Extravascular defibrillator in patients not suited for the subcutaneous defibrillator

Abstract Background The subcutaneous defibrillator (sICD) was developed to mitigate the risks associated with intravascular hardware(1). However, failure of the screening test may occur, and inappropriate shocks due to myopotential or T-wave oversensing may be recurrent and not correctable despite careful programming owing to the underlying heart disease or to peculiar EKG features causing a small R wave or an unfavorable R/T ratio for sICD detection. It is speculative that the extravascular defibrillator (EV ICD) represents an alternative to the sICD in this situations(2). Objective to evaluate the efficacy EV ICD implantation in patients who either fail the sICD screening or had recurrent inappropriate shocks due to oversensing that could not be corrected. Methods From November 2020 to May 2024, 10 patients with an indication for ICD, who either failed the S-ICD screening test or experienced non-correctable oversensing with inappropriate shocks with a previously implanted S-ICD, underwent EV ICD implantation. All patients underwent a thoracic CT scan to guide substernal lead placement(2-3). The device was placed in an intermuscular pocket between the latissimus dorsi and serratus anterior muscles at the left mid-axillary line(4). Defibrillation testing (DFT) was performed using a standardized protocol. Patients were monitored clinically and remotely along follow-up (FU). Results EV ICD implantation was successful in all 10 patients (4 females), 7 patients for primary prevention, with no complications. 8 patients failed the sICD screening, while 2 had their sICD turned off because of recurrent inappropriate shocks due to oversensing, 1 of these latter had also a lead failure being replaced formerly. These 2 patients had the sICD extracted during EV ICD implantation. The mean age, BMI, NYHA class, and left ventricular ejection fraction were 45±17 years, 23.3±4 kg/m², 1.3±0.5, and 50±12%, respectively. The underlying cardiac disease was non-ischemic cardiomyopathy (9/10), including 5 patients with arrhythmogenic cardiomyopathy, 2 with Brugada syndrome, and 1 with idiopathic VF. DFT was performed in all patients, successfully terminating induced VF with shocks of 15J in 5 patients, 20J in 4 patients, 30J in 1 patient (average 18.5J). The median sensing amplitude at implantation was 3.1±1.7 mV and remained stable at 3.4±1.9 mV over a FU period of 21±12 months. 1 Brugada patient with prior sICD oversesnig had a small R-wave ranging from 0.7 to 1.2mV both during implant and at FU, and was implanted based on the DFT (sensing better than during sinus rhythm). His clinical course has been uneventful along 18 months. The R1-R2 vector was chosen as the sensing configuration for all patients, and there were no inappropriate therapy delivery at FU. Conclusions The EV ICD is a clinically effective opportunity for patients who fail the screening test for the sICD, or with inappropriate sICD shocks refractory to corrective re-programming and interventions.