Serial scanning with technetium pyrophosphate (^99mTc-PYP) in advanced ATTR cardiac amyloidosis

Background: Development of noninvasive imaging modalities to quantify amyloid burden over time is an unmet clinical need. Technetium pyrophosphate (^99mTc-PYP) scintigraphy is a simple and widely available radiotracer useful to differentiate transthyretin from light-chain amyloidosis in patients with advanced cardiac amyloidosis. We examined the utility of serial ^99mTc-PYP scanning to quantify amyloid burden over time in TTR cardiac amyloidosis (ATTR-CA). Methods and Results: Twenty subjects with ATTR-CA (10 wild type, 10 mutant) underwent serial ^99mTc-PYP planar cardiac imaging. Cardiac retention was assessed both semiquantitatively (visual score 0, no uptake to 3, uptake greater than bone) and quantitatively (region of interest drawn over the heart, copied, and mirrored over the contralateral chest) to calculate a heart-to-contralateral (H/CL) ratio. Index scan mean visual score and H/CL were 3.0 ± 0.2 and 1.79 ± 0.2, respectively, and after an average 1.5 ± 0.5 years follow-up, did not differ, 3.0 ± 0.2, P = .33 and 1.76 ± 0.2, P = .44. H/CL change was minimal, 0.03 ± 0.17, did not correlate with time between scans, r = 0.19, P = .43, and was observed despite obvious clinical progression (increase in troponin ≥ 0.1 ng/mL, BNP ≥ 400 pg/mL, NYHA class, and/or death). Conclusions: Serial ^99mTc-PYP scanning in subjects with advanced ATTR-CA does not show significant changes over an average 1.5 years of follow-up despite obvious clinical progression.