Validation of the "ApneaScan" Algorithm for the Detection of Sleep Disordered Breathing in Chronic Heart Failure

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