A project of the feasibility of using NightOwl to detect the prevalence of obstructive sleep apnea (OSA) in patients with atrial fibrillation (AF). The long-term aim is to use the device to screen for OSA in a randomized clinical trial in AF patients undergoing ablation and/or a randomized trial of AF patients undergoing cardioversion.

Patients diagnosed with any type of AF referred to anticoagulation initiation at a nurse-run ambulatory will beasked to participate. The ambulatory consists of four daily nurse-led tracks at Department ofCardiology, Herlev-Gentofte University Hospital. In a formal collaboration, Department ofPulmonology, Herlev-Gentofte University Hospital provides work-up with cardio-respiratory monitoring investigation and clinical evaluation of initiating treatment of sleep apnea in patients referred from the study. ParticipantsParticipants with AF, without known sleep apnea, and indication for anticoagulation will be recruited from the Thrombosis unit (Tromboseklinikken) at Herlev-GentofteHospital. Participants will be contacted and asked of participation in the research project by a local investigator or a project nurse as part of their standard check at the anticoagulation outpatient clinic at Herlev and Gentofte Hospital. The conversation will include verbal participant information about the research project and about the right of time to consider recruitment. The written participant information will be handed to the participants prior to the verbal information, and it will be handed to the participants by a researcher with thorough knowledge to the project or a project nurse. The information needed for finding qualified participants, before a written informed consent is obtained, will be passed on to the investigators. The written informed consent allows the researchers to obtain necessary information for the project in the participant's medical health records

Study Design:

The is a cross sectional study. In total two visits will be planned, with a third visit for the first 20 participants and participants with apnea-hypopnea index (AHI)>15 included in the study.

1. Initial visit with time for clinical evaluation, questionnaire of OSA symptoms, theparticipant borrows a NightOwl and receive device instructions.
2. Four night of recording with NightOwl™ in home environment.
3. Follow-up visit for the home-monitoring results and soft node questionnaire.
4. For the 20 first patients and for all patients where the home test is showing (AHI>15) a fourth visit at the sleep apnea clinic will be arranged.

The time plan for the study inclusion until last patient enrolled are estimated to be approximately 6months

Inclusion Criteria:

1. Diagnosis of AF of any type
2. Age < 90 years
3. Age >18 years

Exclusion Criteria:

1. Known sleep apnea
2. Secondary AF (post-surgical, due to infection, thyroid-induced)
3. Known or newly discovered severe ventricular ectopic beats (as defined by the NightOwl manual)
4. Professional drivers
5. Severe heart failure (New York Heart Association class III or IV)
6. Severe chronic obstructive pulmonary disease (use of home oxygen)

Patients diagnosed with AF referred to anticoagulation initiation at a nurse-run ambulatory will be asked to participate.

Participants will be recruited from the Thrombosis unit (Tromboseklinikken) at Herlev-Gentofte Hospital. Patient reporting of symptoms for sleep apnea is not included as inclusion or exclusion criteria.