The goal of this observational study is to follow all patients implanted with extravascular implantable cardioverter-defibrillators (EV-ICDs) in Belgium throughout the lifetime of the devices. The main goal of the study is to keep track of:

• all parameters of the device
• complications
• arrhythmia detection and therapy delivery
• clinical endpoints (quality of life, cardiac and infectious events) Participants who underwent or will undergo an EV-ICD implantation as part of their regular medical care will be asked if data can be collected from their medical record. No additional tasks are required for the study.

The BELIEVE registry (BELgian registry of Implanted EV-ICDs to Evaluate parameters and complications) is a multicenter, observational registry designed to gather real-world data on the use of extravascular implantable cardioverter-defibrillators (EV-ICDs) in Belgium. This new generation of ICD technology offers the potential advantages of both subcutaneous (S-ICD) and transvenous (TV-ICD) devices, with the lead placed under the sternum. This position enables pacing capabilities and more accurate arrhythmia detection while aiming to minimize lead-related complications seen in previous ICD systems.

Given the relatively recent introduction of EV-ICDs, it is essential to monitor their performance and clinical outcomes in routine clinical settings. While initial trials have demonstrated feasibility and safety, real-world data are crucial for understanding long-term efficacy, complication rates, therapy effectiveness, device longevity, and overall patient outcomes. The BELIEVE registry was therefore established to support this need, offering a structured framework to follow patients over time and improve clinical practice related to EV-ICDs.

The registry is both retrospective and prospective, non-randomized, and will include all patients in Belgium who undergo (or have undergone) an EV-ICD implantation-regardless of whether the procedure was successful. Participating centers will aim to enroll an initial cohort of 100 patients over a 4-year period, although the number of patients and study duration may be extended. The total planned study period is 15 years, with patients followed throughout the life of their device.

Inclusion criteria are broad: participants must be at least 18 years old, have had or be scheduled for an EV-ICD implantation (even if unsuccessful), and must provide informed consent. Patients who did not undergo any part of the implantation procedure are excluded.

Data will be collected at baseline, during the procedure, and during scheduled follow-up visits (at 1-3 months, 6 months, and then at least annually). Information will include demographic and clinical characteristics, medical history, device data, arrhythmia detection, therapy delivery, programming changes, complications, and patient-reported outcomes.

Inclusion Criteria:

• At least 18 years old
• Previous or planned EV-ICD implantation (successful or not)
• Informed consent signed

Exclusion Criteria:

• Patients who did not undergo any step of the implantation procedure

All patients who underwent or will undergo an EV-ICD implantation in Belgium, whether successful or not, can be included in this registry.