The goal of this observational study is to investigate sex - differences in detection rate of atrial fibrillation after cryptogenic stroke (embolic stroke of unknown cause) - using an implantable cardiac rhythm monitor - and the treatment effects of oral anticoagulation on recurrent stroke, ischemic cardiovascular events, major bleeding risk, disability and mortality.

The main questions to answer are:

• Is long-term monitoring and detection of atrial fibrillation after stroke of unknown cause in women related to recurrent stroke and disability?
• Is long-term monitoring and initiation of oral anticoagulation related to cardiovascular events and intracranial haemorrhages? And in addition increased in women compared to men?
• Is long-term rhythm monitoring after stroke with unknown cause related to patient reported outcomes in women?

This is a prospective, observational, study including consecutive patiens with acute cryptogenic stroke /embolic stroke of unknown source (ESUS) or transient ischemic attack (TIA) admitted between 2016 and 2023 at Akershus University Hospital (AUH). As part of the standard investigation at AUH, selected patients are offered an implantable cardiac monitor (ICM) and followed up for detection of atrial fibrillation (AF) by a specialised neurocardiology team. A control group recruited at another hospital during the same period, Haukeland University Hospital (HUS), only comprise women.

The primary objectives:

• To investigate among women with stroke of unknown cause, the effect of implantable cardiac monitors compared to standard non-invasive approach on AF detection, recurrent stroke, death and disability.
• To investigate sex- differences in patients with stroke of unknown cause, the effect of implantable cardiac monitors on AF detection, recurrent stroke, death and disability.

Secondary objectives:

• To compare the rate of cardiovascular events and intracranial haemorrhages after stroke of unknown cause in women offered implantable cardiac monitors, compared to best standard non-invasive follow up
• To investigate the impact of implantable cardiac monitors on the use of oral anticoagulation in women
• To investigate self-perceived health and health related quality of life after stroke of unknown cause in women offered implantable loop recorders, compared to women offered best standard non-invasive approach to detect AF

Inclusion Criteria:

• Patients diagnosed with cryptogenic stroke or TIA, according to the TOAST (Trial of Org 10172 in Acute Stroke Treatment) classification and an implantable cardiac rythm monitor (ICM) for the ICM group not the control

Exclusion Criteria:

• Patients with known or newly detected AF on standard ECG or 24 h Holter ECG.
• Patients on oral anticoagulants (OAC) for non-AF indications
• Patients with strong contraindications for OAC
• Severe cognitive impairment or disability or with a short life expectancy due to comorbidities of less than two years.

In total 1050 patients. A cohort of at least 700 patients of both sexes diagnosed with acute cryptogenic stroke or TIA and with an implantable cardiac monitor, admitted to the stroke unit at Akershus University Hospital, Norway.

A control group of 350 women with acute cryptogenic stroke or TIA, with non-invasive standard monitoring, admitted to the stroke unit at Haukeland University Hospital.

Due to Norwegian regulations, the data cannot be shared publicly, and the authors are not permitted to share the data or study materials used in this study. De-identified datasets may be made available from the corresponding author upon reasonable request and with appropriate ethical and institutional approvals.