Atherosclerosis of the Internal Mammary Artery: Intravascular Ultrasound and Virtual Histology Imaging

J INVASIVE CARDIOL 2018;30(4):E35-E36.

Key words: cardiac imaging, atherosclerosis

Internal mammary artery (IMA) bypass grafts have been associated with better long-term survival compared to saphenous vein grafts (SVGs). Early IMA graft failure is considered to be from poor surgical technique and less from thrombosis. Atherosclerotic changes in the IMA are rare and are usually described as small focal infiltrates of lipid in the intima. Structurally, its endothelial layer shows fewer fenestrations, lower intercellular junction permeability, greater antithrombotic molecules such as heparin sulfate and tissue plasminogen activator, and higher endothelial nitric oxide production, which are some of the unique ways that make the IMA impervious to the transfer of lipoproteins, which are responsible for the development of atherosclerosis.

A 61-year-old male was admitted with ongoing chest pain, shortness of breath, and diaphoresis for 2 hours. Electrocardiogram (ECG) revealed ST elevation in lead AVR with ST depression of 2 mm in inferior lateral leads. His past history was positive for smoking. Cardiac catheterization revealed chronically occluded right coronary artery (RCA) and subtotal occlusion of the distal left main coronary artery. In view of his ongoing symptoms, he underwent intraaortic balloon pump insertion and emergent coronary artery bypass graft surgery with left IMA bypass graft to the left anterior descending (LAD) and SVG to the obtuse marginal (OM) artery and RCA. During postoperative day 1, the patient needed to be on high doses of intravenous inotropic drugs. ECG continued to have significant ST changes. Repeat cardiac catheterization showed patent SVG graft to the RCA and OM and patent IMA to the LAD; however, the proximal segment of the IMA shaft had a focal 70%-75% stenosis. After administering nitroglycerin, angiography still showed the same disease. Intravascular ultrasound of the IMA then revealed significant stenosis (cross-sectional area of the diseased segment was 2.5 mm² and the proximal normal segment was 8.5 mm²).Virtual histology was performed, and revealed fibrofatty and predominantly necrotic plaque burden. The heart team then decided on stenting of the IMA graft to the LAD with a single Synergy drug-eluting stent (Boston Scientific). Electrocardiography performed the next day revealed improvement in the ST-segment depression and the patient improved hemodynamically and was discharged home.

Atherosclerotic disease of the IMA shaft is rare. Angiography or arterial duplex ultrasound before bypass surgery of the IMA should be performed even when considering the patient for an emergent bypass surgery.

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From Carle Foundation Hospital, University of Illinois at Urbana-Champaign, Urbana, Illinois.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript accepted October 13, 2017. 

Address for correspondence: Sanjay S. Mehta, MD, FACC, FSCAI, Assistant Professor of Medicine, Carle Foundation Hospital, University of Illinois at Urbana-Champaign, 611 W. Park Street, Urbana, IL 61801. Email: Sanjay.Mehta@Carle.com