Progress in subcutaneous lead ICD devices

Conventional ICDs are a well established therapy for preventing death from ventricular arrhythmias, however because they rely on transvenous leads for sensing and defibrillation they have associated complications. Lead insertion can result in pneumothorax, haemothorax, and cardiac tamponade. Difficulties in achieving venous access may result in prolonged and unsuccessful procedures. Similarly, lead failure can generate either inappropriate shocks or impede appropriate treatment.
S-ICDs have been under development for several years and a leading Californian company, Cameron Health Inc, last year received CE approval for its S-ICD system.

Interest in the device was boosted by a recent study in the New England Journal of Medicine (1) from Dr Gust Bardy and others. Using this system they evaluated four subcutaneous ICD configurations in 78 candidates for ICD implantation and subsequently tested the best configuration in 49 additional patients to determine the subcutaneous defibrillation threshold in comparison with that of the standard transvenous ICD. They also evaluated long-term use of S-ICDs in a pilot of six patients, which was followed by a European trial involving 55 patients.

The best device configuration consisted of a parasternal electrode and a left lateral thoracic pulse generator, similar to that illustrated. This configuration was as effective as a transvenous ICD for terminating induced ventricular fibrillation (VF), but requiring a significantly higher mean energy requirement, 36.6 versus 11.1 Joules.

Among those who received a permanent S-ICD, VF was successfully detected in all 137 induced episodes. Induced VF was terminated twice in 58 of 59 patients with the delivery of 65 Joules in two consecutive tests.

In the European single-group trial of 55 patients (53 of whom were evaluated) the mean time to delivery of a shock was 14 secs. The mean duration of the procedure, including device insertion and testing, was 67 mins, a time which was reduced to 55 mins by practitioners who had done at least three implantations. After ten months follow-up 54 of 55 patients were alive, one having died from renal failure. A pocket infection developed in two patients but no cases of pocket erosion occurred. There were no lead fractures and no generator migration occurred.

The new device is reported to cost around £12,000 and does not need replacement for five years.

Speaking at a meeting in London recently, Dr Andrew Grace, Consultant Cardiologist, Papworth Hospital, Cambridge, UK, described leads as “the Achilles heel of defibrillator therapy”. He described also how about 36% of shocks from conventional ICDs are inappropriate. “This is absurd” said Dr Grace, who helped develop the new device and who is also a senior author on the NEJM paper.

He summarised the benefits of the new device saying that it delivered significantly fewer false shocks, it was faster to implant and safe to remove. It also eliminated the need for fluoroscopic guidance for lead placement and it “leaves the venous system alone”.

The device is approved in the UK and approximately 50 have been implanted.

Reference

1. Bardy GH, Smith WM, Hood MA et al. An entirely subcutaneous implantable-defibrillator. New Engl J Med 2010. ((10.1056/NEJMoa0909545) published 12 May 2010.

We will feature news about subcutaneous lead ICDs again in the near future.  We will also soon feature news about newer ICD systems which are also less prone to inappropriate shock delivery

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