Suntharalingham 2008.

Methods	Randomised, double‐blind, placebo‐controlled trial 12 weeks duration
Participants	Inclusion criteria: Adults with distal CTEPH. (WHO Group 4) Diagnosis of PH at right‐heart catheterisation using standard diagnostic criteria. CTEPH was confirmed by ventilation perfusion scanning, CT pulmonary angiography, and either catheter‐directed pulmonary angiography or magnetic resonance pulmonary angiography. All imaging had been reviewed by a panel of specialist physicians, radiologists, and surgeons to determine the distribution of disease. People with de novo distal CTEPH and those with persistent PH 3 months post‐PEA surgery were approached. Post‐PEA patients were re‐imaged prior to enrolment both with CT pulmonary angiography and magnetic resonance pulmonary angiography to ensure no proximal disease remained. Exclusion criteria: Received any PH‐specific therapy or nitrate therapy in the 6 months prior to enrolment 6MWD < 100 metres or > 450 metres n = 19
Interventions	Sildenafil at 40 mg 3 times a day (N=9) or placebo (N=10) at 2 tablets 3 times per day in a 1:1 ratio At the end of the study, all participants were transferred to open‐label sildenafil at 40 mg 3 times a day and offered repeat assessment at 12 months
Outcomes	Primary endpoint was change in 6MWD Secondary endpoints included changes in WHO class, cardiopulmonary haemodynamics, QOL scores, and NT‐proBNP
Notes	Funding source not stated Trial conducted at the Pulmonary Vascular Diseases Unit, Papworth Hospital, Cambridgeshire, UK, enrolled between August 2004 and August 2007
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not stated
Allocation concealment (selection bias)	Low risk	Placebo‐controlled
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Placebo‐controlled
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not clearly stated if outcome assessors were blinded
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Withdrawals were accounted for: Quote: "An extensive urticarial rash developed in one subject in the sildenafil arm, who was thus withdrawn from the study"
Selective reporting (reporting bias)	Low risk	Prespecified outcomes were reported
Other bias	Low risk	Other risk of bias is unlikely