Myocardial Bridging: Definition and Clinical Significance
Myocardial bridging refers to muscle fiber bundles that overlay an epicardial coronary artery for a variable distance, causing the vessel to tunnel through the myocardium rather than remaining on the heart's surface. 1
Anatomic Features
The left anterior descending artery is affected in almost all cases of myocardial bridging, making it the predominant location for this anatomic variant 1
The reported incidence varies dramatically between detection methods: 0.5-4.5% on angiography versus 15-85% at autopsy, indicating that most bridges are clinically silent and only detected incidentally 1
The bridge consists of myocardial muscle fibers that create a "tunnel" through which the coronary artery passes, subjecting the vessel to external compression during cardiac contraction 1
Pathophysiology and Clinical Presentation
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 1
Vessel narrowing occurs due to transient myocardial compression during systole, and quantitative coronary angiography demonstrates delayed and incomplete vessel diameter recovery during mid-to-late diastole in symptomatic patients 1
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 1
Clinical Significance and Risk Stratification
Myocardial bridges occur in 30-50% of patients with hypertrophic cardiomyopathy and have been implicated as a possible cause of sudden cardiac death in this population 1, 2
The long-term prognosis of isolated myocardial bridges is generally excellent, but ventricular tachyarrhythmias and sudden cardiac death can occur in high-risk cases 1
Functional assessment is critical: ECG exercise testing, dobutamine stress echocardiography, or myocardial perfusion scintigraphy should be performed to evaluate for inducible ischemia 1, 2
Intracoronary Doppler flow velocity measurement or provocative angiography may be performed in selected cases to obtain functional insight into the hemodynamic significance 1
Management Approach
Beta-blockers are the first-line treatment for symptomatic myocardial bridging, as they reduce heart rate and myocardial contractility, decreasing systolic compression and prolonging diastole for improved coronary perfusion 1, 2
Nitrates are contraindicated because they paradoxically increase angiographic systolic narrowing and worsen symptoms by increasing myocardial contractility 1, 2
For refractory patients who fail medical management with beta-blockers, surgical options include myotomy and/or coronary bypass, while angioplasty or stenting can be considered as alternatives 1
Note: The term "myofascial bridging" in your expanded question refers to a completely different anatomic concept involving muscle and connective tissue connections (such as the myodural bridge between suboccipital muscles and spinal dura mater 3), which is unrelated to cardiac myocardial bridging described above.