Is a Totally Subcutaneous ICD Safe and Effective?
Abstract & Commentary
Edward P. Gerstenfeld, MProfessor of Medicine, Chief, Cardiac Electrophysiology, University of California, San Francisco
Source: Weiss R, et al. Safety and efficacy of a totally subcutaneous implantable cardioverter-defibrillator. Circulation 2013;128:944-953.
Multiple prospective, randomized trials have shown a mortality reduction in patients with reduced left ventricular ejection fraction who undergo prophylactic implantable cardioverter-defibrillator (ICD) therapy. However, enthusiasm for ICDs has been tempered by chronic lead complications, including infections, fracture, and insulation breach. Several ICD leads have been recalled by the manufacturer due to faulty manufacturing design, and require regular surveillance. The totally subcutaneous ICD is implanted extrathoracically, completely avoiding the intravascular space. The advantages to avoiding the intravascular system are clear. Limitations include the inability to perform pace-termination of ventricular tachycardia, the unclear effectiveness of defibrillation therapy clinically, and the larger size defibrillator generator. The current study is a prospective, nonrandomized, multicenter, observational study of patients undergoing implantations of the subcutaneous-ICD (S-ICD). Patients who had a standard ICD indication were enrolled. The primary safety endpoint was the 180-day S-ICD complication-free rate. The primary effectiveness endpoint was the acute induced ventricular fibrillation (VF) conversion rate during the time of implantation. Patients were followed up at 30, 90, and 180 days, and then semiannually. A total of 321 patients underwent S-ICD implantation; 276 patients had a follow-up duration > 180 days. Most patients (79%) underwent implantation for primary prevention of sudden death. The mean left ventricular ejection fraction was 36 ± 16%; 15% had atrial fibrillation and 41% had a prior myocardial infarction. The 180-day complication-free rate was 99%. The conversion rate of induced VF during implantation was 100%. This did not include 16 patients who were deemed not evaluable because of clinical circumstances, including hemodynamic instability, left ventricular thrombus, or inability to induce VF. There were eight deaths during the study period; five were deemed noncardiac, two were sudden, and one was unclear. A total of 119 spontaneous ventricular tachycardia (VT)/VF episodes occurred in 21 patients — 38 discrete VT/VF episodes and 81 episodes associated with VT storm in four patients. Of the 38 discrete VT episodes, 43 appropriate shocks were delivered. The S-ICD converted 35/38 episodes (92.1%) on the first shock and 37/38 (97%) episodes with one or more shocks. The remaining episode terminated spontaneously during charging. There were 18 device infections; four required device removal. The overall incidence of inappropriate shocks was 13.1%, for supraventricular tachycardia or oversensing of T waves, QRS complexes, or external noise. The mean time to therapy was 14.6 ± 2.9 seconds. The authors concluded that this study supports the efficacy and safety of the S-ICD system.
The ICD has revolutionized the treatment of sudden death, with the SCD-HeFT trial demonstrating a 7% absolute mortality reduction in all patients with EF < 35%, regardless of etiology.1 However, device morbidity has tempered enthusiasm for prophylactic ICD implantation by many physicians. The primary limitation of these devices has been the intravascular leads. Lead fracture and insulation break can lead to inappropriate painful shocks in some patients. Systemic infection typically requires device removal and lead extraction, which in itself poses life-threatening risks. The S-ICD can potentially alleviate these chronic lead concerns, particularly in young patients who are more active and face many years of potential lead problems, and in patients with prophylactic indications where the likelihood for receiving a shock and the need for antitachycardia pacing therapy is lower. The "leads" of the S-ICD are tunneled subcutaneously along the inferolateral border of the ribcage and sternum and attached to a generator placed in a pocket in the left mid-axillary line. The results thus far of the S-ICD have been promising. There were no patients in the study who did not have successful termination of a clinical episode of VT/VF. The safety of the S-ICD implant was also impressive. Finally, the inappropriate shock rate of 13% is lower than most intravascular ICD studies, and is likely to improve with better programming and detection algorithms. In my experience, the main current limitation is the large size of the subcutaneous can (145 gm), which lies along the lateral thoracic ribcage and can be quite prominent in thin patients. The battery longevity is also shorter than typical intravascular systems, estimated at 5-8 years.
Is the S-ICD ready for prime-time? In my opinion, the technology is promising, but the number of treated patients and VF episodes is still far too small to recommend implantation of the S-ICD over a traditional intravascular device. Patients with congenital heart disease without intravascular access or those with prior lead infections should be considered reasonable candidates. In the future, young patients with inherited cardiomypathies, such as Long QT syndrome and hypertrophic cardiomyopathy, would also be the most likely to benefit. Comparative trials between the S-ICD and standard intravascular ICD are being planned. Next-generation devices will undoubtedly be smaller and have longer battery longevity. Until more data arise, the implantation of the S-ICD should be limited. But over time, we will likely see a growing use of this promising technology.
REFERENCE
1. Bardy GH, et al. Amiodarone or an implantable cardioverter-defibrillator for congestive heart failure.N Engl J Med 2005;352:225-237.
