What is a myocardial bridge? Cardiology Basics

What is a myocardial bridge? Cardiology Basics

Normally the coronary arteries are located outside the myocardium. Occasionally a segment of the coronary artery passes through the myocardium. This causes a narrowing of that region in systole and is known as myocardial bridging. Myocardial bridging can be recognized as narrowing of a region of the coronary artery in systole which normalizes in diastole.

Usually myocardial bridges do not cause myocardial ischemia as normally the blood flow into the myocardium occur mostly during diastole. Still myocardial bridges can rarely cause  myocardial ischemia and cause chest pain. Rarely this may need recurrent hospital admissions. Very occasionally a myocardial infarction or life threatening ventricular arrhythmias may occur. The risk is more in those with long myocardial bridge associated with coronary vasospasm.

Longer and thicker myocardial bridges may be associated with coronary atherosclerotic plaques. The plaques are noted in locations preceding the region of the myocardial bridge. These partial obstructions can become complete later and cause a myocardial infarction. In this situation the occlusion occurs in a more proximal region of the coronary artery with higher significance.

Generally myocardial bridges are left alone, though in some cases a stent may have to be inserted to prevent the blood vessel from collapsing in systole. It is not a preferred procedure and the results are often unsatisfactory. Stents inserted within myocardial bridges can fracture during systole.

Another option in those with symptoms and objective evidence of myocardial ischemia by investigations, is to bypass the myocardial bridge by a coronary artery bypass surgery (CABG). Bypass grafts to a myocardial bridge can get occluded later as the flow through the native coronary is normal during diastole. Both these options are needed only very rarely for a myocardial bridge. Most myocardial bridges are considered as just incidental finding on coronary angiography.

Another option in those with refractory symptoms is unroofing of the myocardial bridge. When surgery for hypertrophic cardiomyopathy is done, associated myocardial bridges are divided even in children. This gives relief of symptoms which were not responding to medications. In a study of 823 adults who underwent surgery for hypertrophic obstructive cardiomyopathy, some underwent unroofing of myocardial bridge while others underwent coronary artery bypass surgery.

Some were left untreated as well, while others did not have a myocardial bridge. They found similar survival at 3 years in all the four groups. Computed tomography (CT scan) done after 1 year showed that there was no persistence of myocardial bridge after surgical unroofing. The study authors suggested that unroofing of myocardial bridge is the recommended treatment for myocardial bridge and unroofing when technically feasible may be preferable for long term outcome.

In another study using ultrasound probes inside the coronary arteries (intravascular ultrasound, IVUS) it was shown that there was restriction of blood flow even during diastole. Earlier, it was thought that myocardial bridges produce problem only during systole. CT coronary angiography done in these patients also confirmed these findings. This was a group of 111 patients who underwent surgical unroofing of myocardial bridge for symptoms which were not responding to medical treatment. They had limitation of physical activity before surgery, which improved after surgery.

After evaluating 50 patients who underwent myocardial unroofing for myocardial bridges resistant to maximally tolerated medical therapy, another group of authors concluded that it is the optimal treatment for isolated symptomatic myocardial bridges. These patients had undergone extensive multimodality investigation prior to surgery for detailed assessment of the need for surgery. There were no major complications or death in that report.

Different approaches for myocardial bridge unroofing have been described. There are surgeries with and without the use of heart lung machine, surgeries by sternotomy and minimally invasive surgeries without sternotomy. Robotic totally endoscopic unroofing of myocardial bridge without the use of heart lung machine has also been reported.