Inter-observer reproducibility and intra-observer repeatability in ^99mTc-pyrophosphate scan interpretation for diagnosis of transthyretin cardiac amyloidosis

Aim: The purpose of this study was to determine the inter- and intra-observer variability in ^99mtechnetium-pyrophosphate (^99mTc-PYP) scan interpretation for diagnosis of transthyretin cardiac amyloidosis (ATTR).

Methods and results: Our study cohort comprised 100 consecutive subjects referred for ^99mTc-PYP imaging based on clinical suspicion of ATTR cardiac amyloidosis. Myocardial ^99mTc-PYP uptake was assessed by both visual (comparison of myocardial to rib uptake) and semi-quantitative (heart-to-contralateral lung uptake ratio, H:CL) methods. Twenty scans were analyzed twice, at least 48 hours apart, by each of two independent observers. Patients with visual scores of ≥ 2 on planar imaging as well as myocardial uptake on SPECT/CT were classified as ATTR positive. Diagnosis of ATTR by visual ^99mTc-PYP grade was perfectly reproducible [concordance: positive and negative scans 100% (53/53 and 47/47, respectively). Both inter- and intra-observer correlations for H:CL ratio (r² = 0.90, 0.99 (Observer 1) and 0.98 (Observer 2), respectively) and repeatability values on Bland-Altman plots were excellent. The coefficient of variation (%) for Observers 1 and 2 was 3.21 (2.14 to 4.29) and 7.49 (4.95 to 10.09), respectively. In addition, there was 100% concordance in positive and negative scan interpretation by visual grading between novice CV imagers (< 3 years' experience) and an experienced CV imager (10 years' experience).

Conclusions: This study showed excellent inter-observer reproducibility and intra-observer repeatability of ^99mTc-PYP visual scan interpretation and H:CL ratio for diagnosis of cardiac ATTR amyloidosis. Cardiac ATTR amyloidosis can be diagnosed reliably using ^99mTc-PYP SPECT/CT by novice and experienced CV imagers.