The Placebo Effect in Chronic Thromboembolic Pulmonary Hypertension Trials: A Systematic Review and Meta-Analysis.

Placebo-controlled studies are crucial in clinical trials, but the placebo effect can vary across conditions. We aimed to assess the placebo effect in chronic thromboembolic pulmonary hypertension (CTEPH) trials. We conducted a systematic review and included randomized placebo-controlled trials investigating CTEPH interventions. Primary outcomes were the pre-post changes in the 6 min walk test (6MWT) and quality of life in the placebo arms. Secondary outcomes included mean pulmonary artery pressure (mPAP), pulmonary vascular resistance (PVR), cardiac index, and NT-proBNP levels. Meta-analyses were performed using random-effects models. Seven trials with 270 CTEPH patients in placebo arms were analyzed. The average 6MWT change was not significant (-1.31 m; 95%CI -12.49 to +9.79). Quality of life with EQ-5D was not significantly improved (-0.04; 95%CI -0.10 to +0.02). mPAP, PVR, cardiac index, and NT-proBNP also demonstrated non-significant changes with small magnitudes. The placebo effect in CTEPH trials was not statistically significant and had small magnitude but should not discourage the use of placebo-controlled trials where applicable and ethical.