Mixed Venous Oxygen Saturation Is a Better Prognosticator Than Cardiac Index in Pulmonary Arterial Hypertension.

Abstract

European Society of Cardiology (ESC) and European Respiratory Society (ERS) guidelines include thermodilution cardiac index (TDCI) and mixed venous oxygen saturation (SvO₂) as two of the three hemodynamic determinations used in risk assessment of patients with pulmonary arterial hypertension (PAH). SvO₂ may be a better measurement than TDCI to assess prognosis in patients with either idiopathic or heritable PAH. What is the concordance between TDCI and SvO₂ ESC/ERS risk group allocation and their prognostic value in patients with PAH? In this retrospective study, we assessed the correlation between SvO₂ and TDCI in patients with idiopathic and heritable PAH. We determined concordance in the ESC/ERS risk group allocation and association with survival, both at baseline and follow-up. A total of 158 patients (mean age, 58 ± 17 years; 72% women) with idiopathic (91%) and heritable (9%) PAH were included. There was moderate association between TDCI and SvO₂ (r = 0.50; 95% CI, 0.37-0.62). Weighted kappa revealed a fair agreement between TDCI and SvO₂ (κ = 0.30; 95% CI, 0.18-0.42), with concordance in risk group allocation in 49% of patients. During a median follow-up of 45 months (interquartile range, 23-105), 62 patients (39%) died. Using Kaplan-Meier analysis, survival was impacted by the SvO₂ (log rank = 0.002) but not by the TDCI risk group allocation (log-rank = 0.51). Using the Cox proportional hazard model, adjusted for age and sex, SvO₂ (but not TDCI) was associated with mortality (hazard ratio per 1% change, 0.94; 95% CI, 0.91-0.97; P < .001). When using the cutoffs proposed by the ESC/ERS guidelines, we noted poor concordance in risk score allocation between TDCI and SvO₂. In patients with idiopathic or heritable PAH, SvO₂ measurements are superior to TDCI in predicting long-term mortality.