Hypoattenuated leaflet thickening (HALT) and reduced leaflet motion (RELM) of aortic bioprostheses: An imaging finding or a complication?

Transcatheter aortic valve implantation is a safe and effective therapy for patients with symptomatic severe aortic stenosis, with randomized data demonstrating outcomes at least equivalent to surgical aortic valve replacement across the spectrum of surgical risk. There has been substantial recent interest in the occurrence of hypoattenuated leaflet thickening and reduced leaflet motion, which are imaging features detected on computed tomography of patients who have received aortic bioprostheses. These phenomena may represent subclinical leaflet thrombosis with theoretical potential downstream effects on valve durability or thrombotic complications in the form of stroke. This review will discuss definitions, predictors, mechanisms, diagnosis, and natural history. We will also examine the frequency with which hypoattenuated leaflet thickening and reduced leaflet motion occur after both transcatheter and surgical aortic bioprostheses, and the clinical implications and potential impact on valve function, as well as strategies for prophylaxis and treatment.