Nuclear imaging and echocardiographic findings in hypertrophic cardiomyopathy with and without ATTR‐CM

Abstract Aims Patients with transthyretin amyloid cardiomyopathy (ATTR‐CM) often experience delayed diagnosis, which may detrimentally impact clinical outcomes. This study aimed to assess the frequency of use of planar scintigraphy with and without single‐photon emission computed tomography (SPECT) in patients with hypertrophic cardiomyopathy (HCM) screened for ATTR‐CM in the TTRACK study. Variability in readings based on different readers, tests and radiotracers used in cardiac nuclear imaging, and differences in echocardiogram findings between patients with and without ATTR‐CM were explored. Methods Patients aged ≥50 years with HCM (left‐ventricular wall thickness ≥15 mm without an identified cause) underwent diagnostic technetium‐99m 99m TcTc‐DPD 3,3‐diphosphono‐1,2‐propanodicarboxylic acid, ‐PYP pyrophosphate and ‐HMDP hydroxymethylene diphosphonate–labelled planar bone scintigraphy with or without SPECT. Cardiac‐versus‐bone uptake on images was visually graded (Perugini, 0–3) by onsite and central readers (discrepancies resolved by consensus). Patients with grade 1–3 cardiac uptake underwent monoclonal protein testing. Results Of 766 eligible patients (mean age ± standard deviation, 72.3 ± 10.6 years, 69.6% male), 691 (90.2%) had planar imaging alone and 75 (9.8%) planar plus SPECT imaging. Cardiac uptake was observed on imaging in 245 patients (32.0%); grades 1, 2 and 3 were assigned in 37 (4.8%), 34 (4.4%) and 174 (22.7%), respectively. Initial cardiac uptake grading for planar scintigraphy by onsite readers was strongly concordant with consensus decisions κ coefficient, 0.84 (95% confidence interval 0.81–0.88). Grading for planar versus SPECT imaging was very strongly concordant 0.93 (95% confidence interval 0.86–1.00); discordant findings were only observed with 99m TcTc‐PYP. Compared with patients with no cardiac uptake, patients with ATTR‐CM had a lower mean left ventricular (LV) ejection fraction (55.7% vs. 61.4%; P < 0.001), higher mean LV mass index (179.0 vs. 155.6 g/m 2 ; P < 0.01), a higher rate of preserved apical strain (73.4% vs. 57.9%; P < 0.05) and differences in hypertrophic pattern ( P < 0.001), such as a higher rate of concentric hypertrophic pattern (77.5% vs. 38.8%;). Clinical overlap between patients with ATTR‐CM and those without cardiac uptake was high. Conclusions In this real‐world study, a high level of concordance was seen in cardiac uptake grading on planar versus SPECT imaging, with discordant findings only observed with 99m TcTc‐PYP. The findings support the use of these imaging tools to facilitate ATTR‐CM screening in clinical practice. Further studies should investigate differences across tracers used in ATTR‐CM screening. NCT03842163.