The Nordic Aortic Valve Intervention Trial 4 (NOTION-4) is a clinical study focused on patients who have undergone a successful procedure known as *transcatheter aortic valve implantation* (TAVI). This procedure involves placing a new valve in the heart without removing the old, damaged valve. The study aims to explore the effects of different *anti-thrombotic therapies* on a condition called *subclinical leaflet thickening* in the new valve. Subclinical leaflet thickening, also known as HALT, refers to a situation where the leaflets of the valve become thicker without causing noticeable symptoms. This condition is assessed using a special imaging technique called *cardiac CT*.

The study involves several medications, including *Apixaban*, *Acetylsalicylic Acid* (commonly known as aspirin), *Rivaroxaban*, *Dabigatran Etexilate*, *Edoxaban*, *Clopidogrel*, and *Warfarin Sodium*. These medications are used to prevent blood clots, which can be a concern after valve replacement procedures. Participants in the study are randomly assigned to receive one of these medications or a placebo. The purpose of the study is to understand how these medications affect the thickening of the valve leaflets over time.

Throughout the study, participants will undergo regular check-ups and imaging tests to monitor the condition of their heart valves. The study will track the number of patients experiencing leaflet thickening at various intervals, such as 3 months, 1 year, 3 years, and 5 years after the TAVI procedure. Additionally, the study will observe any related health events, such as strokes or bleeding, and assess overall health outcomes like mortality and quality of life. The study is expected to continue until 2030, providing valuable insights into the long-term effects of different anti-thrombotic treatments on heart valve health.