Validation of the ApneaScan Algorithm in Sleep Disordered Breathing

72 patients with heart failure with reduced ejection fraction (HFREF) who have been selected to receive an Implantable Cardioverter-Defibrillator (ICD) or Cardiac Resynchronization Therapy Pacemaker or Defibrillator (CRT-P/D) will undergo pre-implant assessment with an echocardiogram, B-type Natriuretic Peptide (BNP) level, 6 minute walk test, Minnesota living with heart failure and Epworth sleepiness questionnaires. The patients will then have the device implanted. 6 to 8 weeks later the patent will undergo an Embletta home sleep study and download of the ApneaScan data from the device. The mean Apnoea-Hypopnoea Index (AHI) from the ApneaScan download will be compared with that derived from the sleep study. The patients will also have a repeat 6 minute walk test, echocardiogram and BNP level. 2 years after device implantation, all patients will be followed up to document deaths, hospital admissions, Atrial Fibrillation (AF) burden and appropriate therapies from ICD devices.