Subcutaneous ICD

Subcutaneous ICD (Implantable Cardioverter Defibrillator)


Subcutaneous ICD (S-ICD) is the term used to designate ICDs which are purely subcutaneous, without any intracardiac leads. It was designed aiming to avoid the problems due to an intravascular lead for defibrillation, which is used in conventional ICD. An S-ICD uses a subcutaneous lead in the parasternal location and the defibrillation current passes between the lead and the active can implanted in the infra-axillary region. As there is no intracardiac lead, it has only facility for short period back up bradycardia pacing. Hence it cannot be used for those with indication for bradycardia pacing. Similarly, it cannot be used when combined cardiac resynchronization therapy (CRT) is needed (CRT-D). S-ICD has another disadvantage in that it cannot be used for terminating ventricular tachycardias by overdrive pacing.

Still, S-ICD can be considered in those with inherited channelopathies with propensity for life threatening ventricular arrhythmias, congenital heart diseases with limitations on lead placement due to poor venous access, in immunocompromised hosts who are more likely to have intravascular infection and in the young and active with higher chance of conventional ICD lead failure.

The device is much bulkier than conventional ICDs because higher defibrillation energy is needed for S-ICD. Battery life may also be lesser for the same reason.

Data on use of S-ICD pediatrics and congenital heart disease has been published by von Alvensleben JC et al [1]. It was an international multicenter, retrospective analysis through the Pediatric & Congenital Electrophysiology Society. Complications at 30 days and 360 days, inappropriate shocks and appropriate shocks were evaluated. There were 115 patients in the study with median follow up of 32 months. 55% were implanted for primary prevention. Complication rate at 30 days was 7.8% and 14.7% at 360 days. Inappropriate shocks were noted in 15.6% patients. Appropriate therapy was delivered in 11.2%. Acute first shock success was 92.5%.

Reference

  1. von Alvensleben JC, Dechert B, Bradley DJ, Fish FA, Moore JP, Pilcher TA, Escudero C, Ceresnak SR, Kwok SY, Balaji S, Aziz PF, Papagiannis J, Cortez D, Garnreiter J, Kean A, Schäfer M, Collins KK. Subcutaneous Implantable Cardioverter-Defibrillators in Pediatrics and Congenital Heart Disease: A Pediatric and Congenital Electrophysiology Society Multicenter Review. JACC Clin Electrophysiol. 2020 Dec;6(14):1752-1761.