Computed tomography-derived Hounsfield units for the differentiation between thrombosis and leaflet fibrosis/calcification in bioprosthetic heart valves

Thrombosis and leaflet fibrosis/calcification are common causes of bioprosthetic heart valve (BHV) dysfunction. Distinguishing between these entities is crucial for patient management and choosing the optimal treatment modality. The aim of our study was to test the hypothesis that computed tomography angiography (CTA)-derived Hounsfield units (HU) can differentiate between thrombosis and leaflet fibrosis/ calcification in patients with suspected BHV dysfunction.

Valvular leaflet HU were assessed in 95 patients (derivation cohort) undergoing CTA 7+/-10 days after BHV implantation showing signs of subclinical leaflet thrombosis (hypoattenuated leaflet thickening - HALT). A second (validation) cohort included 46 patients undergoing CTA for suspected BHV dysfunction 4.0±4.1 years after valve replacement.

In the derivation cohort median HU was 87 (interquartile range, IQR77;96). In the validation cohort, patients with resolution of findings in a follow up CTA after newly initiated anticoagulation ("thrombosis" subgroup, 19 patients) similarly demonstrated HU of 87 (IQR74;100) (p=0.816). In contrast, patients without improvement under oral anticoagulation ("leaflet fibrosis/calcification" subgroup, 27 patients) exhibited a median of 137 HU (IQR116;164, p<0.001 vs. thrombosis subgroup, Figure). In multivariable cox regression analysis, lower Hounsfield units (HU) were an independent predictor of thrombosis. C-statistics demonstrated an area under the receiver operating characteristic curve of 0.94±0.02 (CI 0.897-0.983, p<0.001) with a value of 105 HU resulting in a sensitivity of 84% and a specificity of 91% for the differentiation between thrombosis and leaflet fibrosis/calcification.

A value of 105 Hounsfield units on CTA provides good discriminatory power to differentiate between thrombosis and leaflet fibrosis/calcification after bioprosthetic valve replacement.