Coronary artery bypass surgery conduits used for bypass


 * Associate Editors-in-Chief:, Mohammed A. Sbeih, M.D. [mailto:msbeih@perfuse.org]

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. 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.

Saphenous vein
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.
 * Saphenous vein anatomy

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 the 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.

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.
 * Saphenous vein harvesting

The endoscopic approach has been associated with lower rates of wound infection, greater patient satisfaction, and earlier mobilization. One small randomized study of 144 patients showed no difference in histologic findings between the traditional and endoscopic techniques. In another small study of 40 patients randomized to the two techniques, no difference was seen in angiographic patency at 3 months. 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. However, non- randomized data from a much larger multicenter study does suggest that endoscopic harvesting may be associated with higher rates of failure and adverse events such as death  and MI.

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

The right internal thoracic artery (RITA)
In multiple arterial revascularizations 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 a 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 is much better than saphenous vein grafts (SVGs) and has less morbidity and mortality rates. 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 right internal thoracic artery (RITA) results in the following in compare with SVG:
 * Less major adverse cardiac and cerebrovascular events.
 * Less perioperative myocardial infarction rates.
 * Less perioperative stroke rates.
 * Less cardiac-related deaths.

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 longer time, it has better long-term results and perioperative outcomes. This has to be proofed and confirmed by more randomized and controlled trials.

==ACCF/AHA Guidelines for choosing Bypass Graft Conduit == {{cquote|

Class I
1. If possible, the left internal mammary artery (LIMA) should be used to bypass the left anterior descending (LAD) artery when bypass of the LAD artery is indicated. (Level of Evidence: B).

Class IIa
1. The right internal mammary artery (IMA) is probably indicated to bypass the LAD artery when the LIMA is unavailable or unsuitable as a bypass conduit. (Level of Evidence: C)

2. When anatomically and clinically suitable, use of a second IMA to graft the left circumflex or right coronary artery (when critically stenosed and perfusing LV myocardium) is reasonable to improve the likelihood of survival and to decrease reintervention. (Level of Evidence: B).

Class IIb
1. Complete arterial revascularization may be reasonable in patients less than or equal to 60 years of age with few or no comorbidities. (Level of Evidence: C)

2. Arterial grafting of the right coronary artery may be reasonable when a critical (>90%) stenosis is present. (Level of Evidence: B).

3. Use of a radial artery graft may be reasonable when grafting left-sided coronary arteries with severe stenoses (>70%) and right-sided arteries with critical stenoses (>90%) that perfuse LV myocardium. (Level of Evidence: B).

Class III: HARM
1. An arterial graft should not be used to bypass the right coronary artery with less than a critical stenosis (<90%). (Level of Evidence: C).}}

Conduit nomenclature
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 (e.g. the left anterior descending (LAD) coronary artery and right coronary artery (RCA)); a triple bypass means three vessels are bypassed (e.g. LAD, RCA, left circumflex artery (LCX)); a quadruple bypass means four vessels are bypassed (e.g. LAD, RCA, LCX, first diagonal artery of the LAD) while quintuple means five. Less commonly more than four coronary arteries may be bypassed.

A greater number of bypasses does not imply a person is "sicker," nor does a lesser number imply a person is "healthier." A person 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 ("narrowing") 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.

Assessment of target vessels for bypass grafting
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 the far down the native artery.
 * Native artery calcification: Heavily calcified native arteries are sometimes technically not amenable to anastamosis of a conduit.
 * Diffuse disease: The native artery may not have a section of vessel that has 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.