Diffusion Tensor Cardiac Magnetic Resonance (DT-CMR) for Contrast-Free Detection of Early Cardiac Amyloidosis in Carpal Tunnel Syndrome (RF_TH_208)

Amyloidosis is a systemic disease caused by the deposition of amyloid fibrils with misfolded protein. Cardiac amyloidosis (CA) occurs when these amyloid fibrils deposit in the myocardium, which leads to diastolic dysfunction and subsequent heart failure. Research has shown that CA is oftentimes preceded by carpal tunnel syndrome (CTS). A study found that 10.2% of patients who underwent carpal tunnel release surgery had amyloid present in the tenosynovial biopsy4.

Current gold standards to diagnose CA include heart tissue biopsy and pyrophosphate scintigraphy scan, whose drawbacks include invasiveness and radiation exposure, respectively. Diffusion tensor cardiac magnetic resonance (DT-CMR) is an in-vivo, non-invasive, and contrast-free imaging technique that can assess cardiac amyloid infiltration by analyzing myocardial microstructure. This study applied DT-CMR to CTS patients with confirmed wrist amyloid in an attempt to screen for early CA. Earlier detection of CA would allow for the earlier initiation of treatment and better patient outcomes. 

Methods:

DT-CMR was performed on 17 CA patients, 8 CTS patients with confirmed wrist amyloid, 17 patients with hypertrophic cardiomyopathy or hypertrophic obstructive cardiomyopathy (HCM/HOCM), and 17 healthy controls. The diffusion scheme was an ECG-gated free-breathing second-order motion-compensated spin echo acquisition obtained in systole1,2 (ZOOMit, resolution = 2.7mm x 2.7mm, slice thickness = 8mm, 128x48 matrix, 5 slices, 12 diffusion directions, 1 average b0 = 50 s/mm2, 8 averages b=500s/mm2, TE = 59ms). 

Mean diffusivity (MD), fractional anisotropy (FA), helix angle transmurality (HAT), secondary eigenvector of diffusion (E2A), T1, and T2 were calculated from respiratory motion-corrected images1,3. ANOVA was used to compare the means of each parameter. 

Results:

Figure 1 shows sample MRI overlay plots for the four diffusion parameters, T1, and T2 across the four groups analyzed. Parameters were calculated for the myocardium around the left ventricle. 

Figure 2 shows scatterplots of the parameter values. MD was significantly elevated in CA compared to CTS patients (p=0.003). Likewise, MD was significantly higher in CTS patients compared to healthy controls (p=0.0464). FA was significantly reduced in both CA and CTS compared to healthy (p=0.0097 and p=0.0092, respectively). E2A was significantly increased in CA compared to healthy participants (p< 0.0001). T1 was significantly higher in CA patients compared to all other groups. HAT and T2 were not significantly different between the groups analyzed. 

Conclusion:

Diffusion parameters MD and FA effectively discriminate between the myocardial microstructure of healthy patients and those with CTS and CA. These results are the first to show that DT-CMR can detect evidence of cardiac amyloidosis in CTS patients earlier than conventional diagnostic techniques, offering the possibility of earlier treatment initiation and improving CA prognosis.