Background
18F-florbetapir is a promising imaging biomarker for light chain (AL) and transthyretin (ATTR) cardiac amyloidosis. Our aim, using human autopsy myocardial specimens, was to test the hypothesis that 18F-florbetapir binds specifically to myocardial AL and ATTR amyloid deposits.
Methods and Results
We studied myocardial sections from 30 subjects with autopsy documented AL (N = 10), ATTR (N = 10) and non-amyloid controls (N = 10), using 18F-florbetapir and cold florbetapir compound and digital autoradiography. Total and non-specific binding of 18F-florbetapir was determined using the maximum signal intensity values. Specific binding of 18F-florbetapir was calculated by subtracting non-specific from total binding measurements (in decays per minute/mm2, DPM mm2), and was compared to cardiac structure and function on echocardiography and the histological extent of amyloid deposits. Diffuse or focally increased 18F-florbetapir uptake was noted in all AL and ATTR samples and in none of the control samples. Compared to control samples, mean 18F-florbetapir specific uptake was significantly higher in the amyloid samples (0.94 ± 0.43 vs. 2.00 ± 0.58 DPM/mm2, p < 0.001), and in the AL compared to the ATTR samples (2.48 ± 0.40 vs. 1.52 ± 0.22 DPM/mm2, p < 0.001). The samples from subjects with atypical echocardiographic features of amyloidosis showed quantitatively more intense 18F-florbetapir specific uptake compared to control samples (1.50 ± 0.17 vs. 0.94 ± 0.43 DPM/mm2, p = 0.004), despite smaller amyloid extent than in subjects with typical echocardiograms.
Conclusions
18F-florbetapir specifically binds to myocardial AL and ATTR deposits in humans and offers the potential to screen for the two most common types of myocardial amyloid.