What is Myocardial Bridge
A myocardial bridge is a congenital coronary anomaly where muscle fiber bundles overlie a segment of an epicardial coronary artery, causing the artery to tunnel through the myocardium instead of following its normal epicardial course. 1
Anatomical Definition and Prevalence
The muscle overlying the artery is termed the "myocardial bridge," while the segment running through the myocardium is called the "tunneled artery." 2
The reported incidence varies dramatically depending on detection method: 0.5-4.5% on coronary angiography versus 15-85% in pathological (autopsy) studies, indicating most bridges are clinically silent and undetected during life. 1
The left anterior descending artery (LAD) is affected in almost all cases, though bridges can occur in any epicardial coronary artery. 1, 3
Pathophysiology and Clinical Significance
The bridge causes systolic compression of the coronary artery during the cardiac cycle, which is the characteristic angiographic finding. 1
In symptomatic patients, quantitative coronary angiography demonstrates delayed and incomplete vessel diameter gain during mid to late diastole, not just systolic narrowing. 1
Pathological studies indicate that vessels with tunneled length >3 mm deep beneath the epicardium create the greatest vulnerability for cardiac events. 1
Potential Complications
While most myocardial bridges are benign, they can cause serious complications in select cases:
- Myocardial ischemia and angina due to reduced coronary blood flow reserve 4, 3
- Myocardial infarction 1, 5
- Malignant ventricular arrhythmias and ventricular tachycardia 1, 5
- Atrioventricular block 1
- Sudden cardiac death (rare but documented) 1
Association with Other Conditions
Myocardial bridges occur in 30-50% of patients with hypertrophic cardiomyopathy and have been suggested as a possible cause of sudden cardiac death in this population. 1, 3
Bridges may facilitate atherosclerosis development in the proximal segment (upstream from the bridge) due to abnormal hemodynamics and endothelial injury from retrograde blood flow during systole. 5, 6
Clinical Presentation
Most myocardial bridges are asymptomatic and discovered incidentally. 1, 7
When symptomatic, patients typically present with:
- Stable angina pectoris (more common in isolated bridges without atherosclerosis) 5
- Exercise-induced chest pain that resembles typical angina 1
- Acute coronary syndrome (more common when atherosclerosis is superimposed on the bridge) 5
The risk of acute coronary syndrome rises significantly when atherosclerosis develops proximal to the myocardial bridge. 5
Diagnostic Evaluation
Coronary angiography visualizes the characteristic systolic compression of the artery, appearing as a "milking effect" during the cardiac cycle. 1, 4
For functional assessment of hemodynamic significance:
- ECG exercise testing, dobutamine stress echocardiography, or myocardial perfusion scintigraphy are recommended to evaluate for inducible ischemia. 1, 4, 3
- Intracoronary Doppler flow velocity measurement can provide functional insight in selected cases. 1
Prognosis
The long-term prognosis of isolated myocardial bridges appears to be excellent in most cases, though rare complications can occur. 1, 3
Consider myocardial bridging in young patients presenting with angina or its equivalents, particularly if they lack multiple traditional risk factors for coronary artery disease. 5