Right Ventricular Myocardial Metabolism and Cardiorespiratory Testing in Patients with Idiopathic Pulmonary Arterial Hypertension.

Background: Non-invasive diagnostic tools for the assessment of pulmonary arterial hypertension (PAH) are currently being intensively studied. Positron emission tomography (PET)/computed tomography (CT) with [18F]-fluorodeoxyglucose ([18F]-FDG) and [13N]-ammonia is the gold standard for assessing myocardial metabolism and perfusion. The relationship between right ventricle (RV) myocardial metabolism and perfusion and cardiopulmonary exercise testing (CPET) has not been studied. Objective: to evaluate correlations between the CPET parameters and RV perfusion and metabolism in IPAH patients. Methods: The study comprised 34 IPAH patients (34.2 ± 8.9 years, 4 males, 6 prevalent). Myocardial metabolism and perfusion were assessed using PET/CT with [18F]-FDG and [13N]-ammonia, respectively. CPET, cardiac MRI and invasive hemodynamics were also evaluated. Results: Significant negative correlations were registered between [18F]-FDG and [13N]-ammonia uptake by the RV (SUVmax _RV/LV) and the oxygen consumption, oxygen pulse and positive correlation with the ratio of minute ventilation to carbon dioxide production. The low-risk IPAH patients significantly differed from the intermediate-to-high-risk group in CPET indices and in SUVmax _RV/LV metabolism and SUVmax _RV/LV perfusion parameters. No reliable differences in CPET indices and [18F]-FDG and [13N]-ammonia uptake by the RV were registered between intermediate- and high-risk patients. Conclusions: CPET is a reliable non-invasive diagnostic tool that could distinguish low-risk young IPAH patients without comorbidities from those at intermediate-to-high risk. Significant correlations between CPET parameters and RV myocardial metabolism and perfusion indices, MRI, and invasive hemodynamics confirm the high diagnostic value for CPET.