Regional myocardial microstructural assessment in aortic stenosis by cardiac diffusion tensor imaging

Introduction Aortic stenosis (AS) is a common valvular disease and one of the major causes of morbidity and mortality. Progressive valvular narrowing results in chronic pressure overload, compensatory left ventricular hypertrophy (LVH), and structural remodelling. Irreversible myocardial injury may develop before overt systolic dysfunction or adverse remodelling becomes evident. In this study, we use cardiac diffusion tensor imaging (cDTI) to investigate the relationship between segmental myocardial fibrosis and microstructural alterations in patients with AS. Purpose To explore whether segmental DTI parameters differ between late gadolinium enhancement positive (LGE+) and LGE-negative (LGE-) myocardium in the AS cohort. Methods Twenty-one patients with moderate/ severe AS underwent 3T CMR, including cine images, free-breathing spin-echo DTI (3 slices, 18 diffusion directions at b-values 100s/mm2, 200s/mm2, and 500s/mm2 using second-order motion-compensated (M2) gradients, resolution of 2.20*2.27*8mm3), tissue mapping pre- and post-contrast, and LGE. Segmental analysis was performed in the basal and mid-ventricular slices using the AHA model. LGE was quantified using a≥5 standard deviation threshold above the remote myocardium. DTI metrics included mean diffusivity (MD) (a measure of the freedom of water diffusion in the myocardium; increase in interstitial fibrosis), fractional anisotropy (FA) (a measure of directionality of water molecules; decrease in cardiomyocyte disorganisation), and secondary eigenvector angle (E2A) (a marker of sheetlet orientation). DTI parameters were compared between LGE+ and LGE- segments. Segmental native T1 and extracellular volume (ECV) were also assessed. Results LGE was present in 15 of 21 patients (71%). After exclusion of apical and artefact-affected segments, 169 segments were included, of which 43 (25%) were LGE +, and 126 (75%) were LGE-. LGE+ segments demonstrated significantly higher MD compared with LGE- segments (1.60±0.11 vs 1.56±0.09, p=0.017). FA was significantly lower in LGE+ compared with LGE- segments (0.29±0.05 vs 0.31±0.04, p=0.0139). There was no significant difference in E2A between the two groups (53±13 vs 52±14, p=0.721). Segmental native T1 and ECV did not differ significantly among them (T1: 1343±60 vs 1336±62 ms, p=0.506; ECV median 26% vs 26%, p=0.113). Within LGE+ segments, ECV correlated with segmental native T1 (r = 0.5152, p = 0.0008). Conclusions cDTI differentiates fibrotic from non-fibrotic segments even when native T1 and ECV were not significantly different at the segmental level. LGE+ segments demonstrate higher diffusivity and lower anisotropy, consistent with microstructural disorganisation in fibrotic myocardium in aortic stenosis. cDTI may provide complementary microstructural information beyond conventional tissue characterisation in pressure-overload remodelling. Larger studies are warranted to confirm clinical utility.Table 1.Demographic, CMR parametersFig 1.MD, FA, E2A in LGE+ and LGE- AS patients