Utility and feasibility of intra-pocket mapping technique for optimal subcutaneous implantable cardioverter...

A subcutaneous implantable cardioverter defibrillator (S-ICD) is an alternative to a conventional transvenous implantable cardioverter defibrillator for preventing sudden cardiac death. Although posterior chest S-ICD implantation has been recommended for better defibrillation outcomes, little is known about the optimal S-ICD positioning for R-wave detection. Herein, we report two cases of S-ICD recipients in whom antero-inferior chest positioning improved R-wave detection after posterior chest positioning failed.

Two patients experienced intraoperative S-ICD sensing test failures despite passing the preoperative screening. The first case was a 66-year-old man with arrhythmogenic right ventricular cardiomyopathy and superior vena cava syndrome due to transvenous leads. After lead extraction and initial S-ICD placement in the posterior of the mid-chest line, sensing tests failed in all vectors. We performed intra-pocket mapping and repositioning to the antero-inferior chest position, which enabled R-wave detection and a successful defibrillation threshold test. The second case involved a 34-year-old man with short QT syndrome, whose intraoperative sensing tests also failed in all vectors. Antero-inferior repositioning of the S-ICD generator achieved acceptable R-wave detection without T-wave over-sensing and defibrillation threshold test failure.

These cases highlight the utility of intra-pocket mapping to optimize S-ICD positioning for R-wave detection in patients with challenging electrocardiogram characteristics. Posterior chest positioning may not be optimal for R-wave detection, particularly in patients with low R-wave and/or high T-wave amplitudes. Repositioning the device closer to the left ventricular apex improved sensing test results, supporting antero-inferior chest placement as a potential solution when posterior chest placement fails.