The impact of myocardial bridge on coronary artery spasm and long-term clinical outcomes in patients without significant atherosclerotic stenosis

Background and aims: Myocardial bridge (MB) and coronary artery spasm (CAS) can induce a sustained chest pain, acute coronary syndrome (ACS) and even sudden cardiac death. The aim of this study is to evaluate the relationship between MB and CAS and its impact on long-term clinical outcomes. Methods: A total of 812 patients with MB without significant coronary artery disease (CAD), who underwent acetylcholine (ACH) provocation test, were enrolled. Significant CAS was defined as ≥70% temporary narrowing by ACH test, and MB was defined as the characteristic phasic systolic compression of the coronary artery with a decrease of more than 30% in diameter on the angiogram after intracoronary nitroglycerin infusion. To adjust baseline confounders, logistic regression analysis was performed. The primary endpoint was incidence of CAS, and secondary endpoints were major adverse cardiac events (MACE) and recurrent angina requiring repeat coronary angiography (CAG) at 5 years. Results: MB is closely implicated in a high incidence of CAS, spontaneous spasm, ischemic ECG change and chest pain during ACH provocation test. In addition, MB of various severity and reference vessel size was substantially implicated in CAS incidence, and severe MB was a strong risk factor of CAS. MB patients with CAS were shown to have a higher rate of recurrent angina compared with MB patients without CAS, up to a 5-year follow-up. However, there were no differences regarding the incidence of MACE. Conclusions: Severe MB was associated with high incidence of CAS, and MB patients with CAS were likely to have a higher incidence of recurrent angina. Intensive medical therapy and close clinical follow-up are needed for better clinical outcomes in MB patients with CAS.