Right ventricular failure in idiopathic pulmonary arterial hypertension is associated with inefficient myocardial oxygen utilization

Abstract

Background - In idiopathic pulmonary arterial hypertension (IPAH), increased right ventricular (RV) power is required to maintain cardiac output. For this, RV O 2 consumption (MVO 2) must increase by augmentation of O 2 supply and/or improvement of mechanical efficiency-ratio of power output to MVO 2. In IPAH with overt RV failure, however, there is evidence that O 2 supply (perfusion) reserve is reduced, leaving only increase in either O 2 extraction or mechanical efficiency as compensatory mechanisms. We related RV mechanical efficiency to clinical and hemodynamic parameters of RV function in patients with IPAH and associated it with glucose metabolism. Methods and Results - The patients included were in New York Heart Association (NYHA) class II (n=8) and class III (n=8). They underwent right heart catheterization, MRI, and H 215O-, 15O 2-, C 15O-, and 18FDG-PET. RV power and O 2 supply were similar in both groups (NYHA class II versus class III: 0.54±0.14 versus 0.47±0.12 J/s and 0.109±0.022 versus 0.128±0.026 mL O 2/min per gram, respectively). RV O 2 extraction was near-significantly lower in NYHA class II compared with NYHA class III (63±17% versus 75±16%, respectively, P=0.10). As a result, MVO 2 was significantly lower (0.066±0.012 versus 0.092±0.010 mL O 2/min per gram, respectively, P=0.006). RV efficiency was reduced in NYHA class III (13.9±3.8%) compared with NYHA class II (27.8±7.6%, P=0.001). Septal bowing, measured by MRI, correlated with RV efficiency (r=-0.59, P=0.020). No relation was found between RV efficiency and glucose uptake rate. RV mechanical efficiency and ejection fraction were closely related (r=0.81, P=0.001). Conclusions - RV failure in IPAH was associated with reduced mechanical efficiency that was partially explained by RV mechanical dysfunction but not by a metabolic shift. © 2011 American Heart Association, Inc.