In five European academic clinical centers, 700 ICD patients are prospectively enrolled (optionally the number of enrolled patients may be expanded to 1000 patients). Comprehensive non-invasive risk stratifying ECG diagnostics including beat-to-beat variability of repolarization (BVR) are applied, and candidate genes associated with malignant arrhythmias are analyzed. Programmed electrical stimulation is performed to test for inducibility of malignant ventricular arrhythmias and BVR. In a subset of patients, electrophysiologic studies include recording of monophasic action potentials (MAP) from the right ventricle for assessment of restitution properties. Non-invasive risk stratifying ECG methods are repeated annually. Outcome (mortality, ICD shocks) will be assessed until September 2014.