What is a LIMA (Left Internal Mammary Artery)?
The Left Internal Mammary Artery (LIMA) is the gold standard blood vessel conduit used during coronary artery bypass grafting (CABG) surgery, particularly for bypassing the left anterior descending (LAD) artery, due to its superior long-term patency rates exceeding 90% at 10-15 years. 1
Anatomical Location and Surgical Access
- 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
- During CABG, the LIMA 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
- Its proximity to the LAD artery makes it the ideal conduit for LAD revascularization 1
Clinical Superiority and Outcomes
- LIMA grafting to the LAD is a Class I recommendation (Level of Evidence: B) in coronary artery bypass surgery 1
- The use of LIMA for LAD bypass significantly reduces mortality, recurrent myocardial infarction, rehospitalization for cardiac events, and the need for repeat revascularization compared to other conduits 1
- LIMA demonstrates superior long-term patency compared to saphenous vein grafts, which have only 50-60% patency at 10 years 2
- The American College of Cardiology 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 metric 1
Specific Clinical Indications
- In patients with diabetes and multivessel disease including hemodynamically significant LAD disease, CABG with LIMA-to-LAD is preferred over percutaneous coronary intervention (PCI) 1
- For patients with complex 3-vessel coronary artery disease (especially with SYNTAX score >22), CABG with LIMA-to-LAD is preferred over PCI 1
- In patients with left main disease, the evidence supporting CABG with LIMA-to-LAD is particularly strong 1
- For redo CABG procedures, LIMA is indicated as the conduit of choice in patients in whom the LIMA was not used previously 3
Critical Technical Considerations
- LIMA should only be used to bypass vessels with adequate stenosis severity—at least 70% stenosis for left-sided vessels—to avoid competitive flow-related graft failure 4
- Arterial grafts like LIMA are muscular conduits that respond to low-flow states with vasospasm and eventual atrophy when competitive flow is present 4
- Significant proximal left subclavian stenosis is a contraindication to LIMA use, as it would compromise flow through the graft 1
- Large LIMA side branches should be ligated during surgery to prevent coronary steal phenomenon, which can cause postoperative angina 5
Common Pitfalls to Avoid
- Never use LIMA to bypass vessels without adequate stenosis severity, as competitive flow will promote graft failure 4
- Ensure target vessels have appropriate stenosis: LAD and left-sided vessels should have ≥70% stenosis for arterial grafting 4
- When LIMA is unavailable or unsuitable, the right internal mammary artery (RIMA) is the recommended alternative for LAD bypass 1