Clinical Status Monitoring in Implantable Cardiac Defibrillator (ICD) Patients by Physiological Diagnosis (PhD) Function

Inclusion Criteria: 1. Patient eligible for implantation of an ICD or a CRT-D device according to current available guidelines. 2. Documented chronic HF (NYHA Class II to IV) at the time of enrollment 3. Scheduled for implant of a PARADYM ICD / CRT-D or implanted within the previous month 4. Signed and dated informed consent Exclusion Criteria: 1. Any contraindication for ICD therapy 2. Abdominal implantation site 3. Acute myocarditis 4. Unstable coronary symptoms (unstable angina or myocardial infarction) within the last month 5. Planned heart transplant 6. Mechanical tricuspid valve 7. Unable to perform the 6 minute Walking Test at time of enrollment 8. Already included in another clinical study 9. Life expectancy less than 13 months 10. Inability to understand the purpose of the study or refusal to cooperate 11. Inability or refusal to provide informed consent 12. Under guardianship 13. Age of less than 18 years 14. Pregnancy (Women of childbearing potential should have a negative pregnancy test prior to enrollment)