Left Anterior Descending Coronary Artery Muscular Bridge

A 50-year-old man with no history of cardiac disease presented with progressive dyspnea. Results of a physical examination and a resting electrocardiogram were normal. An electrocardiogram during exercise showed nonspecific ST-segment changes in the anterior chest derivations. Transthoracic echocardiography revealed hyperdynamic left ventricular systolic function. Subsequent myocardial perfusion scintigraphy confirmed ischemia of the anteroapical wall of the left ventricle and interventricular septum. Coronary angiography showed a complete myocardial muscular bridge of the left anterior descending coronary artery (LAD), with pulsatile contrast hanging or a “milking effect.” Dynamic compression of the proximal and mid segments of the LAD was observed during systole (Fig. 1A) and diastole (Fig. 1B). The coronary tree showed no angiographic signs of atherosclerosis. Despite therapy with aspirin, a β-blocker, and a calcium antagonist, the patient experienced dyspnea during exercise, so supra-arterial decompression myotomy was planned. With the patient under cardiopulmonary bypass and cardiac arrest, the proximal and mid segments of the LAD were exposed by means of sharp dissection. We observed that the tunneled 6-cm segment of the vessel was completely between the hypertrophic muscle bands (Fig. 2). The bridge was at a depth of almost 4 mm. Supra-arterial debridging was performed. After one month, a coronary angiogram showed no stenosis along the LAD during systole or diastole (Fig. 3).

Fig. 1 Coronary angiograms show dynamic compression of the proximal and mid segments of the left anterior descending coronary artery during A) systole (arrows indicate the start, midpoint, and end of the myocardial bridge), and B) diastole.

Real-time motion image is available at www.texasheart.org/journal.

Fig. 2 Intraoperative photographs. A) The muscular tunnel extends over the left anterior descending coronary artery for 6 cm, involving its proximal and mid segments (the whole distance was divided into 6 equal parts, denoted by white dots on the ruler). B) This area was opened, and the left anterior descending coronary artery (arrow) was decompressed.

Fig. 3 Coronary angiograms after supra-arterial debridging show no compression along the left anterior descending coronary artery in A) systole or B) diastole.

Real-time motion image is available at www.texasheart.org/journal.

Comment

Myocardial bridging is anatomically defined as muscle that overlies the intramural segment of a major epicardial coronary artery. Myocardial bridges are classified as complete or incomplete. In complete myocardial bridging, the tunneled artery is completely surrounded by a band of myocardial muscle. In contrast, incomplete bridges are covered partly by myocardial fibers and partly by a thin layer of connective tissue. A myocardial bridge generally presents with segmental involvement of the coronary arteries and results in dynamic stenosis due to systolic compression.¹ Involvement of more than one segment of the LAD is rare in muscular bridging. In our patient, the proximal and mid segments of the LAD were involved, and the artery was completely surrounded by muscular tissue. Although most patients are clinically asymptomatic, sequelae of complete muscular bridging in the LAD can include ischemia, acute coronary syndrome, coronary spasm, arrhythmia, or sudden death. In patients with myocardial ischemia, coronary angiography is an excellent imaging method because it enables the evaluation of dynamic changes in coronary flow during systole and diastole. Computed tomographic coronary angiography yields direct views of the bridge itself and can enable differentiation between complete and incomplete bridges.^2,3 Surgical supra-arterial myotomy is the debridging procedure of choice to prevent myocardial infarction and sudden death in patients who remain symptomatic despite medical treatment.²