The goal of this clinical trial is to compare the use of long-term vs. shorter-term heart monitoring to detect atrial fibrillation after stroke.

Patients will be implanted with a loop recorder and will have study follow-up at 3-, 6- an 12-months after implantation.

The investigators will evaluate 24 patients, between the 3 centers, in the same way the investigators plan to evaluate a larger number of participants (>1000) in a future study. This will allow us to learn if such a study is possible, identify potential implementation challenges, and develop strategies to overcome those difficulties.

Atrial fibrillation (AF) is the most common heart rhythm disorder. Its name comes from the fibrillation (i.e. quivering) of the two upper chambers (atria) of the heart instead of a coordinated contraction, causing a rapid, irregular heart rate. This irregular contraction is ineffective, leading to the development clots in the heart. These clots can travel through the bloodstream until they get stuck in a brain artery. Millions of brain cells that depend on the oxygen supplied by the blocked artery die within minutes. This is known as a stroke. Strong blood thinners known as anticoagulants can lower stroke risk by 64% in AF patients when the AF is detected on an electrocardiogram (ECG) or if it lasts more than 24h on a heart monitor. Therefore, doctors use cardiac monitors to record the heartbeats of stroke patients for up to 3 years. It was historically thought, but not proven, that if AF was found in stroke patients, using anticoagulants could prevent a second stroke. However, recent information suggests that using cardiac monitors in stroke patients increases AF detection and anticoagulants prescription without a reduction in the number of new strokes. The failure to prevent a second stroke is likely the consequence of cardiac monitors sometimes detecting very short-duration AFs, which may have a low risk of stroke. If AFs last only for a few minutes or hours, anticoagulants may not be needed.

Patients with a stroke and not know atrial fibrillation will be implanted with a loop recorder and randomized in two groups (disclosure arm and non-disclosure arm). Patients will have phone follow-up visits at 3, 6 and 12 months after implantation. A quality-of-life survey will be performed at the last study visit.

This study will assess if it is possible to organize a large clinical trial comparing the use of long-term vs. shorter-term heart monitoring. The investigators will evaluate 24 patients, between the 3 centers, in the same way, the investigators plan to evaluate a larger number of participants (>1000) in a future study. This will allow us to learn if such a study is possible, identify potential implementation challenges, and develop strategies to overcome those difficulties.

Inclusion Criteria:

- Adult patients with cortical or subcortical, cryptogenic or non-cryptogenic acute ischemic stroke

Exclusion Criteria:

• AF on 24-h inpatient or Holter monitoring
• Atrial or ventricular thrombus
• Other major-risk cardioembolic sources (e.g., mechanical valve)
• Other indications (e.g., venous thromboembolism) or contraindications for OACs.