Myocardial Bridging

Myocardial bridging refers to an anatomic variant where a short segment of a coronary artery dips into and is completely surrounded by myocardium. As would be expected, this segment narrows during systole and re-expands during diastole. It is most commonly seen in the left anterior descending coronary artery.

Myocardial bridging is easily detected on conventional angiography, which reveals a characteristic "milking" appearance: The lumen of the arterial segment is compressed by myocardial contraction during systole but recovers its normal diameter in diastole.

On CT coronary angiography, however, myocardial bridging may be mistaken for focal stenosis. Multiplanar reformations help by depicting myocardial fibers overlying the arterial segment.

The bridged segment rarely has atherosclerosis, but plaques may be seen proximally and distally. Chest pain and myocardial infarction may occur if there is >75% narrowing during systole.

Septal perforating arteries, which are normally intramural, don't narrow much during systole unless there is increased left ventricular wall tension (e.g., as may be seen with aortic stenosis, hypertensive heart disease, and hypertrophic cardiomyopathy).

References

• Choi HS, Choi BW, Choe KO, Choi D, Yoo KJ, Kim MI, Kim J. Pitfalls, artifacts, and remedies in multi- detector row CT coronary angiography. Radiographics. 2004 May-Jun;24(3):787-800.
• Miller SW and Boxt LM. Chapter 7: Ischemic heart disease. in Cardiac Imaging: The Requisites (third ed). Miller SW et al (eds).