Subcutaneous ICD Implantation

Electrophysiologists from the Hospital of the University of Pennsylvania were the first in the region to implant a new subcutaneous defibrillator system. The device implantation is part of an ongoing clinical trial; learn more about the system in this feature article.

Case Study

A 21-year-old asymptomatic male athlete was evaluated after his brother had survived a ventricular fibrillation (VF) episode at age 25. Physical exam was unremarkable. A 12-lead ECG (Figure 1) showed sinus rhythm with normal AV conduction. An unusual pattern of mid QRS fragmentation with T wave inversion in lead V1 and inferior leads was noted. A 2D echocardiogram showed a reduced left ventricular (LV) ejection fraction of 45% that failed to improve with exercise, without any other abnormal findings. A cardiac MRI with gadolinium and delayed enhancement showed a reduced LV function of 45% and reduced RV function of 40%. No evidence of late enhancement or other focal abnormalities were noted. His brother has the same pattern in the 12-lead ECG, with similar findings in imaging studies. Based on the family history and abnormal findings, a familial cardiomyopathy syndrome was suspected, and the decision was made to implant a primary prophylactic defibrillator. However, the patient and family were concerned about long-term intravascular lead problems and decided to participate in the S-ICD^® system (Cameron Health, Inc., San Clemente, CA) IDE clinical study. The subcutaneous implantable cardioverter defibrillator (S-ICD^®) is a new concept that uses a subcutaneous pulse generator and subcutaneous electrode system to treat ventricular tachyarrhythmias.

About the Study

The S-ICD system IDE clinical study, sponsored by Cameron Health, is designed to evaluate the safety (complication-free rate) and effectiveness (induced ventricular fibrillation conversion rate) of the S-ICD. It is a prospective, non-randomized, multicenter trial without a control group conducted in the United States, Europe and New Zealand. The duration of the study is 180 days, and patients will be followed at 30, 90 and 180 days and every 6 months until study completion in October 2015, with evaluation of spontaneous and conversion data. The estimated enrollment is 330 subjects.

S-ICD Implantation

The system consists of the SQ-RX™ pulse generator, Q-TRAK™ electrode, and Q-TECH™ programmer. The implant is a relatively straightforward outpatient procedure. Briefly, two small incisions are made in the left parasternal area to secure the distal (at the level of the second intercostal space) and proximal (at the level of the xyphoid process) sensing electrodes of the lead system that has been tunneled subcutaneously with a non-traumatic tool to position the coil parallel to and 1–2 cm to the left of the sternum. The pin connector end of the lead is tunneled to the pocket created in the left lateral chest at the level of the sixth rib between the mid axillary line and the anterior axillary line, where the pulse generator will sit (Figure 2). This is performed using anatomic landmarks without the use of fluoroscopy. Before VF induction, an auto-setup routine is performed in order to select the appropriate vector for sensing and obtain a template of the intrinsic QRS to avoid double QRS and T wave counting. The procedure also involves two VF inductions with successful defibrillation at 65 J (Figure 3). Typical detection time is approximately 15 seconds. Programming allows two zones. A conditional zone uses discriminator algorithms before considering therapy incorporating the QRS templates acquired during the auto-setup routine. A shock zone goes directly to therapy. The maximum rate cutoff is 250 bpm and the only programmable energy the device can deliver is 80 J. If the first shock is ineffective, a second shock can be delivered using reverse polarity. There is no ability for antitachycardia pacing; however, there is post-shock pacing via subcutaneous demand pacing for up to 30 seconds at 50 bpm. The device can deliver up to 5 consecutive therapies. Brady et al recently published their experience with the S-ICD.¹ First, they evaluated the best sensing configuration and concluded that the best configuration was that of a parasternal coil electrode with a left lateral pulse generator. Second, they compared a simultaneous S-ICD with a transvenous ICD system, with similar results in 49 patients. Next, they performed two trials of permanent S-ICD implantation; the first was a pilot trial of 6 patients in New Zealand, showing the acute testing in all patients with a submaximal shock of 65 J and no complications in the follow-up period. No spontaneous events were seen. A 55-patient trial in New Zealand and Europe was also included. Fifty-three patients had defibrillator testing and 52 patients had two successful consecutive 65 J shocks. One patient could not be defibrillated twice and underwent intravenous system implant. The procedure was performed in less than an hour and the mean time to shock was 14 ± 2.5 seconds. Two patients needed device explant due to infection and no device erosion was seen. No lead fractures or generator migration were seen. Three patients had lead dislodgment due to inadequate lead anchoring at the distal tip, and required surgical repositioning. One patient had a late lead dislodgment as a result of vigorous physical activity. Oversensing occurred due to inappropriate placement in the header, muscle noise, and change in QRS morphology; all these situations were resolved with reprogramming. Twelve episodes of ventricular tachycardia were successfully treated in follow up. No ventricular fibrillation was seen.

Summary

The S-ICD could be a new alternative for patients at risk of sudden cardiac death, although it is yet to be proven as safe and effective as other proven intravenous systems. It obviates the need of intravascular components, and hence eliminates the risk associated with leads in the vascular system. It is an outpatient procedure performed without the need for fluoroscopy. It has been shown to be effective in terminating induced VF and proven to be safe in New Zealand and Europe. The IDE study is ongoing in the US, and will add to the available data for this device. The limitations of this system may be related to the lack of pacing to terminate arrhythmias and an inability to “painlessly” terminate tachycardia. It also cannot be used if standard pacing indication is present. Nevertheless, it could be another option in the treatment of patients at risk of ventricular arrhythmias and sudden cardiac death.

Reference

1. Brady GH, Smith WM, Hood MA, et al. An entirely subcutaneous implantable cardioverter-defibrillator. N Engl J Med 2010;363:36–44.

Disclosure: The authors have no conflicts of interest to report.