Late-breaking abstract: Short term improvement in 6 minute walk distance predicts long term survival in incident idiopathic pulmonary arterial hypertension. Results from the Pulmonary Hypertension Registry of the United Kingdom and Ireland

Background: Improvement in 6 minute walk distance (6MWD) after 12-16 weeks of treatment has been used as the primary end point in many pivotal pulmonary arterial hypertension (PAH) clinical trials. However, the consensus view is that although baseline 6MWD predicts survival, change in 6MWD (Δ6MWD) does not. Aim: To determine whether Δ6MWD after 3 months of disease targeted therapy predicts long term survival in patients from the Pulmonary Hypertension Registry of the UK and Ireland. Methods: Retrospective observational study of all incident cases of idiopathic (IPAH), heritable and anorexigen-associated PAH diagnosed in the UK and Ireland between 1st January 2001 and 31st December 2009. Patients were divided into low and high baseline 6MWD by the median 6MWD (295 m). Results: Total of 646 patients were diagnosed. After 3 months of disease targeted therapy, patients with absolute 6MWD >353 m (corresponding to the median value at 3 months) had better survival than those with 6MWD < 353 m. Mean improvement in 6MWD after 3 months of therapy was 42.4±75.8 m (median 37.5 m). Patients with greater increase in 6MWD from baseline to 3 months had better post-3 months survival (hazard ratio 0.65, 95% confidence interval 0.42 to 0.99 per 100 metres improvement). In patients with low baseline 6MWD, Δ6MWD at 3 months of > 37.5 m had better survival compared to those with Δ6MWD at 3 months of < 37.5 m (Log-rank, p=0.03). This is not seen in patients with high baseline 6MWD. Conclusion: Change in 6MWD after 3 months of treatment predicts long term survival in patients with low baseline 6MWD.