Background: Right ventricular (RV) function is a major determinant of survival in patients with pulmonary arterial hypertension (PAH). Hemodynamic parameters like end-systolic elastance (Ees), arterial elastance (Ea), Ees/Ea ratio or pulmonary arterial compliance (PAC) have been shown to reflect RV function and prognosis in PAH. Increased RV 18F-fluoro-2-deoxyglucose (FDG) uptake in positron emission tomography (PET) was recently connected with progressive RV dysfunction in these patients. In our pilot study we aimed to compare novel parameters of RV function from right heart catheterization (RHC) and magnetic resonance imaging (MRI) with PET-derived FDG uptake.
Methods and results: Twenty stable PAH patients (age 50.05±16.51 years) with mean pulmonary artery pressure (mPAP)
48.95±18.77 mmHg had simultaneous PET/MRI scans performed. FDG was used as a tracer and its uptake was presented as a standardized uptake value (SUV) for both left (LV) and right ventricle. Mean SUV RV/SUV LV ratio was 0.97±0.63. SUV RV/SUV LV ratio significantly correlated with pulmonary vascular resistance (PVR) (r=0.75, p<0.0001), mPAP (r=0.82, p=0.0001), Ees/Ea ratio (estimated by stroke volume (SV)/end-diastolic volume (ESV) ratio) (r=-0.69, p=0.001), estimated Ea (r=0.7089, p<0.0001); estimated Ees (r=0.493, p=0.03); RV stroke work index (r=0.82, p<0.0001) and PAC (r=-0.77, p<0.0001). Patients with mPAP value higher than 35 mmHg presented higher SUV RV/SUV LV ratio (1.28 vs 0.38, p<0.0001), Ea (0.76±0.22 vs 0.27±0.05, p<0.0001), Ees (0.51±0.17 vs 0.29±0.08, p=0.001) and lower SV/ESV ratio (0.69±0.15 vs 1.07±0.23, p=0.001). Using ROC analysis we obtained a cut-off value for SUV RV/SUV LV ratio. Patients with SUV RV/SUV LV ratio >0.94 presented lower SV/ESV ratio (0.66±0.13 vs 0.99±0.15, p=0.001) and higher PVR (13.19±4.03 Wood units vs 5.16±2.08 Wood units, p=0.0003) and mPAP (63.4±14.1 mmHg vs 34.5±9.14 mmHg, p<0.0001) than those with ratio <0.94.
Conclusion: Impaired RV function, assessed in MRI and RHC is associated with increased myocytes' glucose uptake visualized by FDG PET. PET/MRI hybrid could provide insights into right ventricle hemodynamic and metabolic function in PAH patients, however its usefulness in diagnostic or therapeutic processes requires further investigations.