Optimizing cardiac amyloidosis assessment: utility of 1-h and 3-h ^99mTc-PYP imaging

Transthyretin amyloid cardiomyopathy (ATTR-CM), characterized by the extracellular deposition of an insoluble amyloid protein in the heart, is one of the main causes of heart failure in elderly patients. In this study, our primary objective was to explore the diverse applications and temporal significance of 1-h and 3-h imaging using ^99mTc-PYP in the context of ATTR-CM. Additionally, we compared tracer kinetics in the heart and bone to comprehensively assess the diagnostic advantages and time-related considerations associated with these two incubation periods.

Twenty-seven patients at Nagasaki University Hospital who underwent ^99mTc-PYP planar, and SPECT cardiac imaging were classified into two groups (ATTR-CM-positive and -negative groups) based on the American Heart Association statement. Cardiac retention was assessed with both a semiquantitative visual score and a quantitative analysis. To assess bone accumulation, a ROI with an equal volume was drawn on the sternum and calculated as the bone-to-contralateral ratio (B/CL). We also evaluated correlation between heart-to-contralateral lung (H/CL) ratio and left ventricular wall thickness.

Among patients who underwent ^99mTc-PYP imaging, the H/CL ratio was significantly higher at 1 h than at 3 h regardless of the group (from 2.20 ± 0.36 to 1.99 ± 0.35, p < 0.01 in the positive group and from 1.35 ± 0.12 to 1.19 ± 0.21, p = 0.01 in the negative group). The gap of H/CL between highest H/CL of negative case and lowest H/CL of positive case was narrower in 3 h. On the other hand, correlation between H/CL and left ventricular posterior wall thickness tends to be clearer in 3 h (p = 0.12, r = 0.30 for 1 h, p = 0.04, r = 0.39 at 3 h).

Our study suggests that both 1-h and 3-h incubation times for ^99mTc-PYP imaging have different benefits for ATTR cardiac amyloidosis. A one-hour incubation may be preferable for differential diagnostic purposes, while a three-hour incubation may provide greater utility in evaluating disease severity.