Successful Defibrillation Verification in Subcutaneous Implantable Cardioverter-Defibrillator recipients by Low-Energy Shocks.

BACKGROUND: The S-ICD is an effective alternative to the transvenous one. Defibrillation efficacy depends on maximum device output and on the optimal device location at device implantation. Little is known about the real safety margin in real life clinical practice.

METHODS: We sought to understand what is the efficacy of induced VF termination at S-ICD implantation using lower energies than the recommended 65J.

RESULTS: 64 consecutive S-ICD recipients underwent VF termination attempts at implantation with energies ranging from 20 to 50 J. Overall, VF termination occurred in 84% of patients with ≤40J , in 88% with 45J , and in 100% with 60 J. Intermuscular S-ICD placement was associated with 94% VF termination at ≤40J. A ejection fraction <35% was associated to higher energy requirement for defibrillation, however an intermuscular S-ICD placement conferred 90% defibrillation efficacy at 31±5J in this patients subset.

CONCLUSIONS: This is a hypothesis-generating observation that prompts a methodologically correct investigation to prove that a 60J output S-ICD can provide an adequate safety margin to terminate VF in clinical practice. This would enable superior device longevity and/or device downsizing for pediatric/small size patients.