Purely subcutaneous implantable defibrillator (S-ICD)

Purely subcutaneous implantable defibrillator (S-ICD)

Purely subcutaneous implantable defibrillator (S-ICD): Conventional implantable defibrillators have a subcutaneous device and lead which is placed within the heart, through the venous system. Gust H Bardy, Warren M Smith, Margaret A Hood, Ian G Crozier, Iain C Melton, Luc Jordaens, Dominic Theuns, Robert E Park, David J Wright, Derek T Connelly, Simon P Fynn, Francis D Murgatroyd, Johannes Sperzel, Jörg Neuzner, Stefan G Spitzer, Andrey V Ardashev, Amo Oduro, Lucas Boersma, Alexander H Maass, Isabelle C Van Gelder, Arthur A Wilde, Pascal F van Dessel, Reinoud E Knops, Craig S Barr, Pierpaolo Lupo, Riccardo Cappato and Andrew A Grace evaluated an entirely subcutaneous ICD and reported the preliminary results in NEJM [1]. Initially they compared the thresholds for various configurations in 78 patients and later the best configuration in 49 patients to determine the subcutaneous defibrillation threshold in comparison with conventional ICD. Then they went on to a pilot study of long term use in 6 patients and finally a trial involving 55 patients. The best configuration was found to be one with a parasternal electrode and an ICD can location in the left lateral thoracic region. It was effective in terminating ventricular fibrillation with a higher energy requirement compared to transvenous lead systems (36.6±19.8 J vs. 11.1±8.5 J).Ventricular fibrillation was successfully detected in all the episodes induced. Two cases of pocket infection and four lead revisions were required in the trial. During the follow up period of 10 months, 12 episodes of spontaneous sustained ventricular tachyarrhythmias were detected and treated. Larger randomised studies of longer duration are needed to see if this entirely subcutaneous ICD will become a viable option for patients with life threatening arrhythmias. If it shown to be useful, it will avoid a lot of problems due to transvenous leads which could occur during the implantation as well as on long term follow up. Though transient back up pacing is available in an entirely subcutaneous system, long term anti bradycardia pacing is not feasible in this system. Similarly anti-tachycardia pacing (for slower ventricular tachycardias) is also not available.

2015 European Society of Cardiology (ESC) guidelines has given a class IIa recommendation for S-ICD in patients with indication for ICD, but not requiring pacing for bradycardia, antitachycardia pacing or cardiac resynchronization therapy. American Heart Association guidelines gave a class I recommendation for patients with complex anatomy and venous access problems or in those at high risk of infections, in need of ICD therapy [2]. These decisions are based on large registry data documenting utility in secondary prevention.

References

1. Gust H Bardy, Warren M Smith, Margaret A Hood, Ian G Crozier, Iain C Melton, Luc Jordaens, Dominic Theuns, Robert E Park, David J Wright, Derek T Connelly, Simon P Fynn, Francis D Murgatroyd, Johannes Sperzel, Jörg Neuzner, Stefan G Spitzer, Andrey V Ardashev, Amo Oduro, Lucas Boersma, Alexander H Maass, Isabelle C Van Gelder, Arthur A Wilde, Pascal F van Dessel, Reinoud E Knops, Craig S Barr, Pierpaolo Lupo, Riccardo Cappato, Andrew A Grace. An entirely subcutaneous implantable cardioverter-defibrillator. N Engl J Med. 2010 Jul 1;363(1):36-44.
2. Elif Kaya, Tienush Rassaf, Reza Wakili. Subcutaneous ICD: Current standards and future perspective. Int J Cardiol Heart Vasc. 2019 Aug 8;24:100409.