Quantitative 99m Tc-pyrophosphate myocardial uptake: Changes on transthyretin stabilization therapy.

Background: Quantitative technetium-99m-pyrophosphate cardiac single-photon emission computed tomography ( ^99m Tc-PYP SPECT/CT) is an emerging method for estimating myocardial burden of transthyretin cardiac amyloidosis (ATTR-CA), but its efficacy in monitoring longitudinal changes remains uncertain. We aimed to investigate longitudinal changes in cardiac ATTR amyloid burden following transthyretin stabilization therapy using visual and quantitative ^99m Tc-PYP SPECT/CT and to relate these with changes in cardiac biomarkers and function.
Methods: This prospective longitudinal cohort study investigated changes in ^99m Tc-PYP SPECT/CT in 23 participants with ATTR-CA on transthyretin stabilization therapy (median: 2.6 years). Quantitative analysis included left ventricular (LV) standardized uptake values (SUVs) (SUV _max , SUV _mean ), cardiac amyloid activity (CAA; SUV _mean ∗LV activity volume), and percent injected dose (%ID) (mean activity concentration∗LV activity volume/injected activity), calculated using a threshold of >1.5 times left atrial blood pool activity concentration on SPECT/CT. Longitudinal changes of paired continuous and ordinal variables were analyzed using Wilcoxon signed-rank test.
Results: Following therapy, visual grade decreased significantly (P = 0.003). Several quantitative ^99m Tc-PYP metrics also decreased significantly: SUV _max (median -0.75, P = 0.011), CAA (median: -406.6, P < 0.001), and %ID (median: -0.45, P < 0.001). Serum transthyretin levels improved (median: +6.5 mg/dL, P = 0.008). Echocardiographic parameters (global longitudinal strain, LV mass index, and LV wall thickness), N-terminal pro-B-type natriuretic peptide, and estimated glomerular filtration rate remained stable.
Conclusions: Favorable changes in ^99m Tc-PYP myocardial uptake were observed in participants on transthyretin stabilization therapy, whereas echocardiographic parameters and biomarkers remained stable. These results likely signify myocardial ATTR amyloid stabilization rather than amyloid burden regression. Further investigation is needed to understand the implications of these findings.
(Copyright © 2024 American Society of Nuclear Cardiology. Published by Elsevier Inc. All rights reserved.)