The following are key points to remember about this state-of-the-art article on systemic computed tomography (CT) methodology for the evaluation of subclinical leaflet thrombosis:

1. Subclinical leaflet thrombosis is relatively common following both transcatheter and bioprosthetic valve replacement, and has been described in a randomized trial of transcatheter aortic valve replacement (TAVR) as well as registry data. The clinical significance of this finding remains unclear.
2. Both transesophageal echocardiography (TEE) and cardiac computed tomography (CCT) have been used to characterize subclinical leaflet thrombosis, and a small study of 10 patients suggests good correlation between these imaging modalities. TEE has historically been the gold standard to identify subclinical leaflet thrombosis, but it represents an invasive study, and may be more operator dependent than CCT.
3. Imaging assessment should include evaluation of leaflet thickening and leaflet motion. Hypoattenuated leaflet thickening should prompt close assessment for possible reduction of leaflet motion. Significant reduction in leaflet opening is proposed to be defined as at least 50% reduction in actual to expected leaflet opening.
4. CCT requires specific protocols including the use of retrospective electrocardiography (ECG) gating without dose modulation to image the valve at multiple points in the cardiac cycle. ECG dose modulation (reduction of tube current to lower radiation dose for part of the cardiac cycle) should not be used in order to maintain high image quality throughout the cardiac cycle. This permits assessment of leaflet motion in both systole and diastole, and selection of the most motion-free and artifact-free images for evaluation of leaflet thickening. Studies should also be acquired with high spatial resolution and adequate tube voltage for good image quality. Additional assessments should include the depth of implant, stent frame expansion, and stent strut analysis.
5. When CCT images are inadequate or when CCT is contraindicated, TEE should be considered.
6. A systematic approach that assesses the valves using both two-dimensional and three-dimensional reconstructions is recommended. Bioprosthetic leaflet abnormalities should be identified by their location relative to the native leaflets, and standardized reporting is recommended.
7. The mechanisms of leaflet thrombosis are not yet established. Early data suggest that a relatively ventricular position of a TAVR prosthesis and low-flow states may be related to leaflet thrombosis.
8. The medical relevance of subclinical leaflet thrombosis remains unknown, although it is clear that anticoagulation can reverse leaflet hypoattenuation and improve leaflet motion. Current and planned studies will evaluate risk factors and optimal treatment of subclinical leaflet thrombosis.

Keywords: Artifacts, Cardiac Imaging Techniques, Cardiac Surgical Procedures, Diastole, Echocardiography, Transesophageal, Electrocardiography, Heart Valve Diseases, Heart Valve Prosthesis, Risk Factors, Stents, Systole, Thrombosis, Tomography, Tomography, X-Ray Computed, Transcatheter Aortic Valve Replacement

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