Evolutionary Jump In ICD Technology: Is Sub-Sternal ICD The New Star On Horizon?

Implantable cardioverter-defibrillators (ICDs) have an evolutionary history of around 30 years. Engineering advancements have shown the way forward from the conventional transvenous ICDs to subcutaneous (SQ) devices that overcome major limitations of transvenous systems like lead failure, vascular obstruction, systemic infections, etc. However, SQ devices have their own drawbacks like lack of anti-tachycardia pacing and sustainable pacing support.

The concept of implanting device leads in substernal space has the theoretical benefit of satisfactory sensing and pacing and lower defibrillation threshold than previous SQ systems. In this regard, a study published by Crozier et al. in JACC: clinical electrophysiology, has shown the first-in-human evaluation of a substernal extravascular (EV) ICD which has shown the feasibility of substernal lead placement, defibrillation, and pacing with a chronically implanted system.

In their prospective, nonrandomized, chronic pilot study conducted at 4 centers in Australia and New Zealand, 21 patients referred for ICD implantation received EV ICD systems. Investigators found that among 20 patients who underwent successful implantation, the median defibrillation threshold was 15J, and 90% passed defibrillation testing with a ≥10-J safety margin. This is at par with contemporary transvenous ICD systems. Mean R-wave amplitude was 3.4 ± 2.0 mV, mean ventricular fibrillation amplitude was 2.8±1.7 mV, and the pacing was successful in 95% at ≤10 V. There were no intraprocedural complications. Two patients also underwent elective chronic system removal since hospital discharge. In the 15 patients presently implanted, the systems are stable in long-term follow-up.

This the study concludes that the future novel EV ICD platform may enable physicians to provide bradycardia and ATP options and to defibrillate the heart with energy levels similar to those of current transvenous ICD platforms. On the basis of this favorable experience, a worldwide pivotal study has already begun, with results forthcoming.

The complete article can be viewed from https://www.jacc.org/doi/full/10.1016/j.jacep.2020.05.029.

(1)1. Crozier I, Haqqani H, Kotschet E, Shaw D, Prabhu A, Roubos N, et al. First-in-Human Chronic Implant Experience of the Substernal Extravascular Implantable Cardioverter-Defibrillator. JACC Clin Electrophysiol. 2020 Nov 1;6(12):1525–36.