Prevalence of myocardial bridging associated with coronary endothelial dysfunction in patients with chest pain and non-obstructive coronary artery disease

Aims: Myocardial bridging (MB), characterised by the epicardial coronary vessel diving into the myocardium, is present in up to one third of adults and is associated with angina and acute coronary syndromes. MB is accompanied by altered blood flow mechanics and regional changes in wall sheer stress. The purpose of this study was to determine the association between myocardial bridging and coronary endothelial dysfunction. Methods and results: Patients presenting with chest pain and found to have non-obstructive CAD (stenosis <40%) on angiography underwent an invasive assessment of epicardial and microvascular endothelial function. Epicardial endothelial function was assessed by measuring the percent change in coronary artery diameter in response to intracoronary infusions of acetylcholine (%Delta CADAch). Epicardial endothelial dysfunction was defined as a %Delta CADAch of <-20%. Microvascular endothelial function was assessed by the percent change in coronary blood flow in response to intracoronary infusions of acetylcholine (%Delta CBFAch), and microvascular endothelial dysfunction was defined as a %Delta CBFAch of <50%. MB was diagnosed angiographically by identifying the characteristic reduction in minimal luminal diameter during systole. Patients were divided into those with and those without MB, and the frequency of epicardial endothelial dysfunction and microvascular endothelial dysfunction was compared between patients with versus those without MB. Between 1993 and 2012, 1,469 patients (mean age 50.4 years, 35% male) underwent coronary angiography and invasive testing of endothelial function. Two hundred and eight (14.2%) patients were found to have MB in the LAD. Patients with any MB had a significantly higher frequency of endothelial dysfunction within the mid and/or distal vessel segment compared to patients without MB (60.1% vs 50.4%, p=0.012). In multivariate analyses, mid and/or distal vessel MB was a significant predictor of mid and/or distal vessel epicardial endothelial dysfunction (OR 1.44, 95% CI: 1.04-2.00, p=0.029) and of microvascular endothelial dysfunction (OR 1.34, 95% CI: 1.00-1.82, p=0.050). Conclusions: MB co-localises with epicardial endothelial dysfunction and is significantly associated with microvascular endothelial dysfunction in symptomatic patients with non-obstructive CAD, supporting its potential role as a mechanism for angina in symptomatic patients with MB.