P1157
Defibrillation threshold with subcutaneous implantable-cardioverter defibrillator implanted using an intermuscular 2-incision approach

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Rhythm Detect Registry

Current subcutaneous implantable cardioverter–defibrillators (S-ICD) deliver 80J, and the conversion test is usually conducted by delivering shock energy of 65 J to ensure a safety defibrillation margin of at least 15 J. However, little is known about the real safety margin in real life clinical practice.

To determine the defibrillation threshold (DFT) with S-ICD and to investigate its association with clinical characteristics.

De novo S-ICD patients were  consecutively enrolled and DFT was evaluated using a pre-specified step-up protocol at implantation.

35 patients, BMI 25 ± 4 kg/m2, left ventricular ejection fraction (LVEF) 48 ± 19%, underwent S-ICD implantation. The generator was positioned in an intermuscular pocket and a 2-incision technique was applied in all patients. The mean DFT was 30 ± 10J and the DFT was >30J in 7 (20%) patients. A single patient had a >40J DFT. The time to shock was 11 ± 3 seconds and the shock impedance was 67 ±21 Ohm at the lowest effective energy. The DFT was comparable in patients with LVEF ≤35% (33 ± 15J) versus >35% (29 ± 5J, p = 0.278), and in patients with BMI ≤25 kg/m2 (30 ± 5J) versus >25kg/m2 (31 ± 14J, p = 0.864).

We observed low DFT and low shock impedance in patients who received S-ICD with an intermuscular 2-incision approach. The S-ICD defibrillation success rate at ≤30J was 80%, while 97% of patients were defibrillated at ≤ 40J. We found no difference in DFT according to the LVEF or the BMI.