What are LIMA (Left Internal Mammary Artery) and LAD (Left Anterior Descending artery)?

LIMA and LAD: Critical Components in Coronary Artery Bypass Grafting

The Left Internal Mammary Artery (LIMA) is the gold standard conduit for bypassing the Left Anterior Descending (LAD) artery during coronary artery bypass grafting (CABG) due to its superior long-term patency and improved patient survival compared to other conduits. 1

What is the LIMA?

• The Left Internal Mammary Artery (LIMA) is an arterial conduit harvested from the chest wall that serves as the preferred bypass graft in CABG surgery 2
• It demonstrates excellent long-term patency rates compared to other conduits such as saphenous vein grafts (SVGs) 1
• When unavailable, the Right Internal Mammary Artery (RIMA) can be used as an alternative to bypass the LAD 1

What is the LAD?

• The Left Anterior Descending (LAD) artery is a major coronary artery that supplies blood to the anterior wall of the left ventricle 1
• It is often referred to as the "widow-maker" due to the high mortality associated with proximal LAD occlusion 1
• Significant stenosis in the LAD, especially in the proximal segment, is a primary indication for revascularization 1

Clinical Importance of LIMA-to-LAD Grafting

• 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 1
• Data from the CASS registry showed improved survival in patients receiving LIMA-to-LAD grafts compared to saphenous vein grafts after multivariable adjustment 1
• Postoperative angiography has demonstrated substantially higher patency rates for LIMA grafts compared to venous conduits 1

Quality Metrics in CABG

• The use of LIMA for LAD bypass is considered a key quality metric in CABG surgery 1
• The American College of Cardiology/American Heart Association measures the percentage of eligible patients who receive an IMA graft (preferably LIMA) when bypass of the LAD is indicated 1
• LIMA usage is now considered a marker of quality control after CABG 2

Special Considerations

• 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
• Sequential LIMA grafting (connecting to multiple coronary targets) can increase the number of arterial grafts and provide more complete arterial revascularization 3
• Certain patient populations have historically received LIMA grafts less frequently, including the elderly (>70 years), females, diabetics, emergency CABG patients, those with poor left ventricular function, and patients with respiratory disease 2

Complications

• Although rare, acute occlusion of the LIMA graft can occur even in the late postoperative period 4
• Unligated LIMA side branches may cause a coronary steal phenomenon, potentially leading to recurrent angina after CABG 5
• Competition between flow through the LIMA graft and native LAD can affect long-term patency, particularly if native vessel stenosis is less severe 6

Clinical Decision Making

• When the LIMA is unavailable or unsuitable, the RIMA is the recommended alternative for LAD bypass 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

The LIMA-to-LAD graft remains the cornerstone of surgical coronary revascularization, providing unmatched long-term benefits in terms of mortality reduction and freedom from reintervention.