Clinical valve thrombosis and subclinical leaflet thrombosis in transcatheter aortic heart valves: clinical manifestations, diagnosis, and treatment

During the last decade, transcatheter aortic valve replacement (TAVR) has rapidly expanded as an alternative to surgical aortic valve replacement (SAVR) in patients with symptomatic severe aortic valve stenosis (AS) and increased surgical risk. In TAVR, a bioprosthetic valve is positioned within the stenotic native aortic valve. Although favorable short- and medium-term outcomes have been reported, thrombosis of the transcatheter heart valve (THV) has occurred, with two different entities being described: clinical valve thrombosis and subclinical leaflet thrombosis. In clinical valve thrombosis, an increase in transvalvular gradient appears as a result of obstructive thrombus formation, which eventually leads to symptoms of heart failure. Subclinical leaflet thrombosis is an incidental finding, characterized by a thin layer of thrombus covering the aortic site of the leaflet—called hypo-attenuating leaflet thickening (HALT)—as described on and defined by 4-dimensional computed tomography (4DCT) imaging. This phenomenon may affect motion of the leaflets and is then classified as hypo-attenuation affecting motion (HAM). Even in the case of HAM, the transvalvular pressure gradient remains within the normal range. Clinical valve thrombosis requires treatment, whereas the clinical impact and need for intervention in subclinical leaflet thrombosis is uncertain. Anticoagulant therapy protects against and resolves both clinical valve thrombosis and subclinical leaflet thrombosis, but studies exploring different antithrombotic strategies after TAVR are ongoing. This review summarizes currently available literature within the field of THV thrombosis and provides recommendations for a patient-tailored approach in TAVR patients, although guidelines are still lacking.