Diagnostic value of heart-to-mediastinum ratio in 99mTc-pyrophospate SPECT/CT for transthyretin cardiac amyloidosis

Background In transthyretin cardiac amyloidosis (ATTR-CA), Tc-99m-pyrophosphate myocardial scintigraphy (Tc-99m-PYP) is a diagnostic tool that utilizes visual and quantitative evaluation. However, false positive cases can occur because of tracer accumulation in the blood. We investigated the effectiveness of the heart-to-mediastinum (H/M) ratio of Tc-99m-PYP in ATTR-CA diagnosis.Methods We retrospectively included 164 patients who underwent Tc-99m-PYP single-photon emission computed tomography/computed tomography between March 2019 and January 2022. The diagnostic accuracy of ATTR-CA was examined by the heart-to-contralateral lung (H/CL) and H/M ratio calculated at 3 hours post-tracer administration.Results After the exclusion of patients who did not undergo endomyocardial biopsy, 30 patients (15 each with ATTR-CA and without ATTR-CA) were included. The receiver operating characteristic curve used to distinguish ATTR-CA from non-ATTR-CA patients revealed an area under the curve of 0.986 and 0.943, respectively. A H/M ratio of > 1.41 identified ATTR-CA patients with a sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 100, 93.3, 93.3, and 100%, respectively. Conversely, an H/CL ratio of > 1.3 identified ATTR-CA patients with 100% sensitivity, 40.0% specificity, 62.5% PPV, and 100% NPV.Conclusion The H/M ratio obtained at 3 hours post-injection has the potential to be a novel indicator for ATTR-CA.

Automated summary

The heart-to-mediastinum (H/M) ratio of Tc-99m-PYP obtained at 3 hours post-injection has the potential to be a novel indicator for the diagnosis of ATTR-CA. A ratio greater than 1.41 can accurately identify ATTR-CA patients with a sensitivity of 100%.