Accurate assessment of load-independent right ventricular systolic function in patients with pulmonary hypertension

Background: End-systolic elastance (E_es), a load-independent measure of ventricular function, is of clinical interest for studies of the right ventricle (RV) in patients with pulmonary arterial hypertension (PAH). The objective of this study was to determine whether, in PAH patients, E _es can be estimated from mean pulmonary artery pressure (mPAP) and end-systolic volume (ESV) only. Methods: Right heart catheterization was used to measure mPAP. Maximal isovolumic pressure (P_iso) was estimated from RV pressure curves with the so-called single-beat method. Cardiac magnetic resonance imaging (MRI) was used to assess RV end-diastolic and end-systolic volumes (EDV and ESV). E_es was then calculated as: E_es = (P_iso-mPAP) / (EDV-ESV), and as E_{es,V0 = 0} = mPAP/ESV (simplified method, with V0 = 0, is negligible volume at zero pressure). Right ventricular volume at zero pressure (V₀) was then defined as the intercept of the end-systolic pressure-volume relation (single-beat method) with the horizontal axis. Results: E_{es,V0 = 0} was significantly lower compared with E_es (0.61 vs 1.34 mm Hg/ml, respectively, p<0.01). A modified Bland-Altman analysis showed a contractility-dependent difference between E_{es,V0 = 0} and E_es. Moreover, V₀ ranged from-8 up to 171 ml, and a moderate and good correlation was found between V₀ and EDV, and V₀ and ESV, respectively (r = 0.65 and r = 0.87, p< 0.01). Conclusions: These findings show that V₀ is dependent on RV dilation. Therefore, the assumption that V₀ is negligible in PAH is incorrect. Consequently, for an accurate assessment of load-independent RV systolic function, RV volumes and pressure curves are required.