Cardiac amyloidosis other imaging findings

The initial imaging modality used in patients with suspected cardiac amyloidosis is echocardiography. The diagnosis of ATTR cardiac amyloid can then be confirmed with a nuclear scan (99mTc-PYP imaging), which can then guide the management.

• 99mTechnetium-pyrophopshate (99mTc-PYP) is a widely available radiotracer.
• In conjunction with a cardiac or chest SPECT, 99mTc-PYP is infused and then the images are examined for visual interpretation and quantification of the degree of myocardial uptake.^[1]
• Qualitatively, myocardial uptake patterns are either absent, focal, diffuse, or focal on diffuse.
• A diffuse pattern is suggestive of ATTR cardiac amyloid.
• Quantitatively, radiotracer uptake in the the region of interest (ROI) in the heart (H) is compared to the uptake in the contralateral lung (CL) at 1 hour after tracer injection, which yields an H/CL ratio.
• A H/CL ratio of ≥ 1.5 is suggestive of ATTR cardiac amyloid.
• Alternatively, uptake in the ROI can be visually compared to the rib at 3 hours after tracer injection, with a visual score grade of > 2 (indicating uptake equal to that of the rib) suggestive of ATTR cardiac amyloid.^[2]

• Direct detection of amyloid fibrils is possible using molecular imaging using amyloid-binding PET tracers, such as:
  • 11-Pittsburgh compound-B
  • F-18-florbetapir
  • F-18-florbetaben
• Using these PET tracers enables to:
  • Measure global and regional amyloid burden deposited in the myocardium
  • Detect molecular changes in the fibril composition
• Tracer uptake can be assessed visually or using a number of indexes such as: target to-background ratio, myocardial retention index, and myocardial standardized uptake value.
• These tracers might provide the opportunity to evaluate cardiac and systemic amyloid deposits throughout the whole body (for example in AL amyloidosis)

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