11C-Acetate clearance as an index of oxygen consumption of the right myocardium in idiopathic pulmonary arterial hypertension: a validation study using 15O-labeled tracers and PET.

Abstract

Idiopathic pulmonary arterial hypertension (IPAH) results in increased right ventricular (RV) workload and oxygen demand. It has been shown that myocardial oxygen consumption (MVO2) of the hypertrophied right ventricle of IPAH patients can be measured using PET and (15)O-labeled tracers. This method is, however, not very suitable for routine clinical practice. The purpose of the present study was to assess whether MVO2 can also be determined in the right ventricle of IPAH patients from the clearance of (11)C-acetate, a simple method that is in use for MVO2 measurements of the left myocardium. Seventeen of 26 IPAH patients performed the total PET study. Nine other patients were scanned only for (11)C-acetate. (15)O-H2O, (15)O-O2, and (15)O-CO scans were used to derive RV flow, oxygen extraction fraction, and blood volume, respectively, from which RV MVO2 was calculated. The rate of clearance determined by monoexponential curve fitting (K(mono)) and the efflux rate constant k2 were derived from the (11)C-acetate scan. The RV rate-pressure product was also determined by means of right heart catheterization, as an index of the RV MVO2, and was calculated as the product of systolic pulmonary artery pressure and heart rate. Both (11)C-acetate clearance rates, K(mono) (R(2) = 0.41, P = 0.006) and k2 (R(2) = 0.45, P = 0.003), correlated with RV MVO2. They also correlated with RV rate-pressure product (K(mono), R(2) = 0.41, P = 0.0005; k2, R(2) = 0.48, P < 0.0001). (11)C-acetate clearance rates correlated moderately with quantitative RV MVO2 measurements in IPAH. Therefore, (11)C-acetate PET can be used only as an index of RV oxidative metabolism in IPAH patients.