What is Myocardial Bridge?
A myocardial bridge is a congenital coronary anomaly where a segment of an epicardial coronary artery runs intramurally through the myocardium rather than along the heart's surface, causing the overlying muscle to compress the vessel during systole. 1
Anatomical Definition
Myocardial bridges consist of muscle fiber bundles overlying an epicardial coronary artery for a variable distance, with the intramyocardial segment referred to as a "tunneled artery." 1
The left anterior descending artery is affected in almost all cases, making it the predominant location for this anomaly. 1, 2
Pathological studies suggest that vessels with tunneled length that is long and deeper than 3 mm beneath the epicardium create the greatest vulnerability for cardiac events. 1
Prevalence and Detection
The reported incidence varies dramatically between diagnostic modalities: 0.5-4.5% on angiography versus 15-85% in pathological studies, indicating that most myocardial bridges are not detected during life. 1, 2
The typical angiographic presentation is systolic compression of the artery during the cardiac cycle, which is the hallmark finding that distinguishes this from other coronary abnormalities. 1
Clinical Significance and Pathophysiology
Although most myocardial bridges are benign and asymptomatic, they can cause myocardial ischemia, myocardial infarction, malignant ventricular arrhythmias, atrioventricular block, and sudden cardiac death in some cases. 1
The mechanism of ischemia involves systolic compression causing vessel narrowing, with quantitative coronary angiography demonstrating delayed and incomplete vessel diameter gain during mid to late diastole. 1
Myocardial bridging occurs in 30-50% of patients with hypertrophic cardiomyopathy and has been suggested as a possible cause of sudden cardiac death in these patients. 1, 2
Associated Complications
Sudden cardiac death typically occurs in males during or after physical activity, making exercise-related symptoms particularly concerning in young patients with this anomaly. 1
The condition can lead to myocardial ischemia through direct systolic compression and by enhancing coronary atherosclerosis in the segment proximal to the bridge due to abnormal hemodynamics. 3
Diagnostic Considerations
For evaluation of hemodynamic significance, ECG exercise testing, dobutamine stress echocardiography, or myocardial perfusion scintigraphy may be useful. 1, 2
Coronary angiography visualizes the characteristic systolic compression and can assess functional significance, though intracoronary Doppler flow velocity measurement may provide additional functional insight in selected cases. 1