Subcutaneous ICD: Current standards and future perspective

Abstract

The subcutaneous implantable cardioverter-defibrillator (S-ICD) system is an established therapy for prevention of sudden cardiac death (SCD) and an alternative to a transvenous implantable cardioverter-defibrillator (ICD) system in selected patients. Since introduction of S-ICD in 2010, the device has undergone further development. Based on the unique feature of an entirely extracardiac implantation, S-ICD is able to reduce the known common perioperative and long-term complications of conventional transvenous implanted ICD systems. Especially for patients with a complex anatomy and no option of an endovascular lead implantation, the S-ICD offers a potential alternative. Initial uncertainty existed, questioning whether this ICD approach would be reliable in detecting and terminating ventricular arrhythmias. Multiple clinical studies, however, provided evidence for an effective treatment. Based on obvious advantages compared to conventional ICD systems, the question arises whether the S-ICD should actually be the first choice in the majority of all primary prevention patients in the future. Recent data from large registries show that S-ICD indications are also expanding in secondary prevention patients. As a consequence, the S-ICD was listed in the 2015 ESC guidelines as an alternative therapeutic option with a class-IIa recommendation in patients with an ICD indication not requiring pacing for bradycardia, cardiac resynchronization therapy or anti-tachycardia pacing (ATP). In addition, the American Heart Association guidelines refer to class-I recommendation for patients with a complex anatomy and venous access problems or at a high risk for infections who need ICD therapy. Limitations with respect to the not available pacing option of S-ICD might be also overcome by a potential combination with a leadless pacemaker in the near future. This article provides an overview of recent developments of S-ICD and reviews the most recent literature and ongoing studies.

Keywords: Efficacy; Evolution; S-ICD; Sudden cardiac death.

Fig. 1

The S-ICD provides three distinct sensing vectors for arrhythmia detection and discrimination: primary vector (from proximal electrode ring to can), secondary vector (from distal electrode ring to can) and alternate vector (from distal to proximal electrode).

Fig. 2

A: Sensing and detection of ventricular fibrillation (VF) treated by appropriate S-ICD shock therapy. First C denote capacitor charging, second C denotes end of capacitor charging. S = Sensing T = Tachycardia P = Post-Shock-Pacing. A dot indicates sensing of an unclassifiable event that is discarded. B. Demonstrating oversensing of P and T waves resulting in an inappropriate shock therapy.