What is a myocardial bridge?

Ask the doctor

Q. My 64-year-old brother had some transient chest pain while he was training for a cycling trip, so I urged him to see his doctor. Tests showed that he has a myocardial bridge. What does that mean?

A. The arteries that supply blood to the heart lie on the surface of the organ. But in some people, one of these arteries dives into the heart muscle and comes back out again, forming what's called a myocardial bridge. The bridge refers to the band of heart muscle (myocardium) that extends over that portion of the artery.

This anatomical variation, which is present from birth, is usually harmless. But their prevalence remains a bit uncertain. Myocardial bridges are discovered in fewer than 5% of people who undergo angiography (a procedure that uses a special dye and x-rays to reveal how blood flows through the heart). But in studies of people who undergo more elaborate heart imaging tests, the average prevalence is 25%. And in one autopsy study, half of the cases showed a myocardial bridge.

Most myocardial bridges are found in the heart's largest artery, the left anterior descending artery (see illustration). Most people with this condition never have any symptoms. However, the segment of the blood vessel that is covered by the contracting heart muscle might get squeezed. Occasionally (as could potentially be the case with your brother) this reduces blood flow to the heart muscle — especially during exercise, when the heart is working harder than usual. This can lead to temporary chest pain or discomfort (angina). Less often, people experience more intense symptoms that are similar to those of a heart attack.

When that happens, doctors usually prescribe medications such as beta blockers, which may help by slowing down the heart and making it contract less forcefully. A class of medications called calcium-channel blockers also may be useful, as they can help prevent artery spasm, which can be another unusual cause of chest pain.

People with angina caused by artery-clogging plaque (a much more common cause of angina) sometimes take drugs such as nitroglycerin, which widens the heart's arteries. But for people with a myocardial bridge, nitrates can make their symptoms worse because they can further compress the tunneled artery.

For the very small subset of people with debilitating symptoms that aren't relieved by medication, surgery is an option. The procedure, known as surgical unroofing, cuts through the heart muscle to uncover the tunneled artery. This relieves the compression on the artery and alleviates the symptoms, though it is extremely unusual to need to take this step.

— Deepak L. Bhatt, M.D., M.P.H.
Editor in Chief, Harvard Heart Letter

Illustration by Scott Leighton