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Abstract
Introduction Cardiac amyloidosis is a disease of infiltration, typically by light chains (AL) or transthyretin (ATTR). We studied cardiac amyloidosis using diffusion tensor cardiovascular magnetic resonance (DT-CMR), which is the only non-invasive tool able to assess cardiac microstructure in-vivo.
Methods and results Biphasic STEAM DT-CMR was successfully performed in 20 cardiac amyloidosis patients (10 AL, 10 ATTR) and 10 age and sex matched controls. Compared with controls, amyloid patients had higher mean diffusivity (MD); median [IQR] 1.46 [1.36–1.54] × 10−3 mm2/s vs 1.15 [1.03–1.20] × 10−3 mm2/s (p<0.001), shown in figure 1A. MD correlated with T1 (R2=0.76, p<0.001) and extracellular volume (ECV) (R2=0.47, p=0.004).
Diffusivity biomarkers differ significantly in cardiac amyloidMean diffusivity is significantly higher in cardiac amyloid (p<0.001) at both cardiac phases, reflecting increased freedom of diffusion in the expanded myocardium (panel A). In panel B, FA is significantly reduced (p<0.001) at both cardiac phases, reflecting the greater disorganisation of the infiltrated myocardium
Amyloid patients had lower fractional anisotropy (FA) compared to controls; 0.43 [0.39–0.45] vs (0.55 [0.52–0.60], p<0.001), as shown in figure 1B. FA inversely correlated with T1 (R2=0.59, p<0.001). Amyloid patients had elevated diastolic E2A and reduced E2A mobility (both <0.001).
Segmental analysis for co-location of FA and MD with ECV amyloid infiltration showed good correlation (both p<0.001). Example maps are shown in figure 2. There was no significant difference in MD, FA or E2A mobility between amyloid subtypes.
MD and FA map the location and extent of amyloid depositionExample maps from an AL and an ATTR patient are shown. In the top row ECV maps reflect the burden of amyloid. MD maps in the second row show areas of abnormally elevated MD in orange and red. Abnormally reduced FA is orange-green (third row). The MD and FA maps show co-location of the areas of elevated MD and reduced FA with amyloid as shown by ECV.
Conclusion In cardiac amyloidosis, DT-CMR characterises the microstructural effects of infiltration, and increases in MD show good correlation with increases in ECV. The novel insights from DT-CMR offer a deeper understanding of pathophysiological mechanisms in cardiac amyloidosis. With further development, DT-0CMR might offer a gadolinium free assessment of amyloid burden, which is of particular value in renal failure.