The "EUropean Comparative Effectiveness Research to assess the use of primary prophylacTic Implantable Cardioverter Defibrillators (EU-CERT-ICD)" is a modular research project to study the effectiveness of prophylactic ICDs in a prospective study, a retrospective registry, and meta-analyses of existing evidence on the subject.

The prospective study part is an observational, prospective multi-centre study which aims to enrol 2500 patients with ischemic or dilated cardiomyopathy and primary prophylactic ICD indication for reduced left ventricular ejection fraction (LVEF) according to current guidelines. According to the treating physician's decision and preference which is independent from study participation, patients are recruited into one of two groups: patients directly prior to first ICD implantation (ICD Group), or patients who are not considered for prophylactic ICD treatment by the physician or are considered but refuse ICD treatment (Control Group). Patients will undergo simple 12-lead electrocardiogram (ECG) and Holter ECG diagnostics at baseline as well as genetic biobanking at entry to the study. All patients will be subsequently followed for at least 1 year and up to 4 years. Co-primary endpoints are all-cause mortality and appropriate ICD shocks.

Inclusion Criteria:

• Ischemic or dilated cardiomyopathy and recommendation for primary prophylactic ICD treatment following current international treatment guidelines
• Written informed consent
• If ICD implantation is planned, enrollment and study baseline testing needs to be completed before de-novo ICD implantation

Exclusion Criteria:

• Permanent atrial fibrillation or atrial fibrillation at baseline in case more than 15% of such patients at a given time have been enrolled
• Indication for secondary prophylactic ICD treatment
• Indication or candidate for cardiac resynchronization therapy
• AV block II°-III° at resting heart rates
• Implanted pacemaker
• Unstable cardiac disease such as decompensated heart failure (NYHA functional class IV) or acute coronary syndrome
• Participation in other clinical trials which exclude enrolment in other trials

Patients who are eligible for primary prophylactic ICD implantation and potentially eligible for study participation will be identified based on echocardiographic and/or 12 lead ECG results. For ICD Group patients, screening will be shortly before scheduled ICD implantation. For Control Group patients, the time span between primary diagnosis of eligibility for primary ICD implantation and the date of the primary diagnosis of cardiomyopathy must be recorded in the eCRF, together with how and when the decision not to prescribe a defibrillator was reached. Control group will be recruited from patients with ischemic or dilated cardiomyopathies and LVEF ≤ 35%. Patients scheduled for ICD implantation (ICD Group) undergo screening and baseline assessments prior to ICD implantation. Patients for the Control Group will undergo baseline assessments as soon as possible after screening. Baseline assessments are identical for the ICD Group and the Control Group.