In small, non-randomised studies, an entirely subcutaneous implantable cardioverter-defibrillator (ICD) consistently detected and converted ventricular fibrillation induced during electrophysiological testing, according to a study published in The New England Journal of Medicine (NEJM) in May 2010. The device also successfully detected and treated all 12 episodes of spontaneous, sustained ventricular tachyarrhythmia.
The study highlights the development and potential benefits of the S-ICD System (Cameron Health), the first minimally invasive, subcutaneous ICD, for the treatment of sudden cardiac arrest (SCA). In the studies, the S-ICD detected 100% of induced and spontaneous episodes of irregular heart rhythms.
The S-ICD System is unique because its implantation is entirely subcutaneous, eliminating the need for lead placement in or on the heart and simplifying the surgery by eliminating the need for imaging equipment. Transvenous ICDs require placement of at least one lead in or on the heart. Most frequently, these leads are threaded through a vein and placed in the heart, allowing for sensing of the heart’s rhythm and delivery of a life-saving electric shock when a harmful arrhythmia is detected. The surgical placement and ongoing presence of these transvenous leads within the patient’s heart are associated with a significant proportion of the complications related to this well-established and highly effective therapy.
“Transvenous implantable cardioverter defibrillators have proven to be an effective therapy for treating sudden cardiac arrest. As with any medical technology, however, there is room for improvement,” said Gust H Bardy, Seattle Institute for Cardiac Research, lead author of the NEJM paper and co-founder of Cameron Health. “These studies suggest that the S-ICD System is a viable alternative that may overcome some of the problems associated with transvenous ICDs in certain patients. The findings suggest that physicians now have an important new option to consider when evaluating patients for defibrillator therapy, and one that may reduce the barriers to adoption of this life-saving therapy.”
The NEJM publication highlights four studies of the S-ICD System. Two short-term trials designed to identify a suitable device configuration and assess energy requirements were followed by two longer-term trials designed to assess the efficacy of the S-ICD System in detecting and treating ventricular tachyarrhythmias in patients at risk of sudden cardiac death. The trials were conducted between September 2001 and November 2009. Results of the longer-term studies include 100% detection of induced arrhythmias and 98% conversion success for patients implanted with the S-ICD System, which is comparable to that seen with transvenous systems. In addition, ventricular tachyarrhythmias were detected and treated in 100% of 12 spontaneous episodes.
In the first of the short-term trials, four subcutaneous ICD configurations were evaluated in 78 patients who were candidates for ICD implantation. In the second of the short-term trials, the optimal configuration was then tested in 49 additional patients to determine the subcutaneous defibrillation threshold in comparison to the standard transvenous ICD, a pre-requisite in order to engineer the system so that it can deliver the necessary energies to restore the heart rhythm to normal. The optimal device configuration (using a lateral generator and a parasternal electrode) was as effective as a transvenous ICD but, as expected, had a significantly higher energy requirement (36.6 ± 19.8 joules vs. 11.1 ± 8.5 joules). Long-term implants were evaluated in a six-patient pilot study followed by a 55-patient single-arm trial. In the pilot study, a total of 18 episodes of ventricular fibrillation were induced, all of which were appropriately detected, and all sustained episodes of ventricular fibrillation were successfully converted. This initial experience confirmed the device’s overall utility and allowed the engineers to adjust the software. In the 55-patient, single-arm trial, all episodes of sustained ventricular fibrillation were appropriately detected, and 98% of patients satisfied implant testing criteria. This trial allowed further advances in lead system anchoring and software by study end.
The S-ICD System received CE approval in 2009. In the USA, Cameron Health is conducting an FDA pivotal trial. The first patient was enrolled on 3 March 2010. The trial, which is being conducted under an investigational device exemption, is a prospective, multicentre, single-arm design involving up to 330 subjects at up to 35 sites in the USA, Europe and New Zealand.
Appropriate candidates for S-ICD therapy may be those undergoing primary preventative treatment of cardiac arrest, such as those with a prior myocardial infarction or reduced ejection fraction, and those who are ventricular fibrillation survivors. Patients with congenital heart disease or genetic proclivities to sudden cardiac death, such as long QT syndrome or hypertrophic cardiomyopathy, as well as those with difficulties in venous access, may also prove to be candidates for this therapy. Patients with slow monomorphic VT or patients requiring antibradycardia pacing are not candidates. Other exclusion criteria may apply depending upon the patient’s circumstance. Physicians should discuss the potential for use of the S-ICD for their patients with knowledgeable electrophysiologists in their area.