Oral Abstract Session
SCMR 22nd Annual Scientific Sessions
Cardiac amyloid is a disease of microstructural protein deposition, where light chains (AL) or transthyretin (ATTR) infiltrate the myocardium. Currently diffusion tensor cardiovascular magnetic resonance (DT-CMR) is the only non-invasive tool able to dynamically assess the cardiac microstructure in vivo. We present initial data on mean diffusivity (MD), micro-organisation via fractional anisotropy (FA) and sheetlet orientation via second eigenvector angle (E2A) in patients with cardiac amyloid, hypertrophic cardiomyopathy (HCM) and controls.
DT-CMR was performed in 17 cardiac amyloid (7 AL, 10 ATTR), 8 HCM and 10 controls using a STEAM-EPI sequence at 3T . Volumetric, strain, T1 mapping and late gadolinium enhancement (LGE) imaging was also performed. MD, FA, E2A, functional parameters, native T1 and extracellular volume (ECV) were calculated. LGE was scored using the query LGE (QALE) system . The Mann-Whitney test was used for statistical analysis.
Baseline characteristics of the three groups were well-balanced. Amyloid patients had reduced left ventricle (LV) ejection fraction and strain, but higher indexed LV mass and native T1 compared to controls. As expected, LVEF was lower whilst native T1 and ECV were higher in amyloid compared to HCM.
Example diffusion parameter maps from an amyloid, HCM and control subject are shown in Figure 1.
Median [IQR] diastolic MD was 1.44 [1.36-1.54] x10-3mm2/s in amyloid, significantly higher than HCM (1.21 [1.09-1.24] x10-3mm2/s) and controls (1.15 [1.03-1.18] x10-3mm2/s), both p<0.001. A similar pattern was seen for systolic MD (Figure 2A).
Diastolic FA was significantly lower in amyloid (0.43 [0.40-0.45]) compared to HCM (0.55 [0.50-0.57]) and controls (0.55[0.52-0.60], both p<0.001). A similar pattern was seen for systolic FA (Figure 2B).
Diastolic E2A in amyloid was 47 [38-52]°, lower than HCM 56 [47-60]°, p=0.03 and higher than controls 24 [18-31]°, p<0.001. Systolic E2A in amyloid was 69 [65-73]°, lower than HCM 74° [70-78], p=0.04, and similar to controls 65° [59-68], p=0.08, as in Figure 3. E2A mobility in amyloid (23 [18-32]°) was reduced compared to controls (40 [35-44]°, p=0.001).
No significant differences existed in MD, FA or E2A between ATTR and AL despite a higher QALE score (16 [14-16] vs 13 [8-14], p=0.007) and trend to higher ECV (0.58 [0.51-0.63] vs 0.49 [0.43-0.59], p=0.27) in the ATTR group.
DT-CMR is sensitive to microstructural changes in cardiac amyloid . We show decreased FA and elevated MD suggest microstructural disorganisation and increased freedom of diffusion, beyond that seen in HCM. Using STEAM DT-CMR, the lower biphasic E2A distinguishes amyloid from HCM. Finally, despite the greater amyloid burden in ATTR, microstructural findings did not differ from AL. DT-CMR can characterise the microstructure in cardiac amyloid, giving new in vivo insight into the interaction between the myocardium and amyloid infiltration.