Comparative Prognostic and Diagnostic Value of Myocardial Blood Flow and Myocardial Flow Reserve After Cardiac Transplantation.

Abstract

Cardiac allograft vasculopathy (CAV) is a major cause of graft failure after cardiac transplantation. CAV is characterized by diffuse involvement of epicardial coronary arteries and the microvasculature. PET allows quantification of absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR), which may be accurate markers of CAV severity. We compared the diagnostic and prognostic utility of stress MBF and MFR after cardiac transplantation. <b>Methods:</b> This was a cohort study of consecutive cardiac transplant patients undergoing ⁸²Rb PET scans. Semiquantitative regional analysis and global measurement of stress MBF and MFR were performed. Associations with all-cause mortality were assessed with multivariable Cox analysis. The diagnostic accuracy for significant CAV (grade 2/3) and the prognostic accuracy of stress MBF and MFR, corrected and uncorrected for rate-pressure product, were compared. <b>Results:</b> In total, 99 patients, mean age 68.8 y and 75.8% male, were followed for a median of 3.4 y, during which 26 deaths occurred. Stress MBF and MFR had similar diagnostic accuracy for significant CAV. However, uncorrected MFR had improved discrimination for all-cause mortality compared with stress MBF (area under the curve, 0.748 vs. 0.639; <i>P</i> = 0.048). Higher MFR (adjusted hazard ratio, 0.30; <i>P</i> < 0.001), but not stress MBF (adjusted hazard ratio, 1.14; <i>P</i> = 0. 656), was associated with reduced all-cause mortality. Preserved MFR (>2.0) identified relatively low-risk patients (annual mortality, 4.7%), whereas the presence of a left ventricular ejection fraction lower than 45% and MFR lower than 1.7 identified high-risk patients (annual mortality, 51.6%). <b>Conclusion:</b> Quantitative PET analysis, and particularly MFR, has diagnostic and prognostic utility after heart transplantation. Preserved MFR identifies low-risk patients, whereas the presence of multiple abnormal parameters identifies high-risk patients.