End points in pulmonary arterial hypertension: the way forward

Pulmonary arterial hypertension is a rare disease of poor prognosis. Despite its rarity >1,000 patients have been randomised in placebo-controlled trials using novel therapies, including prostacyclin analogues, endothelin receptor antagonists and, most recently, phosphodiesterase 5 inhibitors. Nearly all of these trials have used exercise capacity, measured by the unencouraged 6-min walking distance, as the primary end point and a variety of other measurements as secondary end points. This approach has been productive, leading to the licensing of a number of effective treatments. Future clinical trials, however, will probably assess drug combinations, make comparisons between drugs and include less severely ill patients. It is, therefore, timely to examine the end points used. The authors discussed the various end points that have been used in the past and possible end points that might be used in the future. End points considered included measurements of: exercise capacity, haemodynamics, quality of life, imaging of the right heart and circulation, and chemical markers of pulmonary hypertension. Many of these show promise but will have to be used in parallel and compared with conventional end points such as the 6-min walking distance before their value can be demonstrated convincingly to the regulatory authorities.