The purpose of this observational study is to investigate whether blood tests related to blood clotting are associated with established clinical stroke risk scores, the total amount of device-detected atrial fibrillation recorded by an implanted cardiac device, and ultrasound measurements of the heart in people with device-detected atrial fibrillation. The study will also evaluate whether these baseline measurements are associated with future clinical outcomes and may improve future stroke risk assessment.

Device-detected atrial fibrillation is an irregular heart rhythm detected by implanted cardiac devices such as pacemakers, implantable cardiac monitors, and implantable defibrillators. It is often brief and does not cause symptoms. Although it increases the risk of stroke and systemic embolism, the risk is lower than in people with clinically diagnosed atrial fibrillation. As a result, it remains difficult to identify which patients are most likely to benefit from blood-thinning medication, which reduces the risk of stroke but also increases the risk of bleeding.

The study will include 222 participants with implanted cardiac devices, including 111 participants with device-detected atrial fibrillation and 111 age-, sex-, and cardiac device indication-matched control participants without device-detected atrial fibrillation. At baseline, participants will undergo blood sampling, ultrasound examination of the heart, and routine device interrogation. Information on medical history and established clinical stroke risk factors will also be collected. The implanted cardiac device will be used to determine the total amount of device-detected atrial fibrillation recorded during the year before study inclusion.

The baseline analyses will investigate whether established clinical stroke risk scores, the total amount of device-detected atrial fibrillation, and heart ultrasound findings are associated with changes in blood clotting that may indicate an increased tendency to form blood clots. The study will evaluate both primary and additional blood clotting markers to improve the understanding of the biological mechanisms underlying thromboembolic risk in device-detected atrial fibrillation.

Participants will subsequently be followed for 10 years to determine whether baseline blood clotting markers, the total amount of device-detected atrial fibrillation, heart ultrasound findings, and clinical stroke risk scores are associated with future clinical outcomes, including stroke, systemic embolism, hospitalization, death, progression to clinically diagnosed atrial fibrillation, and initiation of oral anticoagulant therapy.

The findings may improve the understanding of thromboembolic risk in people with device-detected atrial fibrillation and support the development of more individualized approaches to future stroke risk assessment and treatment.