CMR Diffusion Tensor Imaging Provides Novel Imaging Markers of Adverse Myocardial Remodeling in Aortic Stenosis
Authors: Gotschy Alexander , von Deuster Constantin , Weber Lucas , Gastl Mareike , Schmiady Martin O. , van Gorkum Robbert J. H. , Stimm Johanna , von Spiczak Jochen , Manka Robert , Kozerke Sebastian , Stoeck Christian T. 
Published: August 2020

Objectives

This study sought to determine microstructural cardiac remodeling in aortic stenosis (AS) and its reversibility following valve replacement using cardiovascular magnetic resonance (CMR) diffusion tensor imaging (DTI).

Background

Myocardial involvement in AS, such as focal and diffuse fibrosis is associated with worse outcome, even after timely aortic valve replacement (AVR). Alterations of myofiber architecture and myocardial diffusion may precede fibrosis, but its extent and reversibility after AVR are unknown.

Methods

Patients with isolated severe AS (n = 21, 62% male; mean age 75 years) and sex-matched senior control subjects underwent prospective CMR DTI. Changes in the DTI parameters: mean diffusivity (MD), fractional anisotropy (FA) as well as helix angle (HA) and absolute E2A sheet angle (E2A) were quantified and compared with native T1 and extracellular volume (ECV) as standard CMR markers of myocardial fibrosis. Six months after AVR eleven patients were scheduled for a follow-up CMR.

Results

In AS patients, significantly elevated MD (p = 0.002) and reduced FA (p< 0.001) were measured when compared to controls. Myocyte aggregate orientation exhibited a steeper transmural HA slope (p< 0.001) and increased absolute E2A sheet angle (p< 0.001) in AS. Six months post AVR, the HA slope (p< 0.001) was reduced to the level of healthy controls and MD (p = 0.014), FA (p = 0.011) and E2A (p = 0.003) showed a significant regression towards normal values. In contrast, native T1 was similar in AS and controls and did not change significantly after AVR. ECV showed a non-significant trend (p = 0.16) to higher values after AVR.

Conclusion

In patients with severe aortic stenosis, CMR DTI provides a set of parameters that identifies structural and diffusion abnormalities, which are largely reversible after AVR. DTI parameters showed proportionally greater changes in response to AS and AVR compared to metrics of myocardial fibrosis and may, therefore, aid risk stratification in earlier stages of severe AS.

Condensed Abstract

CMR diffusion tensor imaging (DTI) is a novel, noninvasive technique that allows for the assessment of myocardial microstructure in diseased hearts. We used CMR DTI to investigate myocardial involvement in patients with aortic stenosis (AS) before and after aortic valve replacement (AVR). Measures of tissue diffusion as well as parameters of myocyte orientation were significantly altered by AS and showed a clear trend towards normalization after AVR. Conventional markers of myocardial fibrosis (native T1 & extracellular volume) did not change significantly after AVR. Therefore, CMR DTI may unlock a new level of detail for phenotyping myocardial involvement in AS with potential value for improved risk stratification by visualizing earlier stages of adverse remodeling.