Using a knowledge translation program to facilitate guideline- and evidence-based patient management: the PAH-QuERI Extension Program.

The Pulmonary Arterial Hypertension-Quality Enhancement Research Initiative Extension Program was designed to support physicians' adherence to pulmonary arterial hypertension (PAH) guidelines. Guidelines were followed in >95% of patients with functional class (FC) II/III, but for only 28.6% of FC IV patients (Month 36). Low adherence was driven by FC IV patients' preference to avoid parenteral treatment.

The physiological basis of pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is a rare dyspnoea-fatigue syndrome caused by a progressive increase in pulmonary vascular resistance and eventual right ventricular (RV) failure. In spite of extensive pulmonary vascular remodelling, lung function in PAH is generally well preserved, with hyperventilation and increased physiological dead space, but minimal changes in lung mechanics and only mild to moderate hypoxaemia and hypocapnia. Hypoxaemia is mainly caused by a low mixed venous oxygen tension from a decreased cardiac output. Hypocapnia is mainly caused by an increased chemosensitivity. Exercise limitation in PAH is cardiovascular rather than ventilatory or muscular. The extent of pulmonary vascular disease in PAH is defined by multipoint pulmonary vascular pressure-flow relationships with a correction for haematocrit. Pulsatile pulmonary vascular pressure-flow relationships in PAH allow for the assessment of RV hydraulic load. This analysis is possible either in the frequency domain or in the time domain. The RV in PAH adapts to increased afterload by an increased contractility to preserve its coupling to the pulmonary circulation. When this homeometric mechanism is exhausted, the RV dilates to preserve flow output by an additional heterometric mechanism. Right heart failure is then diagnosed by imaging of increased right heart dimensions and clinical systemic congestion signs and symptoms. The coupling of the RV to the pulmonary circulation is assessed by the ratio of end-systolic to arterial elastances, but these measurements are difficult. Simplified estimates of RV-pulmonary artery coupling can be obtained by magnetic resonance or echocardiographic imaging of ejection fraction.

Long-Term Survival, Safety and Tolerability with Selexipag in Patients with Pulmonary Arterial Hypertension: Results from GRIPHON and its Open-Label Extension.

INTRODUCTION: In the event-driven GRIPHON randomised-controlled trial, the oral prostacyclin receptor agonist selexipag significantly reduced the risk of disease progression (composite primary endpoint of morbidity/mortality), compared with placebo, in patients with pulmonary arterial hypertension (PAH). The ongoing open-label extension study (GRIPHON OL) collects further data on long-term safety, tolerability, and survival of PAH patients treated with selexipag. METHODS: Patients randomised to selexipag or placebo in GRIPHON could enter GRIPHON OL either after experiencing a morbidity event during double-blind treatment or at the end of the study. Patients were followed for adverse events (AE) and survival from selexipag initiation up to 3 days and 30 days after end of treatment, respectively. Data are presented up to a cut-off date of 1 September 2019. RESULTS: Overall, 953 patients in GRIPHON and GRIPHON OL were treated with selexipag. At the time of selexipag initiation, 81.2% of patients were receiving background PAH therapy. Median (min, max) exposure to selexipag was 31.7 months (0, 106), corresponding to a total of 3054.4 patient-years. The most frequently reported AEs were related to known prostacyclin-related effects or underlying disease. There were 305 (32.0%) patients who experienced an AE leading to treatment discontinuation. Survival during GRIPHON and GRIPHON OL was assessed for the 574 patients randomised to selexipag in GRIPHON. Kaplan-Meier survival estimates (95%CI) at 1, 3, 5 and 7 years were 92.0% (89.4, 94.0), 79.3% (75.4, 82.6), 71.2% (66.5, 75.3) and 63.0% (57.4, 68.1), respectively. CONCLUSIONS: These results provide the longest follow-up period published to date for a PAH therapy. The safety profile of selexipag over this extended treatment period was consistent with that observed in GRIPHON. A large proportion of the population was receiving background therapy at selexipag initiation, providing further insight into the long-term safety of selexipag as part of a combination therapy regimen. TRIAL REGISTRATION: ClinicalTrials.gov Identifiers: NCT01106014 and NCT01112306.

The impact of comorbidities on selexipag treatment effect in patients with pulmonary arterial hypertension: insights from the GRIPHON study.

AIMS: The number of pulmonary arterial hypertension (PAH) patients with comorbidities is increasing and there are limited data on response to PAH-targeted therapies in this population. These post hoc analyses explored the effect of selexipag in PAH patients with cardiovascular comorbidities in the GRIPHON study. METHODS AND RESULTS: Randomized patients (n = 1156) were classified using three methods: (i) by subgroups defined according to previously published comorbidity count and restrictive haemodynamic criteria: Subgroup A (<3 comorbidities and haemodynamic criteria met; n = 962) and Subgroup B (≥3 comorbidities and/or haemodynamic criteria not met; n = 144); comorbidities included body mass index ≥30 kg/m2 , essential hypertension, diabetes, history of coronary artery disease; (ii) by number of comorbidities, with addition of atrial fibrillation (0, 1, 2, 3, 4, or 5); (iii) by presence of individual comorbidities. Selexipag to placebo hazard ratios (HR) and 95% confidence intervals (CI) for morbidity/mortality (primary composite endpoint) were estimated using Cox regression adjusting selexipag effect for baseline covariates. Approximately half of the patients in GRIPHON (n = 584; 50.5%) had comorbidities. Selexipag reduced the risk of a morbidity/mortality event compared with placebo in both Subgroup A (HR 0.66, 95% CI 0.53, 0.82) and Subgroup B (HR 0.50, 95% CI 0.26, 0.96), with no evidence of an inconsistent treatment effect between subgroups (interaction p = 0.432). Consistent results were observed in analyses by number and by specific type of comorbidity. CONCLUSION: Selexipag reduces the risk of a morbidity/mortality event vs. placebo irrespective of patient comorbidity status, suggesting that comorbidity status does not influence the treatment effect of selexipag.

Relationship Between Time From Diagnosis and Morbidity/Mortality in Pulmonary Arterial Hypertension: Results From the Phase III GRIPHON Study.

BACKGROUND: Early initiation of pulmonary arterial hypertension (PAH) therapies is associated with improved long-term outcomes, yet data on the early use of prostacyclin pathway agents are limited. In these post hoc analyses of the Prostacyclin (PGI2) Receptor Agonist In Pulmonary Arterial Hypertension (GRIPHON) study, the largest randomized controlled trial for PAH to date, the prognostic value of time from diagnosis and its impact on treatment response were examined. RESEARCH QUESTION: How does time from diagnosis impact morbidity/mortality events and response to selexipag treatment in patients with PAH? STUDY DESIGN AND METHODS: The GRIPHON study randomly assigned 1,156 patients with PAH to selexipag or placebo treatment. Patients were categorized post hoc into a time from diagnosis of ≤ 6 months and > 6 months at randomization. Hazard ratios (selexipag vs placebo) were calculated for the primary end point of morbidity/mortality by time from diagnosis using Cox proportional hazard models. RESULTS: Time from diagnosis was ≤ 6 months in 34.9% and > 6 months in 65.1% of patients. Time from diagnosis was prognostic of morbidity/mortality, with newly diagnosed patients having a poorer long-term outcome than patients diagnosed for longer. Compared with placebo, selexipag reduced the risk of morbidity/mortality in patients with a time from diagnosis of ≤ 6 months and > 6 months, with a more pronounced effect in newly diagnosed patients (hazard ratio, 0.45 [95% CI, 0.33-0.63] and 0.74 [95% CI, 0.57-0.96], respectively; P = .0219 for interaction). INTERPRETATION: In the GRIPHON study, newly diagnosed PAH patients had a worse prognosis than patients with a longer time from diagnosis. The benefit of selexipag treatment on disease progression was more pronounced in patients treated earlier than in patients treated later. TRIAL REGISTRY: ClinicalTrials.gov; No.: NCT01106014; URL: www.clinicaltrials.gov.

Comparative bioavailability of inhaled treprostinil administered as LIQ861 and Tyvaso® in healthy subjects.

INTRODUCTION: Treprostinil is a synthetic prostacyclin analogue approved for inhalation administration to patients with pulmonary arterial hypertension (PAH) via nebulized Tyvaso® inhalation solution. LIQ861 is an inhaled, dry-powder formulation of treprostinil produced using Print® (Particle Replication in Nonwetting Templates) technology, a proprietary process for designing and producing highly uniform drug particles. METHODS: We conducted comparative bioavailability analyses of treprostinil exposure from LIQ861 (79.5 µg capsule [approximate delivered dose of 58.1 µg treprostinil]) compared with Tyvaso® (9 breaths [approximate delivered dose of 54 µg treprostinil]). RESULTS: Treprostinil exposure parameters had least squares geometric mean ratios (LIQ861: Tyvaso®) between 0.9 and 1.0 with 90% confidence intervals contained within 0.8 to 1.25. LIQ861 and Tyvaso® were both well tolerated. DISCUSSION: Results showed comparable bioavailability of treprostinil and similar tolerability for LIQ861 and Tyvaso® administered to healthy adults. CONCLUSIONS: Given the comparable treprostinil bioavailability and similar safety profiles of LIQ861 and Tyvaso®, LIQ861 fulfills a significant unmet need for PAH patients by maximizing the therapeutic benefits of treprostinil by safely delivering doses to the lungs in 1 to 2 breaths using a discreet, convenient, easy-to-use inhaler.

Intravascular Ultrasound Pulmonary Artery Denervation to Treat Pulmonary Arterial Hypertension (TROPHY1): Multicenter, Early Feasibility Study.

OBJECTIVES: The aim of this study was to investigate whether therapeutic intravascular ultrasound pulmonary artery denervation (PDN) is safe and reduces pulmonary vascular resistance (PVR) in patients with pulmonary arterial hypertension (PAH) on a minimum of dual oral therapy. BACKGROUND: Early studies have suggested that PDN can reduce PVR in patients with PAH. METHODS: TROPHY1 (Treatment of Pulmonary Hypertension 1) was a multicenter, international, open-label trial undertaken at 8 specialist centers. Patients 18 to 75 years of age with PAH were eligible if taking dual oral or triple nonparenteral therapy and not responsive to acute vasodilator testing. Eligible patients underwent PDN (TIVUS System). The primary safety endpoint was procedure-related adverse events at 30 days. Secondary endpoints included procedure-related adverse events, disease worsening and death to 12 months, and efficacy endpoints that included change in pulmonary hemodynamic status, 6-min walk distance, and quality of life from baseline to 4 or 6 months. Patients were to remain on disease-specific medication for the duration of the study. RESULTS: Twenty-three patients underwent PDN, with no procedure-related serious adverse events reported. The reduction in PVR at 4- or 6-month follow-up was 94 ± 151 dyn·s·cm-5 (p = 0.001) or 17.8%, which was associated with a 42 ± 63 m (p = 0.02) increase in 6-min walk distance and a 671 ± 1,555 step (p = 0.04) increase in daily activity. CONCLUSIONS: In this multicenter early feasibility study, PDN with an intravascular ultrasound catheter was performed without procedure-related adverse events and was associated with a reduction in PVR and increases in 6-min walk distance and daily activity in patients with PAH on background dual or triple therapy.

Risk assessment in pulmonary arterial hypertension: Insights from the GRIPHON study.

BACKGROUND: Approaches to risk assessment in pulmonary arterial hypertension (PAH) include the noninvasive French risk assessment approach (number of low-risk criteria based on the European Society of Cardiology and European Respiratory Society guidelines) and Registry to Evaluate Early and Long-term PAH Disease Management (REVEAL) 2.0 risk calculator. The prognostic and predictive value of these methods for morbidity/mortality was evaluated in the predominantly prevalent population of GRIPHON, the largest randomized controlled trial in PAH. METHODS: GRIPHON randomized 1,156 patients with PAH to selexipag or placebo. Post-hoc analyses were performed on the primary composite end-point of morbidity/mortality by the number of low-risk criteria (World Health Organization functional class I-II; 6-minute walk distance >440 m; N-terminal pro-brain natriuretic peptide <300 ng/liter) and REVEAL 2.0 risk category. Hazard ratios and 95% confidence intervals were calculated using Cox proportional hazard models. RESULTS: Both the number of low-risk criteria and the REVEAL 2.0 risk category were prognostic for morbidity/mortality at baseline and any time-point during the study. Patients with 3 low-risk criteria at baseline had a 94% reduced risk of morbidity/mortality compared to patients with 0 low-risk criteria and were all categorized as low-risk by REVEAL 2.0. The treatment effect of selexipag on morbidity/mortality was consistent irrespective of the number of low-risk criteria or the REVEAL 2.0 risk category at any time-point during the study. Selexipag-treated patients were more likely to increase their number of low-risk criteria from baseline to week 26 than placebo-treated patients (odds ratio 1.69, p = 0.0002); similar results were observed for REVEAL 2.0 risk score. CONCLUSIONS: These results support the association between risk profile and long-term outcome and suggest that selexipag treatment may improve risk profile.

Patients with pulmonary arterial hypertension with and without cardiovascular risk factors: Results from the AMBITION trial.

BACKGROUND: The purpose of this study was to compare patients with pulmonary arterial hypertension enrolled in the AMBITION trial with (excluded from the primary analysis set [ex-primary analysis set]) and without (primary analysis set) multiple risk factors for left ventricular diastolic dysfunction. METHODS: Treatment-naive patients with pulmonary arterial hypertension were randomized to once-daily ambrisentan and tadalafil combination therapy, ambrisentan monotherapy, or tadalafil monotherapy. The primary end point was time from randomization to first adjudicated clinical failure event. RESULTS: Primary analysis set patients (n = 500), compared with ex-primary analysis set patients (n = 105), were younger (mean, 54.4 vs 62.1 years) with greater baseline 6-minute walk distance (median, 363.7 vs 330.5 meters) and fewer comorbidities (e.g., hypertension and diabetes). Treatment effects of initial combination therapy vs pooled monotherapy were directionally the same for both populations, albeit of a lower magnitude for ex-primary analysis set patients. Initial combination therapy reduced the risk of clinical failure compared with pooled monotherapy in primary analysis set patients (hazard ratio, 0.50; 95% confidence interval, 0.35-0.72), whereas the effect was less clear in ex-primary analysis set patients (hazard ratio, 0.70; 95% confidence interval, 0.35-1.37). Overall, primary analysis set patients had fewer clinical failure events (25% vs 33%), higher rates of satisfactory clinical response (34% vs 24%), and lower rates of permanent study drug withdrawal due to adverse events (16% vs 31%) than ex-primary analysis set patients. CONCLUSIONS: Efficacy of initial combination therapy vs pooled monotherapy was directionally similar for primary analysis set and ex-primary analysis set patients. However, ex-primary analysis set patients (with multiple risk factors for left ventricular diastolic dysfunction) experienced higher rates of clinical failure events and the response to combination therapy vs monotherapy was attenuated. Tolerability was better in primary analysis set than ex-primary analysis set patients.

Integrating Data From Randomized Controlled Trials and Observational Studies to Assess Survival in Rare Diseases.

Background Conducting randomized controlled trials to investigate survival in a rare disease like pulmonary arterial hypertension has considerable ethical and logistical constraints. In many studies, such as the Study with an Endothelin Receptor Antagonist in Pulmonary Arterial Hypertension to Improve Clinical Outcome (SERAPHIN) randomized controlled trial, evaluating survival is further complicated by bias introduced by allowing active therapy among placebo-treated patients who clinically deteriorate. Methods and Results SERAPHIN enrolled and followed patients in the same time frame as the US Registry to Evaluate Early And Long-term PAH Disease Management, providing an opportunity to compare observed survival for SERAPHIN patients with predicted survival had they received real-world treatment as in the Registry to Evaluate Early And Long-term PAH Disease Management. From the Registry to Evaluate Early And Long-term PAH Disease Management (N=3515), 734 patients who met SERAPHIN eligibility criteria were selected and their data used to build a prediction model for time to death up to 3 years based on 10 baseline prognostic variables. The model was used to predict a survival curve for each of the 742 SERAPHIN patients via their baseline variables. The average of these predicted survival curves was compared with observed survival of the placebo (n=250) and macitentan 10 mg (n=242) groups using a log-rank test and Cox proportional hazard model. Observed mortality risk for patients randomized to placebo, 62% of whom were taking background pulmonary arterial hypertension therapy, tended to be lower than that predicted for all SERAPHIN patients (16% lower; P=0.259). The observed placebo survival curve closely approximated the predicted survival curve for the first 15 months. Beyond that time, observed risk of mortality decreased compared with predicted mortality, potentially reflecting the impact of crossover of patients in the placebo group to active therapy. Over 3 years, risk of mortality observed with macitentan 10 mg was 35% lower than predicted mortality ( P=0.010). Conclusions These analyses show that, in a rare disease, real-world observational data can complement randomized controlled trial data to overcome some challenges associated with assessing survival in the setting of a randomized controlled trial. Clinical Trial Registration https://www.clinicaltrials.gov . Unique identifiers: NCT00660179 and NCT00370214.

Association of N-Terminal Pro Brain Natriuretic Peptide and Long-Term Outcome in Patients With Pulmonary Arterial Hypertension.

BACKGROUND: NT-proBNP (N-terminal pro brain natriuretic peptide) levels are included in the multiparametric risk assessment approach for pulmonary arterial hypertension (PAH) outlined in PAH guidelines. However, data supporting the use of NT-proBNP risk thresholds in assessing prognosis in PAH are limited. The GRIPHON trial (Prostacyclin [PGI2] Receptor Agonist In Pulmonary Arterial Hypertension) provides an opportunity to assess the prognostic value of NT-proBNP thresholds in a controlled clinical trial and to evaluate the response to selexipag according to these thresholds. METHODS: The event-driven GRIPHON trial randomly assigned patients to selexipag or placebo. NT-proBNP was measured at regular intervals in GRIPHON. Here, patients were categorized post hoc into low, medium, and high NT-proBNP subgroups according to 2 independent sets of thresholds: (1) baseline tertiles: <271 ng/L; 271 to 1165 ng/L; >1165 ng/L; and (2) 2015 European Society of Cardiology/European Respiratory Society guidelines cutoffs: <300 ng/L; 300 to 1400 ng/L; >1400 ng/L. Hazard ratios (selexipag versus placebo) with 95% CIs were calculated for the primary end point (composite morbidity/mortality events) by NT-proBNP category at baseline using Cox proportional-hazards models, and at any time during the exposure period using a time-dependent Cox model. RESULTS: With both thresholds, baseline and follow-up NT-proBNP categories were highly prognostic for future morbidity/mortality events during the study ( P<0.0001). In the time-dependent analysis, the risk of experiencing a morbidity/mortality event was 92% and 83% lower in selexipag-treated patients with a low and medium NT-proBNP level, and 90% and 56% lower in placebo-treated patients with a low and medium NT-proBNP level, in comparison with patients with a high NT-proBNP level. Selexipag reduced the risk of morbidity/mortality events across all 3 NT-proBNP categories in both the baseline and time-dependent analyses, with a more pronounced treatment benefit of selexipag seen in the medium and low NT-proBNP subgroups (interaction P values 0.20 and 0.007 in the baseline and time-dependent analyses). CONCLUSIONS: These analyses further establish the prognostic relevance of NT-proBNP levels in PAH and provide first evidence for the association of NT-proBNP level and treatment response. Using 2 similar sets of thresholds, these analyses support the relevance of the low, medium, and high NT-proBNP categories as part of the multiparametric risk assessment approach outlined in the European Society of Cardiology/European Respiratory Society guidelines for the management of PAH patients. CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov . Unique identifier: NCT01106014.

Selexipag treatment for pulmonary arterial hypertension associated with congenital heart disease after defect correction: insights from the randomised controlled GRIPHON study.

AIMS: Patients with pulmonary arterial hypertension associated with congenital heart disease (CHD-PAH) after defect correction have a poor prognosis compared with other CHD-PAH patients. Therefore, it is important that these patients are treated as early and effectively as possible. Evidence supporting the use of PAH therapies in patients with corrected CHD-PAH from randomised controlled trials is limited. The purpose of these analyses was to characterise the corrected CHD-PAH patients from the GRIPHON study and examine the response to selexipag. METHODS AND RESULTS: Out of the 110 patients diagnosed with corrected CHD-PAH, 55 had atrial septal defects, 38 had ventricular septal defects, 14 had persistent ducti arteriosus, and 3 had defects not further specified. Hazard ratios (HR) and 95% confidence intervals (CI) for the primary composite endpoint were calculated using Cox proportional hazard models. Compared with the non-CHD patients from GRIPHON, patients with corrected CHD-PAH were slightly younger, with a greater proportion being treatment-naive and in World Health Organization functional class I/II. The rate of the primary composite endpoint of morbidity/mortality was lower in patients with corrected CHD-PAH who were treated with selexipag compared with those treated with placebo (HR 0.58; 95% CI 0.25, 1.37). The most common adverse events were those known to be related to selexipag. CONCLUSIONS: These post-hoc analyses of GRIPHON provide valuable information about a large population of patients with corrected CHD-PAH, and suggest that selexipag may delay disease progression and was well-tolerated in patients with corrected CHD-PAH.

Clinical trial design and new therapies for pulmonary arterial hypertension.

Until 20 years ago the treatment of pulmonary arterial hypertension (PAH) was based on case reports and small series, and was largely ineffectual. As a deeper understanding of the pathogenesis and pathophysiology of PAH evolved over the subsequent two decades, coupled with epidemiological studies defining the clinical and demographic characteristics of the condition, a renewed interest in treatment development emerged through collaborations between international experts, industry and regulatory agencies. These efforts led to the performance of robust, high-quality clinical trials of novel therapies that targeted putative pathogenic pathways, leading to the approval of more than 10 novel therapies that have beneficially impacted both the quality and duration of life. However, our understanding of PAH remains incomplete and there is no cure. Accordingly, efforts are now focused on identifying novel pathogenic pathways that may be targeted, and applying more rigorous clinical trial designs to better define the efficacy of these new potential treatments and their role in the management scheme. This article, prepared by a Task Force comprised of expert clinicians, trialists and regulators, summarises the current state of the art, and provides insight into the opportunities and challenges for identifying and assessing the efficacy and safety of new treatments for this challenging condition.

Initial combination therapy with ambrisentan + tadalafil on pulmonary arterial hypertension‒related hospitalization in the AMBITION trial.

BACKGROUND: In the randomized, double-blind, event-driven AMBITION study, initial combination therapy with ambrisentan and tadalafil was associated with a 50% reduction in risk of clinical failure (first occurrence of all-cause death, hospitalization for worsening pulmonary arterial hypertension [PAH], disease progression, or unsatisfactory long-term clinical response) vs pooled monotherapy. These results were primarily driven by a reduction in PAH-related hospitalization in the combination therapy group, although a significant effect was not observed in a post-hoc analysis of all-cause hospitalization. METHODS: The effect of initial combination therapy with ambrisentan and tadalafil in AMBITION was further explored to study PAH-related hospitalization, which was not reported in the primary publication. RESULTS: Initial combination therapy was associated with a 63% reduction in risk of PAH-related hospitalization when compared with pooled monotherapy (hazard ratio [HR] 0.372, 95% confidence interval [CI] 0.217 to 0.639, p = 0.0002). For every 9 patients treated with combination therapy vs monotherapy, 1 PAH-related hospitalization could be prevented over a 1-year period. Serious adverse events leading to hospitalization, not necessarily PAH-related, occurred in 87 of 253 (34%) and 89 of 247 (36%) of patients on combination therapy and pooled monotherapy, respectively (post-hoc summary). CONCLUSIONS: Initial combination therapy with ambrisentan and tadalafil was found to reduce the risk of PAH-related hospitalization by 63% compared with pooled monotherapy.

Risk-stratified outcomes with initial combination therapy in pulmonary arterial hypertension: Application of the REVEAL risk score.

BACKGROUND: The multinational AMBITION study demonstrated a 50% risk reduction in time to first clinical failure event (TtCF, a composite of death, hospitalization for worsening pulmonary arterial hypertension [PAH], disease progression, or unsatisfactory long-term clinical response) in treatment-naive Functional Class II and III PAH patients initiated on combination therapy (ambrisentan and tadalafil) vs monotherapy. A post-hoc analysis of AMBITION data by risk stratification, as determined by baseline REVEAL risk score, was undertaken to better assess the impact of combination therapy. METHODS: Patients were randomized 2:1:1 to initial combination therapy with ambrisentan 10 mg plus tadalafil 40 mg vs either drug plus placebo, respectively. Baseline REVEAL risk scores in the 605 patients were grouped by low, intermediate, or high risk. Adjudicated outcomes (TtCF and post-hoc composite end-point of time to first PAH hospitalization or death) were assessed by risk group and treatment assignment. RESULTS: At baseline, risk groups were similarly represented across treatment assignments as low (16%), intermediate (46%), and high (38%) risk. Greater risk was associated with worse outcome. At each level of risk, patients on combination therapy had significantly fewer TtCF or PAH hospitalization/death events relative to those on monotherapy, and discontinuations due to adverse events were not higher on combination therapy. CONCLUSIONS: This post-hoc analysis comparing outcomes by REVEAL risk group has shown that, at all levels of risk, patients enrolled in AMBITION receiving initial combination therapy have superior outcomes and, even in those assessed as low risk, initial combination therapy was clinically beneficial.