Subcutaneous cardioverter-defibrillator implantation in an adult with congenital heart disease and left infra-mammary pacemaker

Abstract

The approach/type of an implantable cardioverter defibrillator (ICD) is determined by the underlying cardiac anatomy, venous access, and pre-existing cardiac implantable electronic devices. We describe a case of subcutaneous ICD implantation in an adult with congenital heart disease (CHD) with a pre-existing inframammary transvenous pacemaker. This was preferred over adding a defibrillator coil to existing pacing leads, extraction/replacement of pacing system, or a sternotomy/epicardial ICD placement. The procedure was accomplished uneventfully with successful defibrillation threshold testing. Innovative approaches are required to manage arrhythmias in adults with CHD, with shared decision making playing a critical role.

1. Introduction

The implantable cardioverter-defibrillator (ICD) is an established therapy for the prevention of sudden cardiac death (SCD) [1]. Most ICD systems are implanted via a percutaneous transvenous (TV) approach, and can provide anti-bradycardia and anti-tachycardia pacing capabilities important for some patients. However, implantation of TV-ICDs is not feasible or advisable in patients with various anatomical obstacles including venous abnormalities or pre- or post-operative congenital heart disease (CHD) [2]. Instead, many such patients undergo open chest surgery for implantation of epicardial systems [3]. Unfortunately, the clinical course in patients with either of these systems may include implant-related complications, subsequent lead failure, device-associated infections, or vascular complications [4]. The introduction of the subcutaneous ICD (S-ICD) in 2010, implanted via an extra-thoracic and extra-vascular approach, has provided an attractive option for patients not requiring anti-bradycardia or anti-tachycardia pacing. Since then, progressively widespread use has shown the S-ICD is an important alternative to TV or epicardial ICD systems in patients with or without normal cardiovascular anatomy [2].

For each patient, particularly adults with post-operative congenital heart disease and a pre-existing TV or epicardial pacemaker, selecting the optimal approach to ICD implantation can be particularly challenging. Diverse congenital anomalies, the presence of surgical baffles, stenotic intracardiac channels, residual intracardiac shunts, and pre-existing pacing systems significantly impact the decision-making process. Herein we describe an adult with congenital heart disease with a pre-existing left-sided TV pacemaker with recurrent ventricular tachycardia who underwent successful S-ICD implantation and defibrillation threshold testing (DFT) despite the presence of an infra-mammary pacemaker generator in the shock vector.

2. Case report

A 47-year-old female with d-transposition of the great arteries s/p Mustard atrial switch surgery and sick sinus syndrome s/p TV pacemaker was referred for consideration of an ICD because of symptomatic non-sustained ventricular tachycardia (256 bpm) recorded on pacemaker interrogations (Fig. 1) despite beta-blocker therapy. Simply changing anti-arrhythmic medication seemed insufficient to eliminate risk for future cardiac arrest. Her dual chamber TV pacemaker had been implanted more than twenty years ago for sick sinus syndrome, with the generator located in a left infra-mammary position for cosmetic purposes. She had undergone three prior generator changes uneventfully. Recent 12-lead-electrocardiograms have shown a stable pattern of atrial-paced rhythm with intact AV conduction, right axis deviation, right ventricular hypertrophy/strain, QRS duration of 92 msec and QTc of 448 msec. Echocardiograms (including saline bubble contrast) demonstrated low-normal sub-systemic right ventricular systolic function, normal sub-pulmonary left ventricular systolic function, no significant valvular stenosis/regurgitation, patent superior and inferior Mustard systemic venous baffles and no intracardiac shunting. Programmed AAIR-DDDR 60/130, pacemaker interrogation showed 98 % atrial-paced rhythm, <5 % ventricular-paced rhythm, acceptable lead performances, and underlying sinus bradycardia with junctional escape rhythm at ∼40 bpm. Atrial and ventricular pacing were programmed bipolar with outputs of 3V and 4V @ 0.40 ms, respectively. The pulse generator battery estimated longevity predicted 3 years.

Fig. 1.

Dual chamber pacemaker interrogation demonstrating rapid non-sustained ventricular tachycardia in a 47 year-old patient with d-TGA s/p Mustard procedure.

Several options for implanting an ICD system were explored, including [1] adding a new TV ICD coil to the existing pacing system [2]; extraction/replacement of her current leads with a new TV ICD system [3]; maintaining her TV pacemaker but adding an epicardial ICD; and [4] implanting a S-ICD recognizing implantation challenges including that the pacemaker generator would likely be in the shock vector. Ultimately, she passed S-ICD screening test with atrial-pacing @ 60 and 130 bpm, and with AV pacing @ 60 and 130 bpm at outputs of 5V @ 0.40 ms, with the S-ICD generator to be located slightly inferior to conventional sites so the lead would lie inferior to the infra-mammary generator. Review of this strategy with industry representatives and engineers deemed this approach to be feasible with no obvious expectation for damage to the TV pacemaker system.

After extensive shared-management discussions with the patient and multiple team members, the S-ICD approach was pursued. S-ICD implantation was performed in a mostly routine manner. The generator was positioned as predicted in a slightly inferior location to allow tunneling from the sub-xiphoid to the lateral chest wall incision below the inframammary pacemaker generator. (Fig. 2). The first DFT was successful at 65 J with a shock impedance 59 Ω. The conditional-shock and shock zone were set at 180 and 220 bpm respectively, with post-shock pacing disabled. Post-procedure interrogation of the pre-existing TV pacemaker showed stable performance. She was discharged home the day after the procedure. Her anti-arrhythmic regimen was changed to sotalol to hopefully improve first line protection. At 6-month follow-up, evaluation confirmed appropriate wound healing and stable TV pacemaker and S-ICD performance.

Fig. 2.

Chest X-ray (AP and lateral) demonstrating somewhat inferiorly placed subcutaneous ICD location in relation to pre-existing transvenous inframammary pacemaker.

3. Discussion

Adults with congenital heart disease include a complex cohort with diverse forms of underlying CHD, prior cardiac surgeries and a higher burden of atrial and ventricular arrhythmias compared to same-aged adults without CHD [5]. Arrhythmia management in these patients requires tailoring therapy to each individual, managing various brady- and tachy-arrhythmias, and the risk for cardiac arrest and sudden death in some [6]. In this case, we describe successful S-ICD implantation and testing in an adult with congenital heart disease with a pre-existing left inframammary TV pacemaker implanted for sick sinus syndrome and the pacemaker generator located in the shock vector.

The incidence of ventricular arrhythmias or sudden cardiac arrest in TGA patients s/p atrial switch surgery is ∼ 2–9.5 % [7]. Implantation of an ICD is a Class I indication for adults with congenital heart disease with hemodynamically significant ventricular tachycardia after other interventions for residual lesions if meaningful predicted survival is > 1 year [7]. Our patient did not experience syncope or cardiac arrest with episodes of NSVT on beta blocker therapy, but the recorded episode of NSVT was quite rapid and rather prolonged (Fig. 1), and she endorsed palpitations and dizziness. Given our concern for risk of future events including cardiac arrest, we suggested proceeding with ICD implantation rather than simply adjusting anti-arrhythmia medications as that might provide insufficient protection. The patient elected to have an ICD implanted as part of a shared decision-making model.

We reviewed various options for how to proceed. A TV-ICD system could be achieved by adding an ICD coil to her existing pacemaker system or extracting her current pacing system and placing a new dual chamber TV ICD system. The simple addition of an ICD coil was not pursued given risk for systemic venous obstruction, particularly in the superior limb of the Mustard baffle with the presence of existing pacing leads [8,9]. Extraction and replacement of device leads could likely be accomplished, but the length of time the leads had been in place, the tortuous course crossing the Mustard baffle and mitral valve required for extraction, and risk for internal bleeding gave us pause [10]. The patient was reluctant to undergo an epicardial ICD implantation that would necessitate sternotomy or thoracotomy, extensive dissection, and the possibility of poorer long-term epicardial ICD coil performance [11].

Ultimately, we elected to implant an S-ICD system, recognizing procedural challenges including placing the S-ICD generator inferior to the existing pacemaker generator to optimize lead tunneling, and importantly, having a pacemaker generator in the ICD shock vector. Additionally, we were wary of potential crosstalk between the pre-existing TV pacemaker and the new S-ICD system. Crosstalk between S-ICDs and TV pacemakers most often occurs from over-sensing unipolar pacing stimuli, and can result in inappropriate shocks; this is extremely uncommon with bipolar pacing [12]. Furthermore, saturation of the S-ICD sense amplifier from unipolar pacing during ventricular arrhythmias can lead to VT under-sensing and failure to deliver appropriate therapy [13]. In our case, the pacing leads were programmed in the bipolar configuration, and pre-operative S-ICD screening did not demonstrate over-sensing with either atrial or dual chamber pacing at lower and upper tracking rates. A similar finding was confirmed post-implantation. While prior reports have described potential damage to pacemaker circuitry/malfunction with direct current cardioversion/defibrillation [14], reports pertaining to our specific clinical scenario are not published. Fortunately, the procedure was accomplished uneventfully, and initial DFT testing was successful. During DFT the pacemaker was programmed DOO @ 70 bpm at bipolar outputs of 5V @ 0.40 ms to evaluate for the possibility the S-ICD would sense pacing during ventricular fibrillation, which could lead to under-sensing the ventricular fibrillation and failure to deliver therapy. During DFT, none of the persistent DOO pacing was sensed by the S-ICD, and appropriate timely therapy was delivered. Testing of the pacemaker post-DFT demonstrated stable system characteristics. Our patient continues to do well clinically with stable S-ICD and pacemaker performance on serial follow-up.

4. Conclusion

Innovative approaches are often required to manage serious arrhythmias in adults with congenital heart disease. The presence of a pre-existing TV pacemaker including an infra-mammary pacemaker generator in the shock vector of a left-sided S-ICD did not preclude implantation, and there was no evidence of crosstalk or acute deleterious effects on the existing pacing system during the procedure including DFT. The patient has done well in the months post-implant. This approach obviated the need for addition of an ICD coil in the Mustard baffle with pre-existing pacing leads, lead extraction/replacement, or open chest surgery, each with important attendant risks.

Funding source

N/A.

Ethics approval

Institutional review board approval was obtained from the University of Louisville and Norton Children's Hospital. Waiver of informed consent was provided by the IRB (case report). The work described has been carried out in accordance with The Code of Ethics of the World Medical Association.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.