A Clinical Approach to Diagnosis and Treatment of Left Anterior Descending Artery Myocardial Bridge

Abstract

The muscle overlying the intramyocardial segment of an epicardial coronary artery is defined as myocardial bridge (MB). The clinical relevance of MBs is extremely heterogeneous, ranging from incidental finding in asymptomatic patients to different clinical manifestations such as stable or unstable angina, arrhythmias, Takotsubo syndrome or other major cardiovascular events. Moreover, patients can evolve from "asymptomatic carriers" to "symptomatic carriers" over time. In this setting, haemodynamic assessment is challenging and optimal therapy still a matter of debate. This review summarizes epidemiology, pathophysiology, diagnostic work-up (including both morphological and functional assessment) and treatment of patients with MB involving the left anterior descending artery, suggesting a pragmatic clinical approach. A coronary artery may dip into the myocardium for varying lengths, before reappearing on epicardial surface. The muscle overlying the intramyocardial segment of the coronary artery is termed myocardial bridge (MB), being the artery running within the myocardium referred to as tunneled artery. In 70% to 98% of cases, the MB involves the left anterior descending artery (LAD) 1. Although MBs are reported to be present in about one-fourth of adults, their true prevalence varies widely according to the diagnostic method used to detect such an anatomic variant. In fact, pathological series reported higher rates of MBs compared to coronary angiography studies, in which MBs were detected as dynamic systolic compression of a coronary segment (milking effect). This mismatch is related to several factors including thickness and length of the MB, reciprocal orientation of coronary artery and myocardial fibers, intrinsic tone of the coronary artery wall, myocardial contractility and heart rate at the time of angiography, and finally observer experience 2-4. Although the presence of this congenital variant is generally considered a benign condition, patients with MB may present with silent ischemia, stable angina, acute coronary syndromes, Takotsubo cardiomyopathy, and malignant arrhythmias possibly leading to sudden cardiac death 2,5-8. From a clinical point of view, it is important to understand why some MBs are (or become) symptomatic. In other words, when does a previously asymptomatic patient with a congenital MB become symptomatic? What additional factors unmask or aggravate a MB? Anatomical determinants that need to be taken into account are not only the depth and length of vessel encasement, but also the number of septal branches arising from or near the involved LAD segment. Moreover, pathophysiological factors that may unmask or exacerbate MBs are patient's age, heart rate, left ventricle (LV) hypertrophy, and the presence of coronary