Fig. 1

Patient Selection. Patient data were extracted from two MarketScan databases. The index date was defined as the first claim for ICD-9-CM code 416.0 (primary pulmonary hypertension) or 416.8 (other chronic pulmonary heart disease). The baseline and follow-up periods consisted of the 12 months pre- and post-index date. Patients underwent two matching procedures: case and control patients were pre-matched by age, sex, region, and plan type and subsequently matched on lung disease(s) from the pre-matched patient pool. ICD-9–CM = International Classification of Diseases, Ninth Revision, Clinical Modification; PH = pulmonary hypertension; RHC = right heart catheterization; WHO = World Health Organization