Dr Arvind Kohli
Coronary artery bypass is the process of restoring the flow of blood to the heart. The surgical procedure places new blood vessels around existing blockages in the coronary arteries to restore necessary blood flow to the heart muscle. Once blood flow is re-established normal heart function may return in time.
The most common type of revascularization procedure is Coronary Artery Bypass Grafting,called CABG (“cabbage”). which involves use of at least one artery from inside the chest (the internal mammary done through the same chest incision called LIMA). and the other conduit is saphenous vein from the leg. For patients with multivessel coronary disease undergoing what is usually referred to as conventional CABG, the LIMA is typically grafted to the left anterior descending (LAD) artery with saphenous vein grafts often used to bypass the remaining coronary occlusions.
When total arterial revascularization (TACR) is used for coronary artery bypass grafting (CABG) surgery, only .arterial conduits are now being more frequently used as choices for the second and third conduits in place of saphenous vein grafts to achieve total arterial revascularization (TAR) of the myocardium due to superior patency and long-term survival results..
Various studies has shown that more people with diabetes survive when only arteries are used for bypasses during CABG surgery. People with diabetes also experience fewer long-term complications from TACR/CABG than from conventional CABG. As a result, there is room for a much larger proportion of people to have this type of coronary surgery and receive the benefits of a longer life, better quality of life and reduced medical costs.
Various arterial conduits which are being commonly used these days for TACR are following :
LIMA The use of the left internal mammary artery (LIMA) is widely considered to be the gold standard for conventional CABG operations The use of the left internal mammary artery (LIMA) is widely considered to be the gold standard for conventional CABG operations. Its use has been shown to result in a lower incidence of reintervention, fewer myocardial infarctions, a lower incidence of angina, and lower associated mortality rates than with the use of saphenous vein grafts alone. Also when compared to saphenous vein grafts, LIMA use has been shown to have greater long-term patency results
RIMA (Right Internal Mammary artery) While anatomically identical to the LIMA, the RIMA is rarely used in CABG procedures, and is almost always used as part of bilateral internal mammary artery (BIMA) grafts when it is utilized. . Reasons for not using the RIMA include increased operative time and perceived technical difficulty associated with the harvest, concern for perioperative morbidity and mortality, the possibility of reoperations for bleeding, sternal wound infection, .
LIMA RIMA Y/T There are a variety of grafting techniques for BIMA, such as in situ grafting versus Y/T-grafts that may have an impact on patency rates. .
Radial Artery The radial artery has been a popular choice as an additional arterial conduit in attempts to achieve total arterial revascularization of the myocardium. There are numerous advantages to using the radial artery, including its long length, exposure to systemic blood pressures, and the fact that it is seldomly affected by atherosclerosis. However, the radial artery has a thicker tunica media, which is thought to contribute to its greater vasoconstrictor response than the IMA and could possibly lead to vessel occlusion. Thus, care must be taken during operative harvesting and the use of calcium-channel blockers may ameliorate a vasospastic response
Right Gastroepiploic artery use has also been mentioned as a conduit for arterial graft
Graft Combinations a final assessment is made before committing to the final grafting strategy. The heart and target coronary arteries are inspected and the Internal mammary artery caliber and length is assessed. For patients requiring left-sided grafts . BIMA is used, either in situ (using RIMA to main left sided coronary artery known as LAD LIMA to lateral wall coronary artery known as Circumflex) or as a “T” graft (LIMA to LAD; RIMA to lateral wall). The use of two IMAs for all patients is obviously ideal, but its good to use a LIMA/radial “T” graft for very elderly or morbidly obese patients requiring three vessel revascularizations, thus reducing operative times and potential morbidity.
Conclusion
Poor long-term patencies of saphenous vein grafts coupled with the greater long term patency results of the LIMA as the gold standard conduit for CABG has prompted surgeons to seek out additional arterial conduits . Achieving total arterial revascularization of the myocardium would then be a natural progression for the procedure. Since it is anatomically identical to the LIMA, the RIMA would be the next logical choice in arterial conduits, yet is rarely used in CABG operations due to the perceived technical difficulty of harvest and increased operating times, a higher risk of developing sternal bone wound infections However its use as BIMA has been beneficial
The radial artery is also a suitable conduit to use in conjunction with BIMA or as a second arterial conduit if either the LIMA or RIMA is not suitable for use. Guidelines for Coronary Artery Revascularization have recommended the use of a LIMA to the LAD and arterial grafts to the non-LAD system in patients with a reasonable life expectancy, with minimization of aortic manipulation where possible. The use of bilateral internal mammary arteries (BIMA) makes the adherence to these recommendations easier.
(The author is Cardiac Surgeon SSH Jammu)
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