Subcutaneous implantable defibrillator: State-of-the art 2013

The subcutaneous implantable cardioverter-defibrillator (S-ICD) has recently been approved for commercial use in Europe, New Zealand and the United States. It is comprised of a pulse generator, placed subcutaneously in a left lateral position, and a parasternal subcutaneous lead-electrode with two sensing electrodes separated by a shocking coil. Being an entirely subcutaneous system it avoids important periprocedural and long-term complications associated with transvenous implantable cardioverter-defibrillator (TV-ICD) systems as well as the need for fluoroscopy during implant surgery. Suitable candidates include pediatric patients with congenital heart disease that limits intracavitary lead placements, those with obstructed venous access, chronic indwelling catheters or high infection risk, as well as young patients with electrical heart disease (e.g., Brugada Syndrome, long QT syndrome, and hypertrophic cardiomyopathy). Nevertheless, given the absence of intracavitary leads, the S-ICD is unable to offer pacing (apart from short-term post-shock pacing). It is therefore not suitable in patients with an indication for antibradycardia pacing or cardiac resynchronization therapy, or with a history of repetitive monomorphic ventricular tachycardia that would benefit from antitachycardia pacing. Current data from initial clinical studies and post-commercialization "real-life" case series, including over 700 patients, have so far been promising and shown that the S-ICD successfully converts induced and spontaneous ventricular tachycardia/ventricular fibrillation episodes with associated complication and inappropriate shock rates similar to that of TV-ICDs. Furthermore, by using far-field electrograms better tachyarrhythmia discrimination when compared to TV-ICDs has been reported. Future results from ongoing clinical studies will determine the S-ICD system's long-term performance, and better define suitable patient profiles.