Each year, 7.8 million people worldwide experience an ischemic stroke, often caused by atrial fibrillation (AF). AF is a major contributor to severe, disabling, and deadly strokes. About 20% to 30% of ischemic stroke patients have AF before their stroke. Of the remaining 70% to 80% without known arrhythmias, up to 24% are newly diagnosed with AF after intensive cardiac monitoring, totaling 1.3 to 1.5 million new AF cases detected after stroke globally each year. Oral anticoagulants (OACs) can reduce stroke risk related to AF by 64% and lead to milder strokes with lower disability and mortality. Neurologists use cardiac monitoring to detect AF in stroke patients.

This study focuses on patients who have had an ischemic stroke and are newly diagnosed with AF. The goal is to understand how AF progresses over time. The investigators will track changes in AF severity and frequency, monitor biomarkers related to heart health, assess the size and function of the left atrium, and observe new risk factors like hypertension. Patients will be grouped based on their AF diagnosis method: ECG, a portable device recording heart activity for less than 7 days, or one recording for 7 to 30 days.

The investigators hypothesize that AF burden will increase, new risk factors will emerge, biomarkers will rise, and the left atrium will worsen over time. Participants will be followed for up to 24 months with regular assessments. The study aims to provide insights into AF progression in stroke patients, potentially improving treatments and prevention strategies.

Globally, 7.8 million individuals experience an ischemic stroke each year.1, 2 Atrial fibrillation (AF) is one of the most frequent causes of ischemic stroke, resulting in the most severe, disabling, and lethal events.1, 2 Around 20% to 30% of ischemic stroke patients have AF before stroke occurrence.13, 14 Among the remaining 70% to 80% without known arrhythmias, up to 24% can be newly diagnosed with AF after intensive cardiac monitoring (Figure 1), yielding a rough estimate of 1.3 to 1.5 million new cases of AF detected after stroke (AFDAS) globally each year.15-17 Most AFs are diagnosed before a stroke ever occurs. Among persons with additional stroke risk factor, OACs reduce AF-related stroke risk by 64% compared to no treatment.18 Also, patients who have ischemic strokes despite receiving OACs have milder19 and smaller strokes20, resulting in reduced disability21 and mortality21. Neurologists use cardiac monitoring in patients with ischemic stroke to look for AF.

The main goal of this study is to observe and understand how AF progresses over time in patients with AFDAS. Specifically, the investigators aim to track changes in the severity and frequency of AF episodes, monitor biomarkers (substances in the blood that indicate disease) related to heart health, measure changes in the size and function of the left atrium (a chamber of the heart), and analyze changes in risk factors such as new diagnoses of hypertension (high blood pressure). Patients will be grouped based on how their AF was diagnosed: using an electrocardiogram (ECG-based diagnosis), using a portable device that records heart activity for less than 7 days (<7-day Holter monitor), or using a portable device that records heart activity for 7 to 30 days (7-30-day Holter monitor).

The investigators hypothesize that the burden of AF (severity and frequency of AF episodes) will increase over time, risk factors such as newly diagnosed hypertension will emerge, biomarkers indicating heart stress and damage will increase, and the left atrium will show signs of worsening function and increased size. The underlying idea is that patients with initially low AF burden might have a "young" form of AF that gradually worsens, increasing their risk of stroke. Therefore, the investigators will evaluate the progression of AF burden over time. Throughout the study, the investigators will regularly measure AF burden (frequency and severity of episodes), levels of specific biomarkers (e.g., MR-proANP, 0troponin), blood pressure, weight, and development of risk factors. Participants will be followed up to 24 months.

To gather data, the investigators will use recording of AF burden, echocardiography (imaging to assess heart structure and function), plasma biomarkers (blood tests to measure substances indicating heart health), and cardiac CT scans at the beginning and end of the study to assess heart health. This study aims to provide valuable insights into how AF evolves in stroke patients, potentially leading to better treatments and prevention strategies for reducing stroke risk.

Inclusion Criteria:

• Adult patients with cortical or subcortical, cryptogenic or non-cryptogenic acute ischemic stroke
• Any of the following types of AF:
• Paroxysmal AF known before stroke onset (KAF).
• Paroxysmal AF found on an admission or Emergency Department ECG (ECG-AFDAS)
• Paroxysmal AF found on 14-day Holter monitoring (PCM-AFDAS)

Exclusion Criteria:

• Patients not willing to consent
• Permanent or persistent AF
• Allergy to iodinated contrast agents