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Hypoattenuated Leaflet Thickening After Transcatheter Aortic Valve Replacement: Expanding the Evidence Base but Questions Remain.

In 2015, as transcatheter aortic valve replacement (TAVR) was gaining momentum as an alternative to surgery, a troubling report was published about subclinical leaflet thrombosis.1 The focus was on reduced leaflet motion, which was observed in 40% of patients in a clinical trial cohort and 13% of patients in 2 registries. Most patients examined had been treated with TAVR, but the finding was also observed in patients treated with a surgical bioprosthetic valve. The reduced leaflet motion was associated with hypoattenuating opacities at the base of the less mobile leaflets, but no differences were observed in the transvalvular gradients. Anticoagulation was associated with a lower incidence of reduced leaflet motion and resolution of it when it was observed. Reduced leaflet motion was not associated with death, stroke, or myocardial infarction but the pooled registry cohort showed a higher incidence of transient ischemic attack among those with reduced leaflet motion. This provocative report prompted several questions about subclinical bioprosthetic valve thrombosis: (1) What is the incidence?; (2) When does it occur?; (3) Is there a difference between surgical and transcatheter valves or between individual valve types?; (4) Does it affect valve hemodynamics in the short-term or long-term or both?; (5) Is it associated with structural valve deterioration and durability?; (6) Does it affect clinical outcomes such as stroke, transient ischemic attack, thromboembolism, heart failure hospitalizations, and mortality?; and (7) Does antiplatelet or anticoagulant therapy reduce the incidence or aid in resolution? Since the initial report, progress has been made in addressing these important questions. The gold standard for diagnosis of subclinical leaflet thrombosis after surgical or TAVR is 4-dimensional computed tomography (CT) scan. The characteristic finding on the 4-dimensional CT scan is a hypoattenuating opacity at the base of valve leaflets; this is referred to as hypoattenuated leaflet thickening (HALT). Hypoattenuation affecting motion (HAM) is defined as reduction of leaflet motion related to HALT. In response to the 2015 report, the U.S. Food and Drug Administration mandated that the low-risk TAVR trials include a CT imaging substudy to evaluate the incidence, predictors, and outcomes of HALT.