What is a LIMA (Left Internal Mammary Artery)?
The Left Internal Mammary Artery (LIMA) is the gold standard blood vessel conduit used in coronary artery bypass grafting (CABG) surgery, primarily to bypass blockages in the Left Anterior Descending (LAD) artery, with superior long-term patency rates exceeding 90% at 10-15 years. 1, 2
Anatomical Location
- The LIMA is located in the anterior mediastinum, positioned anterior to the pericardium and heart, making it readily accessible during median sternotomy for cardiac surgery 1
- It is harvested either as a pedicled graft (with surrounding tissue) or as a skeletonized graft (vessel alone), then brought down to reach the heart surface for anastomosis to the LAD 1
Why LIMA is the Gold Standard
- LIMA-to-LAD grafting is a Class I recommendation (Level of Evidence: B) in coronary artery bypass surgery 1
- The LIMA demonstrates >90% patency at 10-15 years, vastly superior to saphenous vein grafts which show only 50-60% patency at 10 years 1, 2
- Use of LIMA significantly reduces mortality, recurrent myocardial infarction, rehospitalization for cardiac events, and need for repeat revascularization compared to other conduits 1
Clinical Indications for LIMA Use
- Patients with diabetes and multivessel disease including hemodynamically significant LAD disease should receive CABG with LIMA-to-LAD over percutaneous coronary intervention (PCI) 1
- Patients with complex 3-vessel coronary artery disease (especially with SYNTAX score >22) benefit from CABG with LIMA-to-LAD over PCI 1
- Patients with left main disease have particularly strong evidence supporting CABG with LIMA-to-LAD 1
- For redo CABG procedures, LIMA is the conduit of choice in patients who did not receive LIMA previously 1
Critical Technical Considerations
- The LIMA should only be used to bypass vessels with adequate stenosis severity—at least 70% for left-sided vessels including the LAD—to avoid competitive flow-related graft failure 3
- Arterial grafts like LIMA are muscular conduits that respond to low-flow states with vasospasm and eventual atrophy when competitive flow exists 3
- Large LIMA side branches should be ligated during surgery to prevent coronary steal phenomenon, which can cause postoperative angina 4
Contraindications and When Not to Use LIMA
- Significant proximal left subclavian stenosis is an absolute contraindication to LIMA use, as it would compromise flow through the graft 1
- When LIMA is unavailable or unsuitable, the right internal mammary artery (RIMA) is the recommended alternative for LAD bypass 1
Quality Measure
- The American College of Cardiology/American Heart Association measures the percentage of eligible patients who receive an internal mammary artery graft (preferably LIMA) when bypass of the LAD is indicated as a quality control metric 1, 5
- LIMA usage rates of >90% are considered the benchmark for quality CABG programs 5