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Myocardial Viability Assessment by PET: ⁸²Rb Defect Washout Does Not Predict the Results of Metabolic–Perfusion Mismatch

¹ Carlyle Fraser Heart Center, Emory Crawford Long Hospital, Division of Cardiology, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia
² Department of Radiology, Emory University School of Medicine, Atlanta, Georgia

PET is a sensitive technique for the identification of viable myocardial tissue in patients with coronary disease. Metabolic assessment with ¹⁸F-FDG is considered the gold standard for assessment of viability before surgical revascularization. Prior research has suggested that viability may be assessed with washout of ⁸²Rb between early and late resting images. Our objective was to determine whether assessment of myocardial viability with ⁸²Rb washout is reliable when compared with PET using ¹⁸F-FDG. Methods: We performed PET for 194 patients referred for PET ¹⁸F-FDG/⁸²Rb to assess viability for clinical indications. We included 151 patients with resting defects >10% of the left ventricle (LV) (n = 159 defects). Patients with smaller resting ⁸²Rb defects (<10% LV) were excluded for the purpose of this study. PET images acquired with ⁸²Rb and ¹⁸F-FDG defined viability by the mismatch between metabolism and perfusion (¹⁸F-FDG >125% of ⁸²Rb uptake in the ⁸²Rb defect). Evidence of viability with ⁸²Rb was assessed by the presence of (i) severity: ⁸²Rb counts in the defect >50% of ⁸²Rb in the normal zone of the resting PET images; (ii) washout: decrease of ⁸²Rb counts in the defect from early to late resting ⁸²Rb images <17% between the first 90-s image and the final 300-s image; or (iii) combined severity and washout criteria, which required positive criteria for (i) and (ii) to indicate viability. Results: Prevalence of viability by ¹⁸F-FDG/⁸²Rb criteria was 50% (n = 79). Severity criteria yielded a sensitivity of 76% and a specificity of 17%, washout criteria yielded a sensitivity of 81% and a specificity of 23%, and both criteria had a sensitivity of 63% and a specificity of 32%. Positive and negative predictive values were poor for all criteria. No correlation existed between ⁸²Rb washout and ¹⁸F-FDG–⁸²Rb mismatch (r² = 0.00). Multiple receiver-operating-characteristic plots showed very poor discrimination despite varying criteria for viability by ⁸²Rb (severity from 50% to 60% of normal zone, washout from 12% to 17%). Conclusion: ⁸²Rb washout from early to late resting images, combined with quantitative severity of the resting ⁸²Rb defect, did not yield results equivalent to PET ¹⁸F-FDG–⁸²Rb mismatch and may not accurately assess myocardial viability.

Key Words: myocardial viability • ⁸²Rb • PET • coronary artery disease • myocardial perfusion imaging

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