Coronary artery bypass surgery conduits used for bypass

The choice of conduits (arteries and/or veins from elsewhere in the body) to bypass the blockages is highly surgeon and institution dependent. To choose the proper conduits for CABG both clinical and technical factors such as life expectancy, presence of diabetes, chronic renal failure, and degree of the target stenosis must be considered. Saphenous vein, internal thoracic artery, and radial artery are the most used vessels to harvest for grafting. The saphenous vein can be harvested by either direct visualization or via an endoscopic approach. Among these two methods the endoscopic approach has been associated with lower rates of wound infection, greater patient satisfaction, and earlier mobilization. However, non-randomized data from a much larger multicenter study does suggest that endoscopyendoscopic harvesting may be associated with a higher rate of failure and adverse events such as death and MI. Veins that are used either have their valves removed or are turned around so that the valves in them do not occlude blood flow in the graft. On the other hand, numerous studies support the use of the left internal thoracic artery (LITA) (also known as the left internal mammary artery (LIMA)) to graft the LAD in order to improve survival unless contraindicated. Evidence shows that the right IMA can be used to graft the LAD if the LIMA is impractical and unusable. Furthermore, the right IMA can be used in conjunction with the LIMA which is called bilateral internal mammary artery (BIMA) grafting. The latter method showed a better outcome based on multiple studies. In multiple arterial revascularization during Coronary artery bypass surgery, the right internal thoracic artery (RITA) has been proofed to be a better choice as a conduit than the radial artery. On the other hand, numerous clinical trials have demonstrated better patency rates (in mid- and long-term) when the radial artery is used in comparison with the saphenous vein.

• The choice of conduits (arteries and/or veins from elsewhere in the body) to bypass the blockages is highly surgeon and institution dependent.
• To choose the proper conduits for CABG both clinical and technical factors such as life expectancy, presence of diabetes, chronic renal failure, and degree of the target stenosis must be considered.^[1]
• The following table published by 2021 ACA Revascularization Guideline presents the best practices for the Use of bypass conduits in CABG:^[1]

• Typically, the left internal thoracic artery (LITA) (also referred to as the left internal mammary artery or LIMA) is grafted to the Left Anterior Descending artery and a combination of other arteries and veins is used for other coronary arteries.
• The right internal thoracic artery (RITA), the great saphenous vein from the leg and the radial artery from the forearm are frequently used.
• The right gastroepiploic artery from the stomach is infrequently used given the difficult mobilization from the abdomen.

• The great saphenous vein (GSV) is frequently used as a conduit for CABG. It originates from where the dorsal vein of the first digit (the large toe) merges with the dorsal venous arch of the foot.
• After passing anterior to the medial malleolus (where it often can be visualized and palpated), it runs up the medial side of the leg. At knee, it runs over the posterior border of the medial epicondyle of the femur bone.
• The great saphenous vein then courses laterally to lie on the anterior surface of the thigh before entering an opening in the fascia lata called the saphenous opening. It joins with the femoral vein in the region of the femoral triangle at the saphenofemoral junction.
• The small saphenous vein (also lesser saphenous vein) originates where the dorsal vein from the fifth digit (smallest toe) merges with the [[dorsal venous arch of the foot, which attaches to the great saphenous vein. It is considered a superficial vein and is subcutaneous (just under the skin). From its origin, it courses around the lateral aspect of the foot (inferior and posterior to the lateral malleolus) and runs along the posterior aspect of the leg (with the sural nerve), passes between the heads of the gastrocnemius muscle, and drains into the popliteal vein, approximately at or above the level of the knee joint.

• 
  Cross-section through the middle of the thigh.
• 
  Cross-section through the middle of the leg.
• 
  The great saphenous vein and landmarks along its course
• 
  The great saphenous vein and its tributaries at the fossa ovalis in the groin.
• 
  Small saphenous vein and its tributaries.

• The saphenous vein can be harvested by either direct visualization or via an endoscopic approach. Veins that are used either have their valves removed or are turned around so that the valves in them do not occlude blood flow in the graft. The technique of saphenous vein harvesting may influence later SVG patency. The process of harvesting the vein and pressure testing the vein for a leak may damage the endothelium.^[2][3]
• The endoscopic approach has been associated with lower rates of wound infection, greater patient satisfaction, and earlier mobilization.^[4][5][6][7] One small randomized study of 144 patients showed no difference in histologic findings between the traditional and endoscopic techniques.^[4]In another small study of 40 patients randomized to the two techniques, no difference was seen in angiographic patency at 3 months.^[7]Another small randomized study of 144 patients who returned for angiography demonstrated an occlusion rate of 21.7% for the endoscopic approach vs 17.6% for the open approach.^[6]
• However, non-randomized data from a much larger multicenter study does suggest that endoscopyendoscopic harvesting may be associated with a higher rate of failure and adverse events such as death and MI.^[5]
• Complications associated with saphenous vein harvesting include the following:
  • Saphenous nerve injury
  • Infection at incision sites or sepsis.
  • Deep vein thrombosis (DVT)
  • Keloid scarring
  • Chronic pain at incision sites

• Numerous studies support the use of the left internal thoracic artery (LITA) (also known as the left internal mammary artery (LIMA)) to graft the LAD in order to improve survival unless contraindicated.^{[1][8][9][10]}
• In a study evaluating almost 6,000 patients, LIMA grafting was able to reduce the rate of cardiac-related rehospitalization and revascularization. In addition, this study showed a lower rate of death and recurrent infarction in those who undergone LIMA grafting.^[11]
• Evidence shows that the right IMA can be used to graft the LAD if the LIMA is impractical and unusable. Furthermore, the right IMA can be used in conjunction with the LIMA which is called bilateral internal mammary artery (BIMA) grafting.^[1]
  • Based on observational studies, BIMA grafting has a survival advantage when compared with CABG with a single IMA.^{[1][12][13][14][15]}
  • Reports from a meta-analysis of 38 studies, including 174,205 patients demonstrated a decreased mortality rate at 7.25 years follow up among patients who had BIMA grafting.^[15]
  • On the other hand, a single large randomized controlled trial reported no difference in 10-year all-cause mortality when BIMA was compared with single IMA. Furthermore, this study highlighted the importance of surgical expertise in BIMA grafting.^[16]
  • It is critical to consider the higher risk of sternal infection with BIMA grafting.^[17]
• In multiple arterial revascularization during Coronary artery bypass surgery, the right internal thoracic artery (RITA) has been proofed to be a better choice as a conduit than the radial artery. This has been published at the European Society of Cardiology (ESC) 2011 Congress, after a trial on more than 1000 patients who had the operation in 10 years trial.
• The left internal thoracic artery (LITA) (also known as the left internal mammary artery (LIMA)) is the best vessel to use for coronary artery bypass surgery when only one artery is required.
  • It was known that the long-term outcomes of the arterial grafts are much better than saphenous vein grafts (SVGs) and has less morbidity and mortality rates.^{[18][11][9][10]}
  • The right internal thoracic artery (RITA) is the best second conduit for the bypass and has better long-term outcomes than the radial artery. The use of the RITA results in the following in comparison with SVG:
    • Less major adverse cardiac and cerebrovascular events.
    • Less perioperative myocardial infarction rates.
    • Less perioperative stroke rates.
    • Less cardiac-related deaths.
• There have been good clinical results with the single left internal thoracic artery grafting compared with saphenous vein grafting. This prompted surgeons to use both ITAs. Bilateral ITA grafting could improve long-term survival. Late complications like myocardial infarction and need to reoperate may be avoided. However, mathematical modeling is required to assist in developing a strategy for use of such grafts.^[19]
• In a cohort study of 8123 patients who received single internal thoracic artery grafts and 2001 who received bilateral internal thoracic artery grafts for multivessel coronary artery disease for a duration of 20 years, it was found that the latter produces improved survival compared with single internal thoracic artery grafting during the second postoperative decade, and the magnitude of that benefit increases through 20 postoperative years.^[20]
• It’s easy to harvest the radial artery, but it has a higher risk for vasospasm and atherosclerosis than the right internal thoracic artery (RITA). Some institution solves this problem (vasospasm) by preparing the radial arteries with phenoxybenzamine.
• Although the fact that using both internal thoracic arteries for coronary artery bypass surgery takes a longer time, it has better long-term results and perioperative outcomes. This has to be proofed and confirmed by more randomized and controlled trials.

• Numerous clinical trials have demonstrated better patency rates (in mid- and long-term) when the radial artery is used in comparison with the saphenous vein.^[21][22][23]
• Furthermore, several observational studies reported a better survival rate when the radial artery is used instead of the saphenous vein for CABG.^[12][24][21]
• Based on the 2021 ACA Revascularization guideline, the following patients benefit the most from the radial artery use:^[1]
  • Patients younger than 75 years old
  • Females
  • Patients with preserved renal function
• There is some limited data regarding the vulnerability to the effect of chronic native competitive flow in composite radial artery grafts.^[25]

• The terms single bypass, double bypass, triple bypass, quadruple bypass and quintuple bypass refer to the number of coronary arteries bypassed in the procedure. In other words, a double bypass means two coronary arteries are bypassed (such as left anterior descending (LAD) coronary artery and right coronary artery (RCA)); a triple bypass means three vessels are bypassed (such as LAD, RCA, and left circumflex artery (LCX)); a quadruple bypass means four vessels are bypassed (such as LAD, RCA, LCX, first diagonal artery of the LAD). Less commonly more than four coronary arteries may be bypassed.
• A greater number of bypasses does not imply a patient is “sicker,” nor does a lesser number imply a patient is “healthier”.^[26]
• A patient with a large amount of coronary artery disease (CAD) may receive fewer bypass grafts owing to the lack of suitable “target” vessels.
• A patient with a single stenosis of the left main coronary artery often requires only two bypasses (to the LAD and the LCX). However, depending upon the anatomy, grafts may also need to be placed to a large diagonal artery, or to additional large obtuse marginal branches.

A coronary artery may be unsuitable for bypass grafting for the following reasons:

• Size: If the native target artery it is small (< 1 mm or < 1.5 mm depending on surgeon preference)
• Location: Some distal locations of the native target artery may not be accessible, or a conduit may not reach far down the native artery.
• Native artery calcification: Heavily calcified native arteries are sometimes technically not amenable to anastomosis of a conduit.
• Diffuse disease: The native artery may not have a section of the vessel that has a minimal disease where a conduit can be grafted to.
• The native artery lies in the heart muscle or is intramyocardial: In this scenario, the native coronary artery is located within the heart muscle rather than on the surface of the heart and a graft cannot be attached to it.

Although the cardiothoracic surgeon reviews the coronary angiogram prior to surgery and identifies the lesions (or “blockages”) in the coronary arteries and will estimate the number of bypass grafts prior to surgery, the final decision is made in the operating room based upon the direct examination of the heart and the suitability of the native target vessel for bypassing.

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