Although Implantable Cardioverter-Defibrillators (ICDs) are an established treatment for the prevention of death from ventricular arrhythmia, they require transvenous lead implantation and thus their insertion is prone to complications.  If cardiac pacing is not also required, then potentially transvenous electrodes can be avoided altogether.  The authors report the results of a novel subcutaneous ICD system designed to avoid the need for electrodes within or on the heart.
The authors initially conducted two short-term clinical trials to find a suitable device.  Four subcutaneous ICD configurations were tested in 78 patients and subsequently the best configuration was tested in an additional 49 additional patients to determine the optimal subcutaneous defibrillation threshold.  Following this, the long-term use of subcutaneous ICDs were tested in a pilot study involving initially 6, then 55, patients.
A parasternal electrode and a left lateral thoracic pulse generator were found to constitute the optimal device, and this configuration was found to be as effective as a transvenous ICD for terminating ventricular fibrillation; however, a significantly higher mean energy requirement was needed (36.6J vs 11.1J).  For those patients who received a permanent subcutaneous ICD, ventricular fibrillation was successfully detected in 100% of 137 episodes; after a mean of 10 months the device had successfully detected and treated all 12 episodes of spontaneous sustained ventricular tachycardia.

Conclusions:
In preliminary proof-of-concept studies, an entirely subcutaneous ICD device successfully detected and converted ventricular fibrillation and tachycardia.  Larger scale clinical trials are now indicated.

•    Bardy GH, Smith WM, Hood MA, Crozier IG, Melton IC, Jordaens L, et al. An entirely subcutaneous implantable cardioverter-defibrillator. N Engl J Med 2010, May 12.
Journals scanned
American Journal of Medicine; American Journal of Physiology: Heart and Circulatory Physiology; Annals of Emergency Medicine; Annals of Thoracic Surgery; Archives of Internal Medicine; BMJ; Chest; European Journal of Cardiothoracic Surgery; JAMA; Journal of Clinical Investigation; Journal of Diabetes and its Complications; Journal of Immunology; Journal of Thoracic and Cardiovascular Surgery; Lancet; Nature Medicine; New England Journal of Medicine; Pharmacoeconomics; Thorax

Reviewers
Dr Alistair C Lindsay, Dr Hussain Contractor