This study will test the hypothesis that implantation of a subcutaneous implantable cardioverter defibrillator (S-ICD) without performing a defibrillation test is non-inferior to S-ICD implant with a defibrillation test with regards to the primary endpoint failed first shock in a spontaneous arrhythmia episode when implant position is confirmed with PRAETORIAN score.

Implantable Cardioverter Defibrillator (ICD) implant improves survival in patients with a higher risk for sudden cardiac death. There are 2 types of ICD available; transvenous ICD (TV-ICD) and subcutaneous ICD (S-ICD). During ICD implant, defibrillation testing (DFT) is performed to test functionality of the device. However, DFT can be associated with complications such as inability to convert, complications arising from general anaesthesia, prolonged resuscitation, stroke and death. Whereas DFT may be associated with complications, the benefit of DFT is debated as literature shows there is only a modest average effect of DFT, if any, on mortality, shock efficacy or safety. Recently it was shown in a randomized controlled trial called 'SIMPLE' that routine defibrillation testing of TV-ICDs at the time of implant does not improve shock efficacy or reduce arrhythmic death. For S-ICD there is only limited data available of the effect of DFT on S-ICD efficacy. Data have however shown that the conversion efficacy of the S-ICD is comparable to TV-ICD.

DFT is currently performed in standard S-ICD implants, but is omitted in specific cases. However, an alternative method to evaluate the correct position may be desired when omitting DFT. The PRAETORIAN Score is developed using computer modelling data on factors influencing defibrillation thresholds. The PRAETORIAN score represents the chance of a patient having an elevated defibrillation threshold and consequently failing a DFT or conversion of a spontaneous arrhythmia episode. The score was retrospectively validated in two studies with 180 and 321 patients.

It was reported that most S-ICD implants are performed under general anesthesia, however other anesthesia protocols are used as well. One of the most predominant factors to use general anesthesia is the performance of the DFT. If this is omitted, other anesthesia protocols may be a good option for many patients as well.

Inclusion Criteria:

• Patients who meet current guidelines for ICD therapy and intent to undergo a de novo implant procedure for an S-ICD
• Patients must pass S-ICD screening per local routine
• Patients over 18 years of age, willing and capable to give informed consent
• Patients must be willing and capable of complying to follow up visits
• Patient must be eligible for either DFT strategy per physician discretion

Exclusion Criteria:

• Patient with a life expectancy shorter than 12 months due to any medical condition
• Patients known to be pregnant
• Patients with intracardiac thrombus
• Patients with atrial fibrillation without appropriate anticoagulation
• Patients likely to undergo heart transplant within 12 months
• Patients with LVAD
• Patients with other contra-indications for DFT per physician's discretion