Relationship of Pulmonary Arterial Capacitance and Mortality in Idiopathic Pulmonary Arterial Hypertension

OBJECTIVES: The purpose of this study was to determine if pulmonary vascular capacitance predicts survival in patients with idiopathic pulmonary arterial hypertension (IPAH). BACKGROUND: The prognosis of patients with IPAH is difficult to predict, despite knowledge of clinical and hemodynamic parameters previously identified as predictors. METHODS: We proposed a capacitance index of stroke volume divided by pulmonary pulse pressure (SV/PP) and prospectively gathered data on IPAH patients who underwent a right heart catheterization. SV/PP was analyzed as a predictor of mortality after adjusting for other modifiers of risk. RESULTS: During 4-year follow-up of 104 patients, 21 patients died. When compared with conventional markers, SV/PP was the strongest univariate predictor of mortality (hazard ratio 17.0 per ml.mm Hg(-1) decrease, 95% confidence interval 13.0 to 22.0; p < 0.0001). In successive bivariate analysis, SV/PP was the only predictor of mortality. In quartile analysis, the lowest SV/PP quartile had a 4-year mortality of 61%; the highest SV/PP had no deaths. CONCLUSIONS: The capacitance index (SV/PP) is a strong independent predictor of mortality in patients with IPAH.