Radial artery in coronary artery bypass surgery

This section is general in nature.

History
In the early 1970s, a French surgeon Alaine Carpentier used the radial artery as a coronary artery bypass graft. The initial series was published in 1973, but in the discussion regarding another paper one year later it was claimed that there was a high failure rate and this led to widespread abandonment of this technique. In the late 1980s, two patients from this original series which were known to have failed radial artery grafts, presented without symptoms of coronary ischaemia. They underwent coronary angiography and these radial arteries were found to be patent and normal. A series of 104 patients was then published in 1992 by another French surgeon Christophe Acar with the first 50 of these patients undergoing coronary angiography revealing 100% patency of the radial artery in the early time frame. This led to a worldwide revival in the use of this conduit.

Surgeons in Melbourne, including Royal Melbourne hospital were at the forefront of this revival using the radial artery. A few surgeons harvested and use this conduit selectively in 1994 and 1995 with very good clinical results and this led to a very dramatic uptake in the use of this conduit by other surgeons at hospitals affiliated with the University of Melbourne. In the paper published in 1999, radial artery use increased from less than 20% in the first half of 1996, to more than 80% in the second half of 1996. For the past decade therefore, most patients at Royal Melbourne hospital have received at least one radial artery graft.

Harvest technique
The original technique developed at Royal Melbourne hospital remains almost entirely unchanged. Download the PowerPoint presentation or view the video is of this harvest technique. This technique was described in a paper from 1999. The radial artery is exposed and metal clips are used to secure the side branches and electrocautery (diathermy) is used to divide these branches. It is important to enter the neurovascular plane. Topical and intraluminal papaverine (vasodilator) is used. The forearm is closed without apposition of the deep fascia. Our results have demonstrated an extremely low incidence of clinically relevant hand ischaemia and a low incidence of sensation changes for wounded tenderness. Subsequent studies have examined the maximum blood flow to the forearm some years postoperative demonstrating preservation of good blood flow to the forearm. See current research projects relating to the radial artery.

Principles for use of radial artery
The principal rationale for using the radial artery is to provide more arterial coronary artery bypass grafts. The rationale is that arterial grafts will behave in a relatively similar manner and quite differently from vein graft. Vein grafts are subject to progressive and accelerated atherosclerosis such that approximately 50% of vein grafts will have already become occluded at about 10 years postoperative.

The second principle in the use of radial artery was to try and use it in a more efficient manner. What this means, is that the radial artery or arterial grafts in general, be used for more than one distal anastomosis per conduit (sequential grafting). In this way, a greater number of bypass "grafts" can be performed with fewer numbers of conduit. The underlying assumption is that the arterial grafts proximal to these anastomoses will remain patent.

This is a crucial point, because it had become established cardiac surgery practice that each distal anastomosis should have its own conduit. Probably the reason for this arose from the early experience of coronary artery bypass surgery in the late 1960s and the early 1970s. At this time, it was quite common for a single vein graft to be used originating from the aorta and then being passed around the heart with sequential grafting methods to various distal anastomosis targets. However, the most common site for vein grafts to fail was in the proximal segment, near to the aortic anastomosis. When this happened, all of the dependent grafts were lost resulting in severe ischaemia or death. Therefore, it became established practice that each distal anastomosis should receive a separate vein graft, so that if it did fail then only one anastomosis was lost.

The third principle of radial artery use was to achieve a shorter distance between the origin inflow to the conduit and the first sequential anastomosis, thereby further increasing the efficiency of conduit used. This led to a relatively common method of composite arterial graft construction (Y graft). Simply, this means that the radial artery is sutured to the left internal mammary artery along its length. This join was variably referred to as a Y graft, a T graft or a composite graft. The first anastomosis along the length of the radial artery could therefore be quite close to the origin of this conduit. Secondly, it was found that the radial artery using this method of reconstruction, was always of sufficient length to graft the circumflex and right coronary arteries, whilst the left internal mammary artery was sufficient to graft the left anterior descending artery territory. Therefore, with these two conduits or three coronary territories could be routinely grafted.

The fourth principle of radial artery harvest grafting is to achieve total arterial revascularisation. This situation arises when 100% of coronary targets are supplied by arterial conduits. Use of the radial artery, sequential grafting and composite Y gafting allow for a very high proportion of patients receiving arterial grafts exclusively. The underlying assumption is that this will translate into longer term patency of conduits and therefore surgery will be a more durable treatment. There is some evidence of this in the literature; as well as some evidence that it leads to better short term (in hospital) survival after this form of surgery.

Late effects of radial artery harvest on the forearm our research found that there was no reduction in strength after harvest as well as no reduction in flow to the forearm.
See the research section for further information
Abstract and Paper

Also we have scanned the remaining ulnar artery 7-11 years following radial artery harvest and have found no evidence of increase atheroma as a consequence of removing the radial artery. This is very new and confirms the ongoing use of the radial artery as a conduit for coronary artery bypass surgery.
??? See the research section for further information
Abstract and Paper
See the Presentation ??? Video (iPod version) or PowerPoint

Y graft construction
What is a Y graft? Simply, this is a join between two coronary artery bypass conduits. Usually this will be the left internal mammary artery and the radial artery, but alternatively it may be the right internal mammary artery as a free graft joined to the pedicled left internal mammary artery. Far less commonly, it may be both radial arteries joined together with one of them attached to the aorta for inflow. The joined is made at an angle so that the branch appears reminiscent of the letter "Y".

The purpose of the Y graft is to conserve conduits so that more coronary artery bypass grafts can be performed with fewer conduits. This produces the morbidity associated with harvesting more arterial grafts such as the internal mammary artery or the radial artery or vein grafts. It also increases the proportion of grafts that are arterial rather than venous.

The principal of positioning of the Y anastomosis is to place it at that point where the left internal mammary artery passes through a hole in the pericardium at the border of the heart. In this way, no additional length of the radial artery or second conduit is wasted. The internal mammary artery will then graft everything anterior to this point and the second conduit, usually the radial artery, will graft everything posterior and inferior to this point. Therefore, the second conduit was used to graft the circumflex and right coronary territories.

Interestingly, the distance between the subclavian artery and the border of the heart is easily found by placing the left internal mammary artery over the proximal aortic arch and distal ascending aorta. This is where the anastomosis can be constructed in a very convenient situation. Also, this length would be the same as if the left internal mammary artery were taken proximally and internal mammary artery was divided proximally and used as a free graft and attached to the proximal ascending aorta. Similarly, one radial artery may be attached to the ascending aorta and grafted to the left anterior descending and diagonal arteries and the second radial artery may be attached to the first radial artery as a Y graft approximately one third along its length and then used to graft the circumflex and right coronary territories in exactly the same way as using the pedicled left internal mammary artery. In general, the left radial artery is 10 - 20% longer than the free internal mammary artery graft.

The Y graft anastomosis is normally performed before any aortic cannulation or cardiopulmonary bypass. This is because the anastomosis is constructed in the same situation as one would normally cannulate the aorta, and it is simpler to perform this anastomosis before the cannula is placed. The internal mammary artery is opened on the chest wall surface. The radial artery is prepared in the usual manner. The most common suture technique is to place the first suture through the proximal end of the left internal mammary artery incision. The second needle is then passed through the apex of the radial artery graft from within the lumen. This suture is then continued from outside of the left internal mammary artery through the radial artery until a point is reached just beyond the distal end of the incision of the left internal mammary artery. Then the original first needle is used to sew the other side of the anastomosis. This is the "forehand" technique.

Alternatively the distal end of the left internal mammary artery incision maybe used first or the "backhand" suture method may be used.

At the end of constructing this anastomosis, the microvascular clamp on the left internal mammary artery is removed and intraluminal papaverine is injected via the radial artery conduit. This is then temporarily occluded with a small vascular clamp. One of the adjacent veins of the radial artery is then sutured to the pedicle or edge of the left internal mammary artery to maintain its position and try and protect the Y graft anastomosis from any inadvertent traction injury.

Normally medium metal clips are placed on one aspect of the radial artery so that it is easy to identify any twisting of the conduit. Usually the superficial surface of the radial artery is placed on the aspect of the heart because normally there are no veins the cross on this side of the radial artery and therefore no additional work to divide these veins is required during sequential grafting.