting may have been temporarily related to scar formation after implant causing local conduction delay. The change to a unipolar paced-ventricular mode and alteration in the vector of electrical activation relative to the ICDs sensing dipole appeared to resolve any double counting by the ICD in multiple physiological positions and activities. The unipolar paced-ventricular spike appeared to the ICD sense circuit as a contiguous signal with the QRS complex, thus eliminating the double counting.
This is the first reported case in which changing from a bipolar to unipolar epicardial paced mode resolved the problem of oversensing and inappropriate shocks seen with a single chamber epicardial defibrillator in a young adult with complex congenital heart disease. The understanding of the complex interaction between the two separate devices in this case allowed for the appropriate resolution of double counting and false shocks without the need for additional surgery.
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References |
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[1] . Driscoll DJ, Offord KP, Feldt RH, et al. Five- to fifteen-year follow-up after Fontan operation. Circulation 1992; 85: 469–96.
[2] . Calkins H, Brinker J, Veltri EP, et al. Clinical interactions between pacemakers and automatic internal cardioverter defibrillators. J Am Coll Cardiol 1990; 16: 666–73.[Abstract]
[3] . Cohen AI, Wish MH, Fletcher RD, et al. The use and interaction of permanent pacemakers and the automatic internal cardioverter defibrillator. Pacing Clin Electrophysiol 1988; 11: 704–11.[CrossRef][Medline]
[4] . Mattke S, Markewitz A, Muller D, et al. The combined transvenous implantation of cardioverter defibrillators and permanent pacemakers. Pacing Clin Electrophysiol 1997; 20: 2775–82.[CrossRef][Medline]
[5] . Haffajee C, Casavant D, Desai P, Moon R, Voukydis P, Pacetti P. Combined third-generation implantable cardioverter defibrillator with permanent unipolar pacemakers: preliminary observations. Pacing Clin Electrophysiol 1996; 19: 136–42.[Medline]
[6] . Cohen MI, Vetter VL, Wernovsky G, et al. Epicardial pacemaker implantation and follow-up in patients with a single ventricle after the Fontan operation. J Thorac Cardiovasc Surg 2001; 121: 804–11.
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