Quantitative ^99mTc-pyrophosphate myocardial uptake: Changes on transthyretin stabilization therapy

Area of Science:

• Cardiology
• Nuclear Medicine
• Radiology

Background:

• Transthyretin cardiac amyloidosis (ATTR-CA) diagnosis and monitoring rely on imaging techniques.
• Technetium-99m-pyrophosphate cardiac single-photon emission computed tomography (99mTc-PYP SPECT/CT) is an emerging tool for assessing ATTR-CA myocardial burden.
• The utility of 99mTc-PYP SPECT/CT in tracking longitudinal changes in ATTR-CA during therapy is not well-established.

Purpose of the Study:

• To evaluate longitudinal changes in cardiac ATTR amyloid burden using visual and quantitative 99mTc-PYP SPECT/CT.
• To assess the impact of transthyretin stabilization therapy on myocardial amyloid burden.
• To correlate changes in 99mTc-PYP uptake with alterations in cardiac biomarkers and function.

Main Methods:

• Prospective longitudinal cohort study of 23 ATTR-CA participants on transthyretin stabilization therapy.
• Quantitative 99mTc-PYP SPECT/CT analysis included standardized uptake values (SUVs), cardiac amyloid activity (CAA), and percent injected dose (%ID).
• Statistical analysis utilized the Wilcoxon signed-rank test for paired continuous and ordinal variables.

Main Results:

• Significant decrease observed in visual grade (P = 0.003) and quantitative 99mTc-PYP metrics: SUVmax (P = 0.011), CAA (P < 0.001), and %ID (P < 0.001).
• Serum transthyretin levels improved (P = 0.008).
• Echocardiographic parameters (global longitudinal strain, LV mass index, LV wall thickness) and biomarkers (NT-proBNP, eGFR) remained stable.

Conclusions:

• Favorable changes in 99mTc-PYP myocardial uptake suggest stabilization of myocardial ATTR amyloid burden during therapy.
• Stable echocardiographic parameters and biomarkers indicate that observed imaging changes may reflect stabilization rather than regression of amyloid burden.
• Further research is warranted to elucidate the clinical implications of these findings in ATTR-CA management.