Abstract 19916: Human Valve Leaflet Tissue Characterization In Severe Aortic Stenosis
Introduction: Aortic valve stenosis (AS) is a growing health problem. The pathophysiology underlying active remodeling of leaflet tissue remains incompletely understood, but may involve atherogenic and osteogenic processes. Imaging these changes may enhance understanding of leaflet remodeling and valvular stenosis progression and identify new targets for medical therapy.
Hypothesis: We assessed the hypothesis that multiparametric magnetic resonance imaging (mMRI) could characterize and quantify lipid, fibrous, and calcified tissues within explanted aortic valve leaflets of patients with severe AS.
Methods: Aortic valve leaflets were explanted from subjects with severe AS at the time of valve surgery. Leaflets were imaged ex vivo by 1.5 Tesla MRI using a 23 mm circular receiver coil and 3 gradient echo sequences with T1, moderate T2 (mT2), and proton density (PD), (slice thickness 1.5mm). Histopathological analysis was performed on co-registered slices to identify and measure calcified (H&E), fibrous (Picrosirius red) and lipid-rich tissues (Oil-red-O). Areas and mean gray values were measured in 3 weightings by validated software.
Results: 492 regions of interest from 30 aortic valve leaflets were studied. Fibrous, lipid-rich and calcified tissues consisted of 43%, 29% and 28% of total leaflet areas, respectively. Total leaflet area and the areas of calcified, fibrous and lipid-rich tissues measured by MRI matched closely with those measured by histopathology (Bland Altman p for difference in variance = NS for all tissues). All 3 weightings provided significant discrimination between median gray values for calcified, fibrous and lipid-rich tissues (p<0.0001 for T1, mT2 and PD). A best fit equation integrating the gray value data from all 3 weightings (T1, mT2 and PD) allowed mMRI to identify aortic valve leaflet calcified, fibrous, and lipid-rich tissues with areas under the ROC curve of 0.92, 0.81 and 0.72 respectively.
Conclusions: Aortic valve leaflet characteristics including tissue composition, distribution, and area may be measured by mMRI with superior accuracy. The refinement of this approach to assess valve leaflet characteristics by MRI in patients may further elucidate the complex metabolic pathways underlying AS progression.
- © 2010 by American Heart Association, Inc.