Shock Without Wires: A Look at Subcutaneous Implantable Cardioverter-Defibrillator Compared to Transvenous Implantable Cardioverter-Defibrillator for Ventricular Arrhythmias.

Sudden cardiac death is a major cause of cardiovascular mortality in the United States with 250,000-450,000 deaths annually. Transvenous Implantable Cardioverter-Defibrillator (ICD) has been conventionally used for both primary and secondary prevention of ventricular tachycardia or fibrillation (VT/VF). It is also associated with a high risk of complications like hemothorax, pneumothorax, cardiac tamponade, lead failure, and increased risk for infections. Subcutaneous ICD (S-ICD) poses as a viable alternative with reduced chances of complications. This manuscript aims to review S-ICD as an alternative to conventional transvenous ICD and its efficacy. We conducted a Medline search of "Subcutaneous," "ICD," "transvenous," and "ventricular tachycardia or fibrillation (VT/VF)" to identify pivotal trials published before June 2021, for inclusion in this review. Major practice guidelines, trial bibliographies, and pertinent reviews were examined to ensure the inclusion of relevant trials. The following section reviews data from pivotal trials to review the efficacy of S-ICD for the termination of VT/VF. The S- ICD system consists of a pulse generator positioned over the sixth rib between the midaxillary and anterior axillary line and a tripolar parasternal electrode with the proximal and distal sensing electrodes positioned adjacent to the xiphoid process and manubriosternal junction, respectively. The conversion of the efficacy of the S-ICD after the first shock ranges from 88%-90.1% and 98.2%-100% after 5 shocks based on the current evidence. The device also has a 99% complication-free rate at 180 days with no increased complications even in ESRD patients. The PRAETORIAN trial showed non-inferiority of the S-ICD to transvenous ICD concerning device-related complications or inappropriate shocks in patients. S-ICD has several advantages including no need for fluoroscopy for implantation, decreased risk of infections, complications, and evidence of safety even in high-risk populations like ESRD. The limitations include the inherent lack of pacing abnormalities, the increase in inappropriate shocks compared to transvenous ICD, and non-reliability if there are baseline T wave abnormalities, especially in the inferior leads. Thus, S-ICD can be considered as an alternative to transvenous ICD in patients with an indication for defibrillator therapy but with no indication for pacing.