Novel Phenotyping of the Myocardium by Diffusion Tensor Cardiovascular Magnetic Resonance Dr Zohya Khalique

Introduction The heart has a complex microarchitecture facilitating its function. The helical cardiomyocyte arrangement (left-handed in the epicardium through to right-handed in the endocardium) drives torsion. Sheetlets are aggregated cardiomyocytes that realign from wall-parallel in diastole, to wall-perpendicular in systole. This sheetlet mobility is integral to wall thickening. Diffusion tensor cardiovascular magnetic resonance (DT-CMR) is a novel, non-invasive technique informing about myocardial microstructure, including cardiomyocytes and sheetlets. Few in-vivo human studies exist. This research aims to investigate microstructural changes in disease and assess the utility of DT-CMR as a novel phenotyping tool.

Methods Biphasic DT-CMR was performed in controls and in patients with dilated cardiomyopathy (DCM), including recovered dilated cardiomyopathy (R-DCM) and congenital disease, as exemplified by situs inversus totalis (SIT). Two main DT-CMR sequences, stimulated echo acquisition mode (STEAM) and second-order motion-compensated spin echo (M2-SE) were compared in a hypertrophic cardiomyopathy cohort. Volumetric analysis, strain assessment and late gadolinium imaging was performed.

Results In DCM sheetlet mobility was reduced, with a more diastolic orientation at both cardiac phases. In R-DCM, despite normalisation of left ventricular size and ejection fraction, microstructural abnormalities persisted, with impaired sheetlet mobility. In SIT, there was gross cardiomyocyte derangement, with an overall pattern of inversion of the helical arrangement basally, transitioning to a more normal pattern apically. This microstructural derangement led to reduced torsion and strain. Finally, STEAM and M2-SE results differ due to intrinsic differences in the two sequence types. Overall STEAM was more reliable than M2-SE in biphasic DT-CMR.

Conclusion DT-CMR identified novel cardiomyocyte and sheetlet abnormalities in-vivo. DT-CMR offers unique insight into microstructural changes in disease, and this work supports its potential as a powerful clinical tool assessing course and prognosis in cardiac conditions.