The Anti-Anginal Efficacy of Bosentan in the Coronary Slow Flow Phenomenon

Background: The Coronary Slow Flow Phenomenon (CSFP) is a coronary microvascular disorder that presents with recurrent angina for which there is no available effective therapy. The vasoconstrictor Endothelin-1 (ET-1) has been implicated in the pathophysiology of the CSFP. This study aimed to determine whether the ET-1 antagonist (Bosentan) is effective in ameliorating angina symptoms in CSFP patients. Methods: Using a randomised, double-blind, placebo-controlled, cross-over trial methodology, the anti-anginal efficacy of Bosentan 125mg bd was assessed in 23 patients with symptomatic CSFP. Study endpoints were measured following 4 weeks of therapy with the primary endpoint being angina frequency. Secondary endpoints included (1) clinical measures of angina and health status, (2) endothelial function parameters, and (3) inflammatory and oxidative stress markers. Results: There was no statistically significant reduction in angina frequency with Bosentan therapy compared to placebo (median angina episodes/4weeks [25-75% IQ]: Bosentan 14[5,36] vs Placebo 25[9,55]) although a trend for improvement in symptoms during the Bosentan phase was observed. Furthermore, Bosentan did not impact on any of the secondary endpoints compared with placebo. Conclusion: Bosentan did not have a major impact on angina frequency in patients with the CSFP. A small anti-anginal effect cannot be excluded and requires a larger trial.