PROACTIA is a prospective, event-driven observational study. It aims to propose a composite scoring system in order to evaluate the risk of paroxysmal atrial fibrillation (PAF) in patients after acute cryptogenic stroke and transient ischemic attack (TIA).

It will be enrolled 250 participants of both sexes within two weeks after diagnosed cryptogenic stroke and/or TIA at Akershus University Hospital, Oslo area, Norway.

Evaluation of participants' comorbidity with CHADS2-VASc score, ECG, Holter ECG, echocardiography, detection of biochemical cardiac markers and screening for obstructive sleep apnea syndrome will be performed. All participants will be monitored with a continuous cardiac rhythm during one year by implantation of implantable cardiac rhythm monitors (ICRM). All patients without high bleeding risk will get prescribed oral anticoagulants (OAC) after detection of PAF.

A biobank will be established in order to store the sampled biological material.

Inclusion Criteria:

- Patients diagnosed with cryptogenic stroke and/or TIA, in accordance to the TOAST (Trial of Org 10172 in Acute Stroke Treatment) classification.

Exclusion Criteria:

• Patients with known or newly detected AF on initial examination including 24 h Holter ECG.
• Patients on oral anticoagulants (OAC) for non-AF indications.
• Patients with strong contraindications for OAC, even if the presence of underlying AF is detected.
• Patients with atrial- or ventricular thrombi, or atheromas of the aortic arch greater than 4 mm, detected by transesophageal echocardiography.
• Patients unable to sign the informed consent or with a life expectancy due to comorbidities of less than two years.

250 participants of both sexes included at Akershus University Hospital, Norway, within two weeks after diagnosed with cryptogenic stroke and/or TIA.