Survival in pulmonary arterial hypertension: a reappraisal of the NIH risk stratification equation

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Abstract
The aim of the present study was to determine contemporary survival in pulmonary arterial hypertension (PAH), and to investigate whether or not the National Institutes of Health (NIH) equation remains an accurate predictor of survival.In 576 patients with PAH referred during 1991–2007, observed survival was described using the Kaplan–Meier method. In patients with idiopathic, familial and anorexigen-associated PAH (n = 247), observedversusNIH equation predicted survival was compared. A new survival prediction equation was developed using exponential regression analysis.The observed 1-, 3- and 5-yr survival in the total cohort were 86, 69 and 61%, respectively. In patients with idiopathic, familial and anorexigen-associated PAH, the observed 1-, 3- and 5-yr survival (92, 75 and 66%, respectively) were significantly higher than the predicted survival (65, 43 and 32%, respectively). The new equation (P(t) = e-A(x,y,z)t, where P(t) is probability of survival,tthe time interval in years, A(x,y,z) = e(−1.270–0.0148x+0.0402y–0.361z),xthe mean pulmonary artery pressure,ythe mean right atrial pressure andzthe cardiac index) performed well when applied to published contemporary studies of survival in PAH.Contemporary survival in the PAH cohort was better than that predicted by the NIH registry equation. The NIH equation underestimated survival in idiopathic, familial and anorexigen-associated PAH. Once prospectively validated, the new equation may be used to determine prognosis.