The internal mammary artery (IMA), also called the internal thoracic artery, is a blood vessel that runs down the inside of the chest wall on each side of the sternum (breastbone). There are two: the left internal mammary artery (LIMA) and the right internal mammary artery (RIMA). These arteries are highly valued as bypass grafts in coronary artery bypass graft (CABG) surgery because of their exceptional long-term durability.
In CABG surgery, the surgeon harvests one or both internal mammary arteries (leaving them attached at their origin from the subclavian artery) and reroutes them to bypass blocked coronary arteries. The LIMA is almost always grafted to the left anterior descending (LAD) coronary artery, the most important coronary vessel, as this combination provides superior patency rates compared to vein grafts. Approximately 90 percent of LIMA-to-LAD grafts remain open at 10 years, compared to around 50 percent for saphenous vein grafts over the same period. This superior durability translates into better long-term survival and reduced need for repeat revascularisation.
The reason for the IMA’s durability relates to its arterial structure and biology: as an artery, it is better adapted to the high-pressure arterial environment of the coronary circulation than a vein graft harvested from the leg. IMA grafts also release nitric oxide, which inhibits the abnormal cell growth (neointimal hyperplasia) that causes vein grafts to narrow and eventually block over time.
Bilateral IMA (BIMA) grafting, using both LIMA and RIMA, provides additional long-term benefit but carries a slightly higher risk of sternal wound healing complications, particularly in patients with diabetes or obesity. For patients who have previously undergone CABG with an IMA graft, any subsequent cardiac arrest investigation or invasive procedure will take account of the altered coronary anatomy created by the bypass surgery.
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