Images

Contrasting appearances on CT images: superficial and flat vs. deep with sharp angle

Myocardial bridges can look very different on images, depending on things like the angles they enter the heart and the different compressions and depths. Below are two examples showing how different these MBs appear. Both are from published studies. One dives into the heart, the other one is more "superficial," pinned to the outside of the heart by a thin band of muscle. But don't let the term superficial fool you: superficial MBs can cause major symptoms. Stanford's surgeon has said "even a paper-thin band of muscle can wreak havoc." Many docs would not even realize that the second image is an MB, because they would be looking for the artery to dive into the heart like the first image.

In the picture on the left, the artery is going into the heart at an unusually sharp angle, almost 90 degrees. Most MBs do not go in at nearly this steep of an angle. You can also see how the artery gets fuzzier when it goes in the heart, which can be because of a motion blur since the artery is moving in there i.e. getting squashed as the MB compresses each heartbeat.

The second picture shows a superficial MB, which again can still cause major symptoms. Some signs that show it is clearly an MB are that there is no black (fat) between the artery and the heart (gray) in the MB area, and the artery gets fuzzier/blurrier in the MB area.

MDCT - Multidetector Computed Tomography
Source: Left anterior descending coronary artery myocardial bridging by multislice computed tomography: Correlation with clinical findings, Jodocy et al

Multidetector computed tomography or MDCT images are 3D images created by combining many individual slices (up to 300+). MDCT images have revolutionized the evaluation of MBs. Before, cardiac catheterizations (or "caths") were considered to be the standard in detecting MBs. But there are major drawbacks to using caths, including: 1) they identify MBs indirectly, by a "milking effect," which sometimes does not appear when MBs are shallow or superficial, and 2) caths often underestimate the length of MBs.

MDCT images, however, give a view of the actual physical anatomy of the MB itself. With deeper MBs, they can show the actual band of muscle going over the artery and the artery disappearing into the heart. With shallower, more superficial MBs, they can show a subtle dipping of the artery just below the heart surface, covered by a thin layer of muscle.

IVUS Cath images of the "VA" - vessel area - as the heart squeezes (systole) and relaxes (diastole)
Source: Myocardial Bridge and Acute Plaque Rupture, Perl et al

Every time a heart squeezes, the myocardial bridge compresses the artery, like stepping on a garden hose. This makes the cross-sectional area of the artery smaller. This is called the vessel area, or VA in the images above. In these images, the opening in the artery (like the hole in a donut), called the "lumen," clearly gets smaller on the right as the MB squeezes down during systole. So the calculated VA gets smaller, from 7.55 mm² to 5.72 mm², which the subtitle shows is a difference of 24.2%. In other words, 24.2% of the space for blood to flow through the artery is lost when the heart squeezes. In some people, the compression of the MB on the artery can be so high that the VA drops to zero, leaving no space for blood to flow through. This is one reason MBs can cause heart attacks.

Also, right alongside the lumen (the hole in the middle), you can see a black half-moon shape. Technically called the "halo sign" or "echolucent half-moon sign," this is the MB itself pressing down on the outer wall of the artery.

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