In pulmonary arterial hypertension (PAH) the right ventricle (RV) is exposed to a high afterload and is hypertrophied. It is postulated that this hypertrophy forces the RV to increase the myocardial glucose uptake rate (MRglu). It has been shown that a higher right to left ventricle ratio (RV/LV-ratio) of MRglu in PAH is associated with more severe disease. However, there is contradicting evidence whether this increased ratio is a result from increased RV or reduced LV uptake. Also, metabolic alterations in the interventricular septum are unknown.Therefore we aimed to investigate the cause of changing MRglu RV/LV-ratio in PAH, the role of the septum, and the role of hypertrophy in this process.Methods
Seventeen idiopathic PAH patients underwent an [18F]-Fluordeoxyglucose PETscan to measure MRglu. Additionally, cardiac magnetic resonance imaging and right heart catheterisation were performed to determine RV function.Results
Higher MRglu RV/LV-ratio was mainly determined by reduced LV uptake rather than increased RV uptake (RV/LV < 1: LV 0.36 ± 0.09 vs RV 0.24 ± 0.08 µmol/g/min, p=0.001; RV/LV > 1: LV 0.25 ± 0.05 vs RV 0.29 ± 0.05 µmol/g/min, p=0.35) (figure). The septum MRglu correlated positively with LV MRglu (r=0.82, p < 0.001), but not with RV MRglu (r=0.29,p=0.25). RV/LV-ratio correlated strongly with RV function parameters: RV ejection fraction r=-0.51, p=0.04; mean pulmonary artery pressure r=0.58, p=0.02;and pulmonary vascular resistance r=0.61, p < 0.01. In addition, both LV and RV MRglu correlated positively with LV and RV mass respectively (LV r=0.47, p < 0.05; RV r=0.80, p=0.0001).Conclusion
Increased RV/LV-ratio is determined by decreasing LV MRglu and is associated with more severe PAH. Furthermore, low LV MRglu reflects decreasing LVmass or atrophy and is accompanied by lower septum MRglu.