The overall objective of the DISCERN study is to develop and validate a genomic diagnostic assay to identify patients at increased risk for lethal ventricular arrhythmias and sudden cardiac death (SCD).

This is a prospective, multi-center, observational study. The research will be performed in three phases, each using distinct patient cohorts:

Phase I: Discovery - genes/biomarkers/clinical factors Phase II: Algorithm Development Phase III: Assay Validation

The final algorithm (Assay) may incorporate a combination of factors including genetic markers, biomarker(s), and clinical factor(s). Participation in the study does not alter clinical care. The procedures required by the protocol are collection of a research blood sample (at baseline only) and interviews with the subject to collect specific clinical information at baseline and follow-up (6 mos, 1 yr, 2 yr, 3 yr, 4 yr, and 5 yr) after enrollment. All other data collected is in accordance with the participating institution's standard patient care.

Inclusion Criteria:

• Implantable cardiac defibrilIator (ICD) or cardiac resynchronization therapy defibrillator (CRT-D) implanted for primary prevention
• Left ventricular ejection fraction (LVEF) ≤ 50 %
• Ability to collect clinical follow-up and endpoint information, including device interrogation data

Exclusion Criteria:

• Congenital heart disease
• Known inherited arrhythmia disorder
• Organ transplantation
• Inability to give informed consent

Patient's with ventricular dysfunction (low ejection fraction) undergoing implantation of ICD or CRT-D for primary prevention. Patient's may be enrolled at time of implant or during follow-up in electrophysiology clinic as long as full device records are available since time of implant.