Subcutaneous implantable cardioverter-defibrillator (S-ICD) for secondary prevention of sudden cardiac death.

Abstract

Implantation of a transvenous implantable cardioverter-defibrillator (ICD) is a recognized method of secondary prevention of sudden cardiac death [1]. In some patients with indications for such a device, circumstances may occur that render ICD implantation difficult or impossible. Implantation of a subcutaneous ICD (S-ICD), not requiring introduction of any elements into the cardiovascular system, might be a solution in such cases. Another feature that distinguishes the S-ICD from the ICD is the inability to terminate arrhythmias with antitachycardia pacing, but only with an electrical 80 J shock. Moreover, bradycardia pacing is limited only to the immediate post-shock period (50 bpm for 30 s). The S-ICD system consists of a 145 g can, placed subcutaneously over the 5th and 6th left intercostal space in the midaxillary line, and the lead, also placed in the subcutaneous tissue, along the left margin of the sternum. The battery life is approximately 5 years [2]. If correctly implanted, the device provides detection of ventricular arrhythmias with a sensitivity of nearly 100% and specificity of differentiation from supraventricular arrhythmias of 98%, which is more than in traditional transvenous systems [3]. Possible problems include sensing disturbances due to the oversensing of T-waves or myopotentials, which may lead to inadequate interventions. That problem may affect 5% to 16% of patients [4–6]. Due to that fact, S-ICD implantation is indicated only in patients with a positive screening test result, aimed to assess the amplitude and relation of R and T waves. Until recently, defibrillators of such kind had not been implanted in Poland. The reported case is one of the two first implantations in Poland.