The internal mammary artery, also known as the internal thoracic artery (ITA), is a blood vessel within the chest cavity. It is a pair of arteries, with one running on each side of the sternum, or breastbone. Their primary job is to deliver oxygen-rich blood to the structures of the chest wall.
Anatomy and Natural Function
The internal mammary arteries originate from the subclavian arteries, which are large vessels in the upper chest. From their origin near the collarbone, each IMA travels down the inside of the rib cage, running vertically beside the sternum. They are situated between the inner layer of the intercostal muscles and a muscle called the transversus thoracis.
The IMA sends out smaller branches to supply blood to several tissues. These include the sternum, the ribs, the intercostal muscles between the ribs, and the pectoral muscles. It also provides blood to the overlying skin of the chest and the breasts.
Role in Heart Bypass Surgery
The internal mammary artery is a preferred vessel for use as a bypass graft in coronary artery bypass graft (CABG) surgery. A surgeon mobilizes the artery from the chest wall, detaching the lower end while leaving the upper end connected to its origin at the subclavian artery. This keeps the artery “alive” with its own blood supply intact.
The detached end of the IMA is then sewn, or anastomosed, to a coronary artery on the surface of the heart at a point beyond a blockage. This creates a new pathway for blood to flow, bypassing the obstructed section of the coronary artery and restoring circulation to the heart muscle.
The left internal mammary artery (LIMA) is most frequently used to bypass the left anterior descending (LAD) artery. The LAD artery is a major vessel that supplies blood to a large portion of the front and bottom of the heart. The proximity and compatibility of the LIMA to the LAD make this an effective pairing in bypass surgery.
Advantages Over Other Grafts
The IMA holds several advantages over other vessels used for bypass grafts, such as saphenous veins from the leg. The most significant advantage is its superior long-term patency, as IMA grafts are much less likely to become blocked over many years compared to vein grafts.
This durability stems from the artery’s biological properties. As a living arterial vessel, its wall is adapted to the high-pressure flow of the coronary system and is less prone to developing atherosclerosis, the plaque buildup that causes blockages. Vein grafts, in contrast, are not accustomed to arterial pressure and can undergo changes over time that lead to narrowing and failure.
Because the IMA remains attached to its original blood source, it provides a continuous and reliable flow, unlike “free” grafts like veins, which are completely removed and inserted. The cellular structure of the IMA wall is also more resistant to the damage that can lead to graft failure.
Surgical Considerations and Recovery
Surgeons may use both the left and right IMAs in a bilateral IMA (BIMA) bypass. This approach allows for multiple blockages to be bypassed with durable arterial grafts and can be beneficial for younger patients or those with extensive coronary artery disease. The decision to use one or both IMAs depends on the patient’s anatomy and health.
Harvesting the IMA does not compromise blood supply to the chest wall. The body has a redundant circulatory network, and after the IMA is repurposed, other smaller vessels take over to ensure surrounding tissues receive adequate blood flow. Surgeons assess a patient’s risk for sternal wound complications before proceeding with a BIMA.
During recovery, patients can expect discomfort in the chest area, which is part of any open-heart procedure involving the sternum. The use of an IMA itself does not substantially alter the standard recovery process. The focus remains on the gradual healing of the breastbone and a return to normal activities over several weeks to months.