Comparison of planar with tomographic pyrophosphate scintigraphy for transthyretin cardiac amyloidosis: Perils and pitfalls

Background Tc-99m pyrophosphate (PYP) SPECT is recommended for indeterminate findings on planar imaging. We aimed to compare the findings on planar PYP scintigraphy alone to that of routinely performed PYP SPECT. Methods PYP scintigraphy data of 133 patients (53% men; mean age 76 years) were evaluated. SPECT was routinely performed following 1-hour planar imaging, in all cases. Semiquantitative visual score and heart-to-contralateral (H/CL) ratio were determined in all patients as recommended. Results PYP images from 35 patients (26%) were considered to be positive based on SPECT myocardial uptake. Among them, 20 (57%) had a H/CL ratio >= 1.5 and 34 had a visual score >= 2. SPECT identified myocardial uptake in one patient with a visual score < 2 and refuted the presence of myocardial uptake in two patients with a visual score >= 2. Visual score correlated well with SPECT (r= 0.94;P< .0001) and had an accuracy of 98% for tomographic myocardial uptake. Addition of H/CL ratio reduced the diagnostic performance of visual score. Conclusions Planar-derived visual score has an excellent accuracy for tomographic myocardial uptake, though it misclassifies a small proportion of patients. H/CL ratio decreases the diagnostic certainty of planar imaging. Tomographic imaging prevents misdiagnoses and should always be performed.