Intermuscular placement and defibrillation with the extravascular ICD: a single-centre experience

Abstract

Abstract Background Extravascular (EV) implantable cardiac defibrillators (ICD) with substernal lead have recently proved to be a safe and effective alternative to conventional transvenous (TV) and subcutaneous defibrillators (S-ICD), owing to the possibility to deliver antitachycardia and asystole pacing while saving intravascular hardware. The proposed implantation technique for EV-ICDs is a subcutaneous pocket along the mid axillary line, although an intermuscular ICD placement can potentially reduce the risk of pocket complications, device migration and improve patient comfort and aesthetic outcomes. Purpose exploring the safety and feasibility of extravascular ICDs implantation with a substernal coil and an intermuscular generator placement. Methods Seventeen patients with a class I or IIa ICD indication either for primary (14/17) or secondary (3/17) prevention underwent EV-ICD implantation in our centre as part of the EV ICD Pivotal Study from May 2021 to November 2022. Access and tunnelling along the retrosternal space were performed based on current standard recommendations for EV-ICDs implantation. An intermuscular pocket for generator placement was obtained between the latissimus dorsi and the serratus anterior muscles beyond the left mid-axillary line. Results Mean age, BMI, NYHA class and left ventricular ejection fraction (LVEF) were respectively 53±9yrs, 25.3 ±6 kg/m2, 2 ±0.7, and 39±14%. The main aetiology was non ischemic cardiomyopathy (12/17), including 3 arrhythmogenic cardiomyopathy patients and one with hypertrophic cardiomyopathy. The implantation was successful in 16 (6 females) out of 17 patients, with one implant failure due to inadequate sensing (0,5 mV); the median sensing amplitude was 2,3 mV (min = 1,3 mV; max = 5,8 mV), with R1R2 being the final sensing vector chosen for 14/16 and R2-Can for 2/16. Defibrillation Testing (DFT) was performed in all patients: a 15 J shock terminated induced ventricular fibrillation (VF) in 12/16 patients, 20 J terminated VF in 3, a single patient had VF terminated at 30 J. No patient had infection or skin erosion or complained pain/discomfort at the pocket site along an 18±4 months follow-up. Only 1/16 patients had ventricular tachycardia at follow-up, successfully treated by the device. Conclusions Intermuscular placement of the EV ICD may be a feasible and reliable alternative to a subcutaneous one in terms of defibrillation efficacy, enabling patient comfort and aesthetic acceptance in thin-habit or young patients. Additional long-term data and larger patient cohorts are required to confirm its advantage compared to the subcutaneous placement.