A Study to Learn How Well the Study Treatment Asundexian Works and How Safe it is Compared to Apixaban to Prevent Stroke or Systemic Embolism in People With Irregular and Often Rapid Heartbeat (Atrial Fibrillation), and at Risk for Stroke

Researchers are looking for a better way to treat people with atrial fibrillation and prevent stroke or systemic embolism (blood clots travelling through the blood stream to plug another vessel).Atrial fibrillation is a condition of having irregular and often rapid heartbeat. It can lead to the formation of blood clots in the heart which can travel through the blood stream to plug another vessel, and like this lead to serious and life-threatening conditions, such as a stroke. A stroke occurs because the brain tissue beyond the blockage no longer receives nutrients and oxygen so that brain cells die. As strokes arising from atrial fibrillation can involve extensive areas of the brain, it is important to prevent them.Blood clots are formed in a process known as coagulation. Medications are already available to prevent the formation of blood clots. When taken by mouth (orally), they are known as oral anticoagulants (OACs) including apixaban. OACs decrease the risk of the above-mentioned serious and life-threatening conditions. The main side effect of OACs is an increase of the risk of bleeding.The study treatment asundexian is a new type of anticoagulant currently under development to provide further treatment options. The way it works, it aims to further improve the standard of care with regard to the risk of bleeding.The main purpose of this study is to collect more data about how well asundexian works to prevent stroke and systemic embolism and how safe it is compared to apixaban in people with atrial fibrillation and at high risk for stroke.To see how well the study treatment asundexian works researchers compare:how long asundexian works well andhow long apixaban works well after the start of the treatment. Working well means that the treatments can prevent the following from happening:stroke and/orsystemic embolism. The study will keep collecting data until a certain number of strokes or embolisms happen in the study.To see how safe asundexian is, the researchers will compare how often major bleedings occur after taking the study treatments asundexian and apixaban, respectively. Major bleedings are bleedings that have a serious or even life-threatening impact on a person's health.The study participants will be randomly (by chance) assigned to 1 of 2 treatment groups, A and B. Dependent on the treatment group, the participants will either take the study treatment asundexian by mouth once a day or apixaban by mouth twice a day for approximately 9 - 33 months.Each participant will be in the study for approximately 9 - 34 months. There will be visits to the study site every 3 to 6 months and up to 7 phone calls. Those participants who do not want or are unable to have visits to the study site may join the study remotely in selected countries. All visits for these participants will be done using electronic devices.During the study, the study team will:take blood samplesdo physical examinationsexamine heart health using an electrocardiogram (ECG)check vital signs such as blood pressure and heart ratedo pregnancy testsask the participants questions about their quality of lifeask the participants questions about how they are feeling and what adverse events they are having.An adverse event is any medical problem that a participant has during a study. Doctors keep track of all adverse events that happen in studies, even if they do not think the adverse events might be related to the study treatments.

Inclusion Criteria:18 years of age or older (at legal age of consent according to local legislation) at the time of signing the informed consentAtrial fibrillation documented by ECG evidence with an indication for indefinite treatment with an oral anticoagulantCHA2DS2-VASc score ≥ 3 if male or ≥ 4 if female, OR CHA2DS2-VASc score of 2 if male or 3 if female and enrichment criteria.Exclusion Criteria:Mechanical heart valve prosthesisModerate-to-severe mitral stenosis at the time of inclusion into the studyAtrial fibrillation only due to reversible causeRequirement for chronic anticoagulation for a different indication than AF