Myocardial bridging is a common congenital anomaly of the coronary arteries where a coronary artery courses through the myocardium.
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Epidemiology
It is found approximately in 20-30% of the adult population in autopsy studies. The incidence in coronary angiograms is between 2-15% and can be easily seen in coronary CT angiography. It occurs more frequently in patients with hypertrophic cardiomyopathy (HCM), and is associated with 12:
increased septal wall thickness
more pronounced left ventricular outflow tract obstruction
Diagnosis
The diagnosis can be conveniently established by typical imaging features on cardiac CT.
Pathology
Normally major coronary arteries follow an epicardial course throughout their length, but in some cases, segments of the coronary arteries may course intramurally into the myocardium (tunneled artery).
Myocardial bridging may be described as:
superficial (incomplete)
deep (complete)
Location
Bridging is typically described for the left anterior descending artery (LAD), with the mid-segment of the LAD considered the most common location 5; however, other major coronary arteries can also be involved 2.
Clinical presentation
Myocardial bridging does not produce any symptoms in the majority of patients. However, conditions which increase the amount of systolic compression (e.g. hypertrophic cardiomyopathy) and/or decrease diastolic filling disproportionately (e.g. rapid heart rates) may exacerbate the myocardial oxygen supply/demand mismatch, resulting in troponin-positive ischemic chest pain with complications such as 12:
arrhythmias
Radiographic features
CT and angiography
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both angiography and coronary artery MDCT can detect LAD myocardial bridging
angiographic diagnosis is by demonstrating an indirect sign called the milking effect
coronary artery CTA directly shows a portion or all of the artery in an intramyocardial location - the length and depth of the tunneled segment along with the location (proximal/mid or distal segment) can be determined on CTCA ref
coronary artery MDCT is often better at detecting RCA myocardial bridging
the bridged segment often appears to be free of atherosclerosis 5; atherosclerotic plaques are most frequently seen in the arterial segment proximal to the tunneled segment of the involved artery ref
MRI
Cardiac MRI including perfusion and MDE sequences can demonstrate
regional wall motion abnormality
perfusion defect about the affected vascular territory (correlates with MPS perfusion abnormality)
T2 hyperintensity and mild T1 delayed myocardial enhancement within the affected vascular territory
Treatment and prognosis
Some reports are suggesting the efficacy of calcium channel blockers in symptomatic patients 3.