Introduction: Subcutaneous implantable cardio-defibrillators (S-ICDs) can either be implanted in a pocket between latissimus dorsi and serratus anterior muscles or behind the serratus anterior muscle. Both techniques are used by operators at our centre. We performed a retrospective, observational study of outcomes including complications, patient discomfort, aesthetics and device circuit shock impedance to see if any differences were observed between the two techniques.
Methods: All patients undergoing S-ICD implantation at Imperial College Healthcare from January 2017 to April 2019 were included in the study. Retrospective data was collected on implant technique, device complications and circuit shock impedance measurements using the local EP database. Patients were telephoned and asked to score from 0–10: a) pain immediately post implant, b) current discomfort levels from the device, c) current limitations to movement related to the device and d) how prominent the patient feels the device is. These were assessed at a single time point in all patients.
Results: Fifty-seven patients underwent S-ICD implantation at Imperial College Healthcare from 2017 to 2019; 35 patients had their device implanted between latissimus dorsi and serratus (group one) and 22 had their device implanted behind serratus (group two). Average time since implant was 15.2 ± 8.7 months. Average shock impedance was significantly lower in group two than in group one (58.3 ± 10.1 Ohms versus 70.0 ± 23.5 Ohms, p = 0.036). No significant difference in complication rates were seen between the two groups (four in group one versus 1 in group two, p=0.41). There was one device explant due to infection, one device reposition at two years for lead displacement and two cases with inappropriate shocks in group one, and one device reposition at patient request in group two. A non-significant increase in pain scores immediately post procedure was seen in group two (7.6 ± 1.6 in group one versus 8.4 ± 1.5 in group two, p=0.09), however there was no difference in current pain levels (1.0 ± 1.3 versus 1.3 ± 1.0), movement limitations (1.5 ± 1.9 versus 1.5 ± 2.3), or device prominence (1.0 ± 1.9 versus 0.7 ± 1.5) seen between the two groups (group one versus group two respectively).
Conclusion: Sub-serratus S-ICD implants had significantly lower shock circuit impedance values compared to S-ICDs implanted between latissimus dorsi and serratus. This may be beneficial for improved shock efficiency. No significant differences were noted in patient reported outcomes or complications rates between the two implant techniques, however there was a tendency to increased patient discomfort in the immediate post-op period in sub-serratus implants. These findings should be tested in a larger, prospective randomised controlled trial for confirmation.