Introduction:

Cardiac amyloidosis (CA) is an infiltrative cardiomyopathy caused by extracellular myocardial amyloid deposition. The most frequent variants are due to immunoglobulin light chains or transthyretin (ATTR). 99mTc-pyrophosphate (99mTc-PYP) scintigraphy is a molecular imaging technique that allows differentiation of the most common subtypes of AC. The present study analyzed the role of 99mTc-PYP and SPECT-CT in the evaluation of patients with clinical suspicion of CA.

Materials and methods:

99mTc-PYP and SPECT-CT were performed in 16 patients with clinical suspicion of AC, with an average age of 63 years. Qualitative analysis was performed on the planar and SPECT-CT images (Mediso, AnyScan), acquired 1-3 hours after the injection of the radiotracer. For the quantitative analysis of the planar images, the H/CL ratio (average counts obtained over the regions of interest of the heart and the contralateral hemithorax) was calculated. The study was considered positive for ATTR when the H/CL ratio was ≥1.5. The SPECT-CT images were interpreted to observe the distribution of the tracer at the cardiac and extracardiac level.

Results:

Myocardial uptake of 99mTc-PYP was identified in the left ventricle in 6 patients and in the right ventricle in 3 patients. In these cases, the H/CL ratio was >1.5. In the rest, myocardial uptake was ruled out, with a H/CL ratio of 1.5. Vascular pool activity was detected in the tomographic images of 7 patients and abnormal extracardiac bone uptake of traumatic/degenerative causes in 9 patients. Five patients presented diffuse hepatic uptake, without structural alteration on CT.

Conclusions:

99mTc-PYP is a clinically relevant technique in patients with suspected CA. It constitutes a minimally invasive tool, widely available, low cost and useful in diagnosis, and can guide the AC subtype. The information it provides also makes it possible to guide therapeutic options and provide additional prognostic information.

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