and K. M. John Chan
(1)
Department of Cardiothoracic Surgery Hammersmith Hospital, Imperial College Healthcare NHS Trust, London, UK
Introduction
When performing coronary artery bypass grafting (CABG), several decisions need to be made:
1.
The coronary vessel to be grafted.
2.
The choice of conduit (left internal mammary artery, bilateral internal mammary artery, saphenous vein, radial artery).
3.
The site of proximal of anastomosis (aorta, T or Y grafts onto another conduit).
4.
The approach (on cardiopulmonary bypass, off pump)
Currently, most surgeons perform CABG on cardiopulmonary bypass although off-pump CABG is also an established approach.
Coronary Vessel to be Grafted
Coronary vessels should be grafted if they have a stenosis of more than 70% (50% if there is left main stem stenosis) or if they are occluded, provided that there is a distal vessel of reasonable size, generally 1 mm or more in diameter. Grafting vessels with only minor stenoses or very small vessels is to be avoided as early graft occlusion will result.
Choice of Conduit
Traditionally, the left internal mammary artery is grafted to the left anterior descending coronary artery and saphenous veins are grafted to the other coronary arteries. The radial artery is also used, particularly in younger patients with a tight proximal stenosis. Recently, it has been suggested that the use of bilateral internal mammary arteries in young patients may be beneficial.
Harvesting the Left Internal Mammary Artery
The left internal mammary artery (LIMA) is used in almost all cases as it has been shown to have excellent long-term patency and improves survival. The only cases where it is not used is in an emergency situation in an unstable patient where it is necessary to minimise the time of the operation or in very elderly patients.
It can be harvested as a pedicle with the two internal mammary veins on either side of it or skeletonised. We first describe our preferred method of harvesting the IMA as a pedicle.
Pedicle Harvesting of the Internal Mammary Artery
The dissection starts at the distal end of the internal mammary artery (IMA) using diathermy set at 30. The fascia is cut with diathermy about half a centimetre medial to the distal end of the IMA and its vein and parallel to it. The incision is continued for about an inch parallel to the IMA and its vein. Once a plane has been developed, the facia is then pulled downwards and the IMA and its two veins separated from the chest wall by blunt dissection, using the diathermy blade. Any IMA branches are clipped on the artery side and diathermied on the chest-wall side. The distal end of the IMA is then tied off with silk ties and divided, leaving a reasonable length of silk tie attached to the IMA. Gentle traction is applied to the silk tie, pulling the IMA superiorly towards the head. A point diathermy is used, set at 30, cutting the fascia on either side of the IMA and its veins. This frees up the IMA and its veins. The IMA branches are diathermied close to the chest wall. The IMA and its veins are harvested past the first IMA branch until its junction with the subclavian artery. It should lie freely in the chest. The IMA is then placed on a wet swab and papaverine applied to it. Any branches are then clipped. Harvesting of the IMA can usually be completed in about 10–15 min using this technique. It is safe and there is minimal contact with the IMA during harvesting. The important principle using this technique is to get into the right plane where the IMA and its veins are relatively free of the fascia.
Conventional Method to Harvest the Internal Mammary Artery
A more conventional method to harvest the IMA is not to divide it until the end. The initial dissection on the fascia parallel to the IMA and its vein is continued all along its length. The vein and then the IMA are then dissected off the chest wall using blunt dissection with the diathermy blade. Any IMA branches are clipped on the artery side and diathermied on the chest-wall side. A disadvantage with this technique is there is more contact between the diathermy blade and the IMA during the blunt dissection to separate it from the chest wall, thus, increasing the risk of trauma to the IMA. It is also a much slower technique.
Skeletonised Internal Mammary Artery
The IMA can be harvested as a skeleton, i.e. without its two surrounding veins and fascia. An incision is first made with diathermy parallel to the IMA and its vein about an inch along its length and about half a centimetre medial to it. The fascia is then pulled downwards leaving the vein attached to the chest wall, but pulling the IMA off the chest wall. Branches on the IMA are clipped on both the IMA side and the chest-wall side and cut with scissors. The dissection is continued all along the length of the IMA. This method of harvesting the IMA is more challenging and there is increased risk of trauma to the IMA. The advantages of it are an increased length of the IMA and also possibly preservation of the blood supply to the sternum, which may reduce the risk of wound infections in obese diabetics, particularly if the right internal mammary artery is also harvested.
Harvesting the Radial Artery
Before harvesting the radial artery, it is important that an Allen’s test has been performed before surgery to ensure that there is reasonable flow through the ulnar artery. The radial artery is always harvested as a pedicle with its two surrounding veins. The radial artery is very prone to vasospasm and, so, there should be minimal handling of it. The radial artery is held via its two surrounding veins and not directly. Previous attempts at harvesting the radial artery as a skeleton has resulted in early occlusion due to vasospasm.
The radial artery pulse is located proximally and distally. The skin incision is made, starting from the distal radial pulse just proximal to the skin crease at the wrist and then extending proximally, medial to the brachioradialis, ending just before the elbow crease. The fat and then the fascia attaching the brachioradials to the pronator teres and flexor carpi radialis are divided. Once this fascia is divided, the radial artery is easily seen and lies free in areolar tissue. It is then grasped via its vein on either side. Any branches are clipped on the radial artery side and diathermied on the arm side. Depending on the length of the conduit required, the radial artery can be harvested until its junction with the brachial artery, i.e. just before the origin of the ulnar artery with the brachial artery.
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