BRIDGING THE GAP: CTA AND IVUS OF THE HEART
A myocardical bridge is an abnormality that is caused by a band of muscle that lies on top of a coronary artery, instead of being beneath it. You can imagine this like a thread going through a piece of cloth. Usually, this condition is benign, and doesn’t cause any discomfort to the patient. There are however, cases written in medical literature of patients developing myocardial ischemia, which is caused by a lack of oxygen reaching the heart muscle, and various life-threatening acute coronary syndromes. The band of muscle can squeeze or narrow the coronary artery and consequently blood flow is restricted. This condition is something you’re born with, so you may not know about it until you either have symptoms, or you undergo diagnostics for unrelated conditions during which myocardial bridging is found. Myocardial bridges can be treated using beta-blockers or calcium channel blockers, as the first-line treatment, and in rare cases, surgery may be needed.
Myocardical bridging of the LAD (left anterior descending) coronary artery
CTA or IVUS – which is better?
CTA (computed tomography angiography) is currently the gold standard for evaluating myocardial bridging, because it‘s highly accurate. However, recent research has shown that CTA is not all-seeing and all-knowing. IVUS (intravascular ultrasound) may be the better choice.
The study included 64 patients with symptoms of ischemia who underwent both CTA and IVUS. CTA earned its gold star, but surprisingly missed the majority of septal branches and soft plaques that could potentially cause serious complications.
Lead author Dr. Hans-Christoph Becker stated that, "Over the years, the heart may change in a way that there's ventricular hypertrophy present, as well as diastolic dysfunction and endothelial dysfunction," and added that "All these lead to the fact that blood flow may be altered in a way so that myocardial ischemia may be present during the development of changes within the myocardium."
There are a few interesting facts about myocardial bridges that should be highlighted. Atherosclerotic (a condition where arterial walls thicken due to plaque) lesions never form within a bridge, only in front or behind it. This phenomenon is thought to be related to flow dynamics. Another interesting point is that bridging can occur in many places and in varying degrees, which can be evidenced by a thickening of the myocardial wall surrounding a coronary artery.
IVUS-images of the myocardial bridge during diastole (left) and systole (right). A “half-moon”–like area surrounding the tunneled segment is present during the entire cardiac cycle.
On IVUS, there are specific signs that are characteristic of bridging and include a specific, echolucent half-moon phenomenon over the bridge segment, which exists throughout the cardiac cycle; accelerated flow velocity at early diastole (the part of the cardiac cycle when the heart is refilled with blood) (fingertip phenomenon).
The study showed that both modalities are very effective and correlate with each other very well, but CTA was found to have a few weaknesses. Only 75.4% of septal branches in IVUS were also seen in CTA, and noncalcified plaques cannot be seen in CTA.
Is there a clear winner?
If one considers all the strengths and weaknesses, CTA still comes out on top. It’s noninvasive, safer and highly accurate. IVUS may be able to see a bit more, but it’s an invasive procedure with higher risks for the patient.
This author is certain that with improvements to CTA, particularly the ability to visualize soft plaques, it will cement its place as the perfect method for all things coronary.
Ge J, Jeremias A, Rupp A, Abels M, Baumgart D, Liu F, Haude M, Görge G, von Birgelen C, Sack S, Erbel R. New signs characteristic of myocardial bridging demonstrated by intracoronary ultrasound and Doppler. Eur Heart J. 1999 Dec;20(23):1707-16. PubMed PMID: 10562478.
Case courtesy of Robin Smithuis and Tineke Willems
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