The minimal important difference in the 6-minute walk test for patients with pulmonary arterial hypertension

From short-term benefits to long-term outcomes: the evolution of clinical trials in pulmonary arterial hypertension

Abstract Over the past 2 decades, major advances in our understanding of pulmonary arterial hypertension (PAH) have led to the development of new targeted therapeutics and management strategies that have provided benefits to patients with this devastating disease. Despite such improvements, no therapies are curative, and PAH remains a progressive disease associated with high morbidity and suboptimal survival in many patients. Clinical research in PAH is currently at a crossroads. To move forward, not only are new therapies needed, but novel approaches to clinical trial design are also required. Trials should be designed to assess the longer-term benefits of investigational therapies in what has become a chronic disease. Moreover, there is a need to consider moving away from short-term trials that use markers such as the 6-minute walk distance as a measure of exercise capacity as primary end points to longer-term, event-driven trials with composite end points made up of clinically relevant measures that better reflect the ultimate goals of reducing morbidity and mortality. A shift in trial design may also be useful in overcoming some of the muted results from recent pivotal phase III studies of combination therapy by allowing the potential of these regimens to be more comprehensively assessed.

Riociguat for the treatment of pulmonary arterial hypertension

BACKGROUND

Riociguat, a soluble guanylate cyclase stimulator, has been shown in a phase 2 trial to be beneficial in the treatment of pulmonary arterial hypertension.

METHODS

In this phase 3, double-blind study, we randomly assigned 443 patients with symptomatic pulmonary arterial hypertension to receive placebo, riociguat in individually adjusted doses of up to 2.5 mg three times daily (2.5 mg-maximum group), or riociguat in individually adjusted doses that were capped at 1.5 mg three times daily (1.5 mg-maximum group). The 1.5 mg-maximum group was included for exploratory purposes, and the data from that group were analyzed descriptively. Patients who were receiving no other treatment for pulmonary arterial hypertension and patients who were receiving endothelin-receptor antagonists or (nonintravenous) prostanoids were eligible. The primary end point was the change from baseline to the end of week 12 in the distance walked in 6 minutes. Secondary end points included the change in pulmonary vascular resistance, N-terminal pro-brain natriuretic peptide (NT-proBNP) levels, World Health Organization (WHO) functional class, time to clinical worsening, score on the Borg dyspnea scale, quality-of-life variables, and safety.

RESULTS

By week 12, the 6-minute walk distance had increased by a mean of 30 m in the 2.5 mg-maximum group and had decreased by a mean of 6 m in the placebo group (least-squares mean difference, 36 m; 95% confidence interval, 20 to 52; P<0.001). Prespecified subgroup analyses showed that riociguat improved the 6-minute walk distance both in patients who were receiving no other treatment for the disease and in those who were receiving endothelin-receptor antagonists or prostanoids. There were significant improvements in pulmonary vascular resistance (P<0.001), NT-proBNP levels (P<0.001), WHO functional class (P=0.003), time to clinical worsening (P=0.005), and Borg dyspnea score (P=0.002). The most common serious adverse event in the placebo group and the 2.5 mg-maximum group was syncope (4% and 1%, respectively).

CONCLUSIONS

Riociguat significantly improved exercise capacity and secondary efficacy end points in patients with pulmonary arterial hypertension. (Funded by Bayer HealthCare; PATENT-1 and PATENT-2 ClinicalTrials.gov numbers, NCT00810693 and NCT00863681, respectively.).

Updating clinical endpoint definitions

The 6-Minute Walk Distance (6-MWD) has been the most utilized endpoint for judging the efficacy of pulmonary arterial hypertension (PAH) therapy in clinical trials conducted over the past two decades. Despite its simplicity, widespread use in recent trials and overall prognostic value, the 6-MWD has often been criticized over the past several years and pleas from several PAH experts have emerged from the literature to find alternative endpoints that would be more reliable in reflecting the pulmonary vascular resistance as well as cardiac status in PAH and their response to therapy. A meeting of PAH experts and representatives from regulatory agencies and pharmaceutical companies was convened in early 2012 to discuss the validity of current as well as emerging valuable endpoints. The current work represents the proceedings of the conference.

Health-related quality of life in a national cohort of patients with pulmonary arterial hypertension or chronic thromboembolic pulmonary hypertension

BACKGROUND

Patients with pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH) experience impaired health-related quality of life (HRQL). The objective of this study was to evaluate HRQL in a nation-wide sample.

PATIENTS AND METHODS

This is a prospective, multicenter, non-interventional study of HRQL including 139 (89%) PAH and 17 (11%) CTEPH patients (women 70.5%; mean age, 52.2) recruited from 21 Spanish hospitals. 55% had idiopathic PAH, 34% other PAH and 11% CTEPH. HRQL was measured using the Short Form 36 Health Survey (SF-36) and EuroQoL-5D (baseline and after 6 months).

RESULTS

HRQL in the patients with PAH or CTEPH was impaired. The physical component of SF-36 and the EuroQol-5D correlated with the functional class (FC). Mean EuroQol-5D visual analogical scale (EQ-5D VAS) scores were 73.5±18.4, 62.9±20.7 and 51.3±16.0 (P<.0001) in patients with FC I, II and III, respectively. Every increase of one FC represented a loss of 4.0 on the PCS SF-36 and a loss of 9.5 on the EQ-5D VAS. Eight patients who died or received a transplant during the study period presented poorer initial HRQL compared with the rest of the population. No significant changes in HRQL were observed in survivors after 6 months of follow-up.

CONCLUSIONS

HRQL is impaired in this population, especially in PAH/CTEPH patients near death. HRQL measurements could help predict the prognosis in PAH and CTPH and provide additional information in these patients.

Imatinib mesylate as add-on therapy for pulmonary arterial hypertension: results of the randomized IMPRES study

BACKGROUND

By its inhibitory effect on platelet-derived growth factor signaling, imatinib could be efficacious in treating patients with pulmonary arterial hypertension (PAH).

METHODS AND RESULTS

Imatinib in Pulmonary Arterial Hypertension, a Randomized, Efficacy Study (IMPRES), a randomized, double-blind, placebo-controlled 24-week trial, evaluated imatinib in patients with pulmonary vascular resistance ≥ 800 dyne·s·cm(-5) symptomatic on ≥ 2 PAH therapies. The primary outcome was change in 6-minute walk distance. Secondary outcomes included changes in hemodynamics, functional class, serum levels of N-terminal brain natriuretic peptide, and time to clinical worsening. After completion of the core study, patients could enter an open-label long-term extension study. Of 202 patients enrolled, 41% patients received 3 PAH therapies, with the remainder on 2 therapies. After 24 weeks, the mean placebo-corrected treatment effect on 6-minute walk distance was 32 m (95% confidence interval, 12-52; P=0.002), an effect maintained in the extension study in patients remaining on imatinib. Pulmonary vascular resistance decreased by 379 dyne·s·cm(-5) (95% confidence interval, -502 to - 255; P<0.001, between-group difference). Functional class, time to clinical worsening, and mortality did not differ between treatments. Serious adverse events and discontinuations were more frequent with imatinib than placebo (44% versus 30% and 33% versus 18%, respectively). Subdural hematoma occurred in 8 patients (2 in the core study, 6 in the extension) receiving imatinib and anticoagulation.

CONCLUSIONS

Imatinib improved exercise capacity and hemodynamics in patients with advanced PAH, but serious adverse events and study drug discontinuations were common. Further studies are needed to investigate the long-term safety and efficacy of imatinib in patients with PAH.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00902174 (core study); NCT01392495 (extension).