What is Myocardial Bridge?
A myocardial bridge is a congenital coronary anomaly in which a segment of an epicardial coronary artery takes an intramyocardial course, becoming covered by overlying myocardium that causes systolic compression of the vessel. 1, 2
Anatomic Characteristics
The left anterior descending artery is affected in almost all cases, making it the predominant location for this anatomic variant. 2
The overlying muscle is termed the "myocardial bridge," while the intramyocardial segment is called the "tunneled artery." 3
Pathological studies indicate that vessels with tunneled length deeper than 3 mm beneath the epicardium and longer than 3 mm create the greatest vulnerability for cardiac events. 1, 4
Epidemiology and Detection
The reported incidence varies dramatically by detection method: 0.5-4.5% on coronary angiography versus 15-85% at autopsy, indicating that most bridges are clinically silent and only detected incidentally. 2
Myocardial bridging occurs in 30-50% of patients with hypertrophic cardiomyopathy and has been implicated as a possible cause of sudden cardiac death in this population. 1, 2, 5
Pathophysiology and Clinical Significance
The characteristic angiographic finding is systolic compression of the artery during the cardiac cycle, which distinguishes it from atherosclerotic disease that typically causes fixed stenosis. 2
Vessel narrowing occurs due to transient myocardial compression during systole, with quantitative coronary angiography demonstrating delayed and incomplete vessel diameter recovery during mid-to-late diastole in symptomatic patients. 2
Although most myocardial bridges are benign, they can cause myocardial ischemia, myocardial infarction, malignant ventricular arrhythmias, atrioventricular block, and sudden cardiac death in select cases. 2, 6
The mechanism of ischemia involves impaired coronary blood flow from systolic compression that can persist into diastole, potentially causing supply-demand mismatch. 1
Coronary vasospasm related to bridge-induced endothelial dysfunction can explain severe presentations including ventricular fibrillation caused by ischemia. 6
Clinical Presentations
Most patients with myocardial bridging are asymptomatic because coronary perfusion occurs primarily during diastole. 7
When symptomatic, patients often present with exertional angina, though some develop more severe conditions such as unstable angina or myocardial infarction. 6
Sudden cardiac death typically occurs in males during or after physical activity, with myocardial bridging potentially leading to syncope through myocardial ischemia-induced arrhythmias, particularly during exercise. 5
Common Pitfalls
Nuclear myocardial scintigraphy is usually negative in patients with isolated myocardial bridging, which can lead to missed diagnoses if functional assessment is not comprehensive. 8
The presence of systolic compression on angiography alone is not by itself a sign of ischemia or the need for intervention—functional testing is required to determine clinical significance. 8, 7