Microstructural assessment of hypertrophic cardiomyopathy with preserved left ventricular ejection fraction using second-order motion-compensated spin echo diffusion tensor cardiovascular magnetic resonance imaging

PURPOSE To investigate myocardial microstructural alterations in hypertrophic cardiomyopathy (HCM) with preserved left ventricular ejection fraction using second-order motion-compensated spin echo cardiac diffusion tensor imaging (M2-cDTI), and to determine whether cDTI can reveal abnormalities beyond late gadolinium enhancement (LGE). MATERIALS AND METHODS In this cross-sectional observational study, 41 patients with HCM and 21 healthy volunteers underwent 1.5 T CMR including cine, LGE, and M2-cDTI. All myocardial segments were categorised into three groups based on LGE characteristics, LGE-positive (signal intensity ≥ 6 standard deviations [SD] above reference myocardium-the relatively normal myocardium), LGE-grey (signal intensity 2-6 SD above reference myocardium), and LGE-negative (signal intensity < 2 SD above reference myocardium). RESULTS Global analysis revealed significantly elevated second eigenvector angle (E2A) in the HCM group compared with controls (44.04° ± 3.49 vs. 39.54° ± 3.70, p < 0.001). Initial segment-level comparisons showed higher E2A and lower FA in LGE-positive segments, whereas LGE-grey and LGE-negative segments showed higher E2A and FA than control segments. After accounting for intra-patient clustering, LGE classification remained significantly associated with E2A, with higher estimated marginal mean E2A values in LGE-negative, LGE-grey and LGE-positive segments than in controls (42.21°, 43.80° and 44.73° vs. 39.72°, respectively; all adjusted p < 0.05; Table 3), whereas the regional differences in FA were no longer statistically significant (F = 2.58, p = 0.052). CONCLUSION In vivo M2-cDTI may reveal altered myocardial diffusion characteristics in HCM, even in regions without evident LGE, highlighting its potential as a sensitive biomarker for early detection of myocardial abnormalities.