A prospective observational multi-centre study for the validation of the ApneaScan algorithm (integrated in ICD devices (with or without cardiac resynchronization therapy function) of the "Incepta" series for the screening of sleep disordered breathing in patients with stable symptomatic chronic heart failure, using portable polygraphy monitoring device ("Embletta Gold") as reference for the Apnea-Hypopnea-Index (AHI).

Secondary objectives are the detection of severe sleep disordered breathing in patients with clinically indicated in-laboratory polysomnography, as well as correlations of the AHI detected by ApneaScan with other clinical endpoints like mortality, hospitalization, atrial fibrillation and ventricular arrhythmia.

Inclusion Criteria:

• Age over 18 years
• Patient´s written informed consent
• Patients with a cardiac rhythm management device (ICD with or without cardiac resynchronization therapy function) of the "Incepta" series (including the ApneaScan algorithm) already implanted for at least 8 weeks (corresponding to the duration of the leads´ healing process); in order to standardize the enrollment period, inclusion should be effected between the first (the earliest 8 weeks after implantation) and the second routine control of ICD-function (the latest 9 months after implantation)
• Stable symptomatic chronic heart failure for either ischemic or non-ischemic reason (moderately to severely impaired systolic left ventricular function with NYHA-class II to III) under optimal pharmacological treatment (according to guidelines 2012 of the European Society of Cardiology)

Exclusion Criteria:

• Unstable heart failure (NYHA-class IV) or asymptomatic chronic heart failure (including patients with very mild exercise induced dyspnea, i.e. NYHA-class I)
• Patients already treated for sleep apnea syndrome (i.e. continuous positive airway pressure mask) or chronic obstructive pulmonary disease with GOLD-class IV (i.e. long-term oxygen therapy)
• A limited AHI detection by the ApneaScan algorithm until the planned inclusion (randomly defined by <50% of countable AHI detection-points within the last 2 weeks).
• Patients with limited mobility due to orthopedic, neurologic or oncologic diseases (because of restricted assessment of exercise induced dyspnea)
• Patients on dialysis (either acute or chronic)
• Alcoholism or regular intake of hypnotics
• Pregnancy and lactation

Patients with stable symptomatic chronic heart failure and implanted ICD/CRT-D of the "INCEPTA" series