Introduction
The optimal duration and timing of cardiac rhythm monitoring after cryptogenic stroke is unknown. Identification of reliable biomarkers indicating AF will be valuable in the selection of patients for prolonged cardiac rhythm monitoring. The purpose of the study is to assess the incidence of AF detection using insertable cardiac monitors (ICMs) (Reveal LINQ®) in patients with cryptogenic stroke or TIA and to identify biomarkers that can be used as predictors of incident AF. In our pilot study we searched for multiple biomarkers that can potentially be used as predictors of incident AF in patients with ischemic stroke or TIA in a population with known stroke etiology.

Methods
Our study is a multi-center prospective observational study of the occurrence of AF in cryptogenic stroke / TIA patients with implantable cardiac monitors for 12 months. Blood samples measuring biomarkers are taken in the acute phase and at 12 months´ follow-up. Estimated number of patients to be included in the study is 500. In the pilot study blood samples from 3 groups of participants were taken and analyzed with the Olink technology and further biostatistics by Gene set enrichment analysis. 

Results
By October 2018, the total number of patients included in 13 out of 19 participating centres is 115. Out of 115 included patients, AF or atrial flutter has been detected in 26 patients, resulting in detection rate of 22,6 %. The pilot study has identified multiple biomarkers that seem to be useful for the detection of AF in cryptogenic stroke / TIA such as GDF-15, IL16, ITGB2, vWF, CEACAM8, PTX3, TGM2, CD163, U-PAR, IL-27, and MERTK. 

Conclusion
ICMs are effective in detecting AF in patients with cryptogenic stroke. There are multiple proteins that may potentially be used as biomarkers for the detection of AF in cryptogenic stroke / TIA patients. However, studies with larger samples are needed. In the on-going NOR-FIB study we plan further biomarker assessment in patients with cryptogenic stroke / TIA undergoing long-term cardiac rhythm monitoring with ICM.

Atrial fibrillation in cryptogenic stroke The Nordic Atrial Fibrillation and Stroke Study (NOR-FIB)