Editorials

Pulmonary Hypertension Trials: Current End Points Are Flawed, But What Are the Alternatives?

To ensure effective monitoring of pulmonary arterial hypertension (PAH), a simple, reliable assessment of exercise capacity applicable over a range of disease severity is needed. The aim of this study was to assess the ability of the incremental shuttle walk test (ISWT) to correlate with disease severity, measure sensitivity to change, and predict survival in PAH.

We enrolled 418 treatment-naïve patients with PAH with baseline ISWT within 3 months of cardiac catheterization. Clinical validity and prognostic value of ISWT distance were assessed at baseline and 1 year.

ISWT distance was found to correlate at baseline with World Health Organization functional class, Borg score, and hemodynamics without a ceiling effect (all p < 0.001). Walking distance at baseline and after treatment predicted survival; the area under the receiver operating characteristic curve for ability of ISWT distance to predict mortality was 0.655 (95% confidence interval 0.553–0.757; p = 0.004) at baseline and 0.737 (95% confidence interval 0.643–0.827; p < 0.001) at 1 year after initiation of treatment. Change in ISWT distance also predicted survival (p = 0.04). Heart rate (HR) and systolic blood pressure (SBP) parameters reflecting autonomic response to exercise (highest HR, change in HR, HR recovery at 1 minute >18 beats/min, highest SBP, change in SBP, and 3-minute SBP ratio) were significant predictors of survival (all p < 0.05).

In patients with PAH, the ISWT is simple to perform, allows assessment of maximal exercise capacity, is sensitive to treatment effect, predicts outcome, and has no ceiling effect. Also, measures of autonomic function made post-exercise predict survival in PAH.

The goal of the 6-min walk test (6MWT) is to enable patients to walk “as far as possible” as a measure of their functional ability. The impact of the specific walk instructions on patient 6MWT performance is unknown.

Patients with pulmonary arterial hypertension (PAH), idiopathic pulmonary fibrosis (IPF), and other forms of interstitial lung disease (ILD) were recruited to perform four identical 6MWTs with one differing instructional phrase. The standard instruction to walk “as far as possible” was substituted in random order with “as fast as possible,” “at your normal pace,” or “at a leisurely pace.”

Twenty-four patients (10 with PAH, eight with IPF, six with other ILD) were enrolled and completed all four 6MWTs. Patients attained the greatest distance with the fast instruction, exceeding the standard instruction distance by a mean of 52.7 m (P < .001). The mean difference between the fast and standard walks was 41.5 m in the PAH group, 66.5 m in the IPF group, and 53 m in the other ILD group.

Patients do not walk as far as they are able with the standard American Thoracic Society instruction for 6MWT. Changing the wording from “far” to “fast” may facilitate a better effort and greater distance during the test. It is possible that this modified 6MWT instruction may result in improved accuracy and reproducibility, thereby enhancing its clinical and research trial usefulness.

ClinicalTrials.gov; No.: NCT01789996; URL: www.clinicaltrials.gov

Because of the challenges associated with conducting large survival studies of patients with pulmonary arterial hypertension (PAH), we analyzed the surrogate markers predictive of long-term survival in a large cohort of patients treated with subcutaneous treprostinil.

A retrospective review was conducted using data from a total of 811 patients with New York Heart Association Functional Class (NYHA FC) II to IV PAH, who were treated with subcutaneous treprostinil. Patient baseline disease and on-treatment parameters were analyzed by uni- and multivariate analyses for predictive value of 3-year survival with PAH.

Among the baseline disease-related factors analyzed, there was a significantly higher risk of death (p < 0.001) associated with connective tissue disease–associated PAH relative to idiopathic PAH (hazard ratio for death [HR] 1.93), NYHA FC IV vs III (HR 2.31), pulmonary vascular resistance index (PVRI) >30 vs ≤16 mm Hg/liter/min/m² (HR 2.44) and mixed venous oxygen saturation (SVO₂) ≤55% vs >55%. The 6-minute walk distance (6MWD) of ≤295 m after 12 weeks of treprostinil treatment was associated with reduced survival at 3 years (58%). A ≥20-m increase from baseline in 6MWD was associated with greater survival (80%) vs smaller walk increments (69%; p = 0.039). Treprostinil dose of ≥40 ng/kg/min (p < 0.001) and every 10-ng/kg/min dose increase (p = 0.009) resulted in improved long-term survival. In a multivariate analysis, only SVO₂, 6MWD and treprostinil dose were significant on-treatment predictors (p < 0.02) of survival.

Disease etiology, baseline factors (NYHA FC, PVRI and SVO₂) and on-treatment factors (6MWD, SVO₂ and treprostinil dose) were predictors of survival in this study and may be used to aid in treatment optimization.

Recent discoveries in the disease pathophysiology of pulmonary arterial hypertension have been translated into effective therapies tested in clinical trials. The studies have focused on surrogate and intermediate end points, thought to reflect quantity and quality of life, respectively. The authors present the necessary requirements for establishing the reliability and validity of such end points before they may be used dependably. The authors also review the available data, strengths, and weaknesses of potential end points in pulmonary arterial hypertension.

Progress in understanding the basic biology and the development of new therapies for pulmonary arterial hypertension have led to improvements in survival. This article reviews clinically important changes in the classification of the pulmonary hypertensive diseases, as well as the epidemiology of various forms of pulmonary hypertension. The risk factors for the development of pulmonary arterial hypertension, prognostic markers, and the effects of current therapies on survival are discussed.