Definition, epidemiology and registries of pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a subcategory of pulmonary hypertension (PH) that comprises a group of disorders with similar pulmonary vascular pathology. Though PH is common, the estimated incidence of IPAH is 1–3 cases per million, making it a rare disease. The hemodynamic definition of PAH is a mean pulmonary artery pressure at rest >OR = 25 mm Hg in the presence of a pulmonary capillary wedge pressure <OR = 15 mmHg with pulmonary vascular resistance (PVR) greater than 3 WU. Specific maneuvers during right heart catheterization can be utilized to disclose vasoreactivity and heart failure with preserved ejection fraction, which have implications for management. The inherent complexity in studying a rare disease that exhibits clinical overlap with a common syndrome necessitated the creation of registries. These registries have been indispensable in the characterization and mapping of the natural history of the disease. Equations and risk calculators derived from registries have given clinicians a basis for risk stratification and prognostication. The sequential accumulation of data since the registries began in the 1980s allows for comparisons to be made. Patients who are differentiated by treatment eras and environments can be contrasted. Variability among inclusion criteria similarly allows for comparisons of these subpopulations. This article provides an overview of available registries, highlights insights provided by each and discusses key issues around the interpretation and extrapolation of data from PAH registries. Registries have allowed us to appreciate the improvement in survival afforded by modern therapy and enhanced detection of this disease. Moving forward, a more global approach to registries is needed, as is enhanced collaboration and centralization.