Regional myocardial metabolic rate of oxygen measured by O2-15 inhalation and positron emission tomography in patients with cardiomyopathy

Background: Positron emission tomography (PET) metabolic studies have investigated the pathways involved in fatty acid, glucose, and oxidative metabolism in cardiomyopathy and the impairments that occur in the damaged myocardium, but none have provided absolute quantitative variables. Recently, quantitative measurements of the metabolic rate of oxygen (MMRO2) and oxygen extraction fraction (OEF) using O-2-15-labeled oxygen gas have been validated in animals and healthy volunteers. The purposes of the current study were to measure MMRO2 and OEF in cardiomyopathy with left ventricular (LV) dysfunction. Methods: The authors selected 25 study participants: 16 patients (10 with ischemic and 6 with dilated) cardiomyopathy with LV dysfunction, and 9 healthy volunteers. As evaluated by echocardiography, LV ejection fraction (LVEF) was decreased in patients (35% +/- 9% vs, 65% +/-: 5%, P < 0.01), The PET protocol consisted of transmission, C O-2-15 static, H-2 O-15 dynamic, and O-2-15 gas inhalation steady state scans. An entire myocardial region of interest was drawn to encompass the entire LV myocardium on three midventricular slices in each participant. Results: Data showed in patients with dilated cardiomyopathy significant reductions of MMRO2 (0.051 +/- 0.02 ml(.)min(-1.)g(-1) vs. 0.108 +/- 0.02 ml(.)min(-1.)g(-1), P = 0.01) and OEF (0.55 +/- 0.15 vs. 0.71 +/- 0.08, P = 0.01) when compared with healthy volunteers. Furthermore, OEF decreased significantly in lateral and inferior walls. Significant correlations were observed among OEF and the rate-pressure product (RPP) (P = 0,02), LVEF (P < 0.001), MMRO2 and RPP (P = 0.04), and LVEF (P = 0.05), In patients with ischemic cardiomyopathy, MMRO2 was significantly reduced (0.039 +/- 0.02 ml(.)min(-1.)g(-1) vs. 0.108 +/- 0.02 ml(.)min(-1.)g(-1); P = 0.005) but not OEF (0.63 +/- 0.2 vs 0.71 +/- 0.08; P = NS), when compared with healthy volunteers. Significant correlations were observed among OEF and RPP (P = 0.03), LVEF (P = 0.002), MMRO2 and RPP (P < 0.01), and LVEF (P = 0.03). Conclusions: These data show that O-2-15 gas inhalation and PET allow myocardial MMRO2 and OEF to be measured in patients with cardiomyopathy.