Taking Down The LIMA
Editor’s Note:
Routine CABG is like a theater or an opera. There are many subsets of acts and scenes. One of the most common segments in the land of perfusion- is that narrow window of 20 or so minutes (sometimes longer – sigh) where the OR is in a calm reflective state as the surgeon sits down and dissects out the Left Internal Mammary Artery (LIMA) sometimes referred to as the Internal Thoracic Artery.
This is the brief oasis of time where you can scarf down a quick cup of coffee, check your email, do last minute checks on your setup, or call whomever about whatever.
I thought about it yesterday, and feel like we all take his “respite” for granted, and the only one really working happens to be the CV surgeon.
So to honor this event and and the associated humble yet seriously important vessel, here is a closer view of what we are doing, and why it’s so important.
Revascularization with the ITA
The internal thoracic artery is the cardiac surgeon’s blood vessel of choice for coronary artery bypass grafting. The left ITA has a superior long-term patency to saphenous vein grafts[1][2] and other arterial grafts[3] (e.g. radial artery, gastroepiploic artery) when grafted to the left anterior descending coronary artery, generally the most important vessel, clinically, to revascularize.
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The Internal Mammary Artery
Mark M. Levinson, MD
Hutchinson Hospital, Hutchinson Kansas
The Internal Mammary Artery (IMA) is a blood vessel located on the inside of the chest cavity. It is an artery, not a vein. thus it carries red blood under the same blood pressure as that seen in the aorta or the coronary arteries themselves. There is one IMA on each side of the breastbone (aka sternum). This unique blood vessel runs along the inside edge of the sternum, sending off small branches to the bones, cartilage, and soft tissues of the chest wall. For unclear reasons, the IMA is remarkably resistant to cholesterol buildup. In studies of people who die beyound the age of 90, only 10% will show any atherosclerosis in the IMA vessels, while nearly all such individuals have atherosclerosis in the coronary arteries and other places. The reasons for mammary artery’s resistance to atherosclerosis is not known at present.
The IMA is also conveniently located near the most important coronary branch, the left anterior descending (LAD). The surgeon can transfer the lower end of the IMA down to the heart surface to use as a bypass graft to the coronary vessels. As compared to the veins from the lower extremity, the IMA is smaller and more delicate. However, studies have shown that the use of the left internal mammary artery (LIMA) is associated with improved long term results from coronary artery bypass surgery. In most places around the world, surgeons implant the LIMA into the LAD whenever possible. Sometimes the LIMA is too small to use. And in other cases, the vessel is so delicate that just the steps taken to remove if from underneath the ribs will cause harm to the vessel wall, making the IMA useless. However, in about 90% of coronary bypass operations, this vessel is the best conduit available for surgical bypass to the major arteries of the heart.
Kolessov, a Russian surgeon living in Leningrad, was the first person to connect the internal mammary artery (IMA) to the coronary artery for the purposes of relieving angina. His intrepid efforts were mostly ignored by the surgical community for many years. During the early development of coronary bypass surgery, the greater saphenous vein (GSV) from the lower extremity was utilized by most surgeons because it was:
- Quick and easy to harvest,
- Always long enough,
- Stronger tissue and not as delicate at the IMA, and
- Larger in caliber than the IMA, making surgery technically easier.
However, through the ceaseless efforts of some committed surgeons, most notably Dr. George Green of New York, the advantages of using the IMA for CABG surgery became clear. As experience with LIMA grafting grew, Dr. Greens predictions for longevity proved correct. The patients with LIMA grafts enjoyed better long-term results when compared with patients receiving only vein grafts.
