Right Ventricular Bone-Avid Tracer Uptake: A Novel Risk Marker in Transthyretin Amyloid Cardiomyopathy

Single photon emission computed tomography (SPECT) using bone-avid tracers such as technetium-99m-labeled pyrophosphate (PYP), 99mTc-3,3-diphosphono-1,2-pyrophosphate (DPD), or 99mTc-hydroxymethylene diphosphonate (HMDP) is a well-established noninvasive method for diagnosing transthyretin amyloid cardiomyopathy (ATTR-CM).Extensive data from thousands of patients confirms its high accuracy in diagnosing ATTR-CM in those who are symptomatic.1 Recent studies also indicate its utility in screening for amyloidosis in individuals at risk, such as those with carpal tunnel syndrome.The prognostic value of 99mTc-PYP/DPD/HMDP myocardial uptake in ATTR-CM has been summarized in a prior review article. 2 Many of these studies evaluated visual grade as well as semiquantitative measures on planar images. 2 Patients with negative scans (no myocardial uptake, grade 0) have shown significantly better survival rates compared to those with positive scans (myocardial uptake less than bone, equal to bone or greater than bone uptake, grades 1, 2, or 3, respectively). 2 However, among patients with positive scans, there is no difference in survival rates between those with grades 1, 2, or 3 uptake.2 Semi-quantitative measures, such as the heart to contralateral lung ratio (H:CL ratio > 1.6) and heart to whole body ratio (H:WB > 7.5) derived from planar imaging, have also been shown to be poor prognostic markers. 2 Data evaluating right ventricular (RV) uptake on 99mTc-PYP/DPD/HMDP SPECT are limited.Distinction between left ventricular (LV) and right ventricular (RV) myocardial uptake is not feasible on planar images and SPECT is needed.In this issue, the study conducted by Porcari A et al. 3 evaluated RV uptake on 99mTc-PYP/DPD/HMDP SPECT images of patients diagnosed with ATTR-CM, and determined its prognostic significance.This retrospective analysis involved 1422 patients diagnosed with ATTR-CM based on standard criteria from five centers, including the National Amyloidosis Center (NAC) in the UK and four Italian centers.TTR genotyping was performed in all patients.RV uptake was classified on SPECT images as either focal, limited to the basal RV