The COGENT-4 Field Following Study will evaluate the clinical performance of the Boston Scientific TELIGEN 100 HE Implantable Cardioverter Defibrillator (ICD), the COGNIS 100 HE Cardiac Resynchronization Therapy ICD (CRT-D) systems and the RELIANCE 4-SITE defibrillation lead (when available). An optional sub-study will also evaluate the clinical performance of the Reverse Mode Switch (RMS) feature in the TELIGEN 100 HE DR ICD.

Inclusion Criteria:

• ICD indication according to normal clinical practice (for those patients receiving a TELIGEN 100 HE)
• CRT-D indication according to normal clinical practice (for those patients receiving a COGNIS 100 HE)
• Willing and capable of providing informed consent, undergoing a device implant, participating in all testing associated with this clinical investigation at an approved clinical investigational centre and at the intervals defined by this protocol
• Geographically stable patients who are available for follow-up at a study centre
• Age 18 or above, or of legal age to give informed consent specific to national law

Exclusion Criteria:

• Documented life expectancy of less than six months or expected to undergo heart transplant within the next six months
• Patients currently requiring dialysis
• Women who are pregnant or plan to become pregnant. Method of assessment per physician discretion
• Enrolled in any concurrent study
• Patients implanted with the following leads which will not be abandoned:
• Atrial or right ventricular unipolar leads
• Patch defibrillation leads
• Non-compatible defibrillation leads (e.g. 5/6mm)

Patients with risk of developing life threatening ventricular arrhythmias with and without heart failure