A Bridge Over Troubled Arteries: Myocardial Bridging Presenting as Acute Coronary Syndrome

Abstract

A myocardial bridge is a congenital band of heart muscle that lies on top of a coronary artery, instead of underneath it. Part of a coronary artery dips into and underneath the heart muscle bridge, and then comes back out again. During systole, the bridge can tighten down on the artery, pinching it and decreasing the blood flow. CASE PRESENTATION: A 39-year-old presented with acute pulmonary edema after undergoing elective laparoscopic appendectomy. After surgery, he desaturated to 85%, along with hypotension and bradycardia. ECG showed normal sinus rhythm at 66 BPM with 1mm ST elevations in I, aVL, and V2-6. Troponin I was 2.85. Echocardiogram revealed low normal EF and lateral wall motion abnormalities. Coronary angiography (CA) showed EF 55% with distal LAD artery myocardial bridge (Figure 1). He was discharged on aspirin and beta-blocker. The second case was a 67-years-old female who was admitted for chest pain and found to have inferior wall NSTEMI. CA showed 99% stenosis of distal LCA with grade II flow. A stent was placed and she was discharged on aspirin, clopidogrel and statin. Nine days later, she presented with recurrent chest pain, dyspnea and fatigue. Vitals were stable and ECG was similar to that from prior discharge. A repeat CA showed patent LCA stent, with systolic compression of LAD artery. She did not require further intervention and was transferred to the telemetry unit where she remained chest pain free and hemodynamically stable for 48 hours. DISCUSSION: Although myocardial bridging is a systolic phenomenon, arterial compression with over 70% arterial lumen reduction can result in myocardial ischemia, arrhythmia, depressed LV function, myocardial stunning and SCD. Atherosclerosis preferentially develops immediately proximal to the bridged segment, possibly due to shear stress, while the compressed segment itself is often spared. It is therefore important to treat these patients with beta-blockers and antiplatelet therapy. Surgical myotomy, intracoronary stenting, and CABG have been used for refractory symptoms, but long-term outcomes remain uncertain. CONCLUSIONS: Physicians should be aware of myocardial bridge as an independent risk factor for coronary artery atherosclerosis.