Validation of the pulmonary hypertension connection equation for survival prediction in pulmonary arterial hypertension

Objective: The pulmonary hypertension connection (PHC) equation predicts contemporary survival in idiopathic, heritable, and anorexigen-associated pulmonary arterial hypertension (PAH). The aim of this study is to validate the PHC equation in a prospective PAH population cohort and compare its predictability with the French equation. Methods: We compared the rates of actual survival in patients prospectively followed for up to 3.5 years in four double-blind, randomized trials and their open-label extension studies with predicted survival calculated using the PHC equation [(P(t) = e ^(-A(x,y,z)t), A(x,y,z) = e ^{(-1.270-0.0148x + 0.0402y - 0.361z)}, where P(t) is the probability of survival, t the time interval in years, x the mean pulmonary artery pressure, y the mean right atrial pressure, and z the cardiac index] and the French equation in patients with idiopathic, heritable, and anorexigen-associated PAH (n = 449). Results: Mean age was 44 ± 15 years, 77% were women, and 80% had World Health Organization (WHO) functional class III/IV symptoms. The mean 6-min walk distance (6MWD) was 354 ± 95 m. The baseline hemodynamics were as follows: mean right atrial pressure 10 ± 6 mm Hg, mean pulmonary artery pressure 59 ± 15 mm Hg, and cardiac output 4.1 ± 1.5 L/min. The 1-, 2-, and 3-year Kaplan-Meier survival rates were 89%, 80%, and 70%, respectively;the nonadjusted survival rates were 91%, 87%, and 84%, respectively. The expected survival predicted by both the PHC and the French equations was similar to the actual observed Kaplan-Meier survival and was within its 95% confidence limits. The PHC equation also performed well when used in patients with WHO functional class III/IV, cardiac output <4 L/min, or 6MWD <380 m. Conclusion: Risk prediction equations (PHC and French) accurately predicted survival and may be useful for risk estimation in patients with idiopathic, heritable, and anorexigen-associated PAH in large cohort studies. Their use for survival prediction for individual patients needs further study.