Measurement of myocardial glucose uptake in patients with ischemic cardiomyopathy: Application of a new quantitative method using regional tracer kinetic information

Quantification of myocardial glucose uptake (MGU) by F-18-fluoro-2-deoxyglu cose (FDG) using PET may be inaccurate, because the correction factor that relates myocardial FDG uptake to MGU, the lumped constant (LC), is not a tr ue constant. Recent studies have shown that analysis of FDG time-activity c urves allows determination of individual LCs and that variable LCs yield ac curate determination of MGU. We compared the magnitude of the LC in differe nt regions of the heart in patients with ischemic cardiomyopathy. Methods: Twenty patients with ischemic cardiomyopathy and an average ejection fracti on of 33% underwent dynamic N-13-ammonia and FDG PET. We determined myocard ial perfusion and MGU in 177 regions classified as control (71 regions), mi smatch (50 regions) and match (56 regions), according to findings on PET an d echocardiography. Regional MGU was calculated with both regional LCs and a fixed LC of 0.67. Results: All results were expressed as mean +/- SD. Myo cardial perfusion was highest in control regions (0.52 +/- 0.18 ml/g/min), reduced in mismatch regions (0.43 +/- 0.19 mL.g/min; P< 0.05 versus control ) and severely reduced in match regions (0.28 +/- 0.17 mL/g/min; P < 0.001 versus control and mismatch). Regional LCs ranged from 0.45 to 1.30 and dif fered between patients (P < 0.001). Regional LCs were similar in regions di agnosed as control (0.78 +/- 0.23), mismatch (0.80 +/- 0.24) and match (0.7 2 +/- 0.21). MGU (mu mol/g/min) calculated by regional LCs was similar in c ontrol (0.52 +/- 0.16) and mismatch (0.49 +/- 0.19) regions and decreased i n match regions(0.31 +/- 0.12, P< 0.001). The agreement between MGU calcula ted with variable and fixed LCs was poor. Conclusion: The LC used in the ca lculation of MGU was not affected by regional differences in the metabolic state of the myocardium. However, the LC varied substantially between patie nts in control, mismatch and match regions. These findings indicate that qu antitative measurements of MGU using a fixed LC must be interpreted with ca ution.