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Surgery for ischaemic heart disease

CORONARY ARTERY BYPASS GRAFTING

Usually abbreviated to CABG, this is the definitive surgical treatment for ischaemic heart disease (IHD). The concept is simple: you have a blockage or narrowing in a coronary artery, and it is important that blood gets to the area of the heart on the far side of the blockage.
You therefore need to divert the blood flow past the blockage. This can be done by connecting a new tube or conduit to the blood supply on the normal side of the blockage, and connecting the other end to the coronary artery beyond the blockage.
The CABG operation will allow blood to ‘bypass’ the blockages or narrowings in your coronary arteries. The number of bypasses you have depends upon the number of arteries that are blocked, and the operation is basically the same for each blockage.
So, when people talk about a ‘triple bypass’ it means that three arteries are blocked, but it is quite common to have a single, double, quadruple or even more bypasses in your operation. The number is not especially important, as long as all arteries with significant narrowing or blockages get bypassed.
In this way a normal blood supply is re-established to all the deprived areas of heart. It is a bit like plumbing, really.

There are several ways of doing this, but they all follow the same broad principles:
• Most operations are performed with the aid of cardiopulmonary bypass (CPB), so that the heart can be stopped to make the surgery easier. There are, how­ever, well-established techniques and equipment to allow CABG to be performed without CPB. There has been extensive development of specialised equipment for stabilisation of the parts of the beating heart to be operated upon, and to keep the operative field clear of blood. This ‘off-pump’ surgery is becoming more and more popular and has the advantage of avoiding the complications associated with being on the CPB machine. However, these complications are rare anyway, so it is still up to the preference of the individual surgeon as to which technique he or she will use. In general, ‘off-pump’ surgery is reserved for cases requiring fewer numbers of bypass grafts, although some surgeons will happily use it for almost all cases.

• Myocardial protection is needed (see page 41), and the surgeon chooses which method he or she prefers.

• A conduit is needed to connect the vessel before the blockage with the vessel beyond.

Conduits
There are a number of different conduits that can be used, and they are broadly divided into vein, artery and synthetic.
Veins or arteries from your own body are by far the best things to use, because there is no danger of rejection or infection. Not long ago, vein was used in nearly all surgery for CABG, but nowadays arteries are playing a much more dominant role. They are thought by many to be a far superior conduit to vein and there are some surgeons who use only arterial grafts. There is still no conclusive evidence for this, how­ever, and both are excellent options. In fact, the recent innovation in the development of statins, the drugs that keep cholesterol low, is very likely to be a factor in keeping vein grafts open for longer and longer.

• Vein:

In over 90 per cent of all CABG operations performed, the patient’s leg is opened to take out some vein. This is usually the long saphenous vein, a superficial vein on the inside of your leg that runs from your ankle to your groin. This vein is not important to you, and you do not suffer any ill-effects from its removal. It is, in fact, the vein that becomes unsightly when you have ‘varicose veins’ and is often removed anyway. The amount that is taken out depends on the number of bypasses you need, approxi­mately eight inches being required for each. Other veins from the arm are sometimes used, but only if it is not possible to use the long saphenous vein (for example, if it has been removed for varicose veins, or it is too small). You must be aware, however, that when you wake up, you may have scars on either or both legs, and maybe even your arm, because if the surgeons cannot find any usable vein at first they will move on to the next best place.

• Artery:

The advantage of using arteries is that blood is already being actively pumped down them. If you can find a relatively unimportant one near the heart, it is only necessary to connect the one end to the coronary artery beyond its blockage, and you have provided a new blood supply to the region. The internal mammary arteries (IMA) are ideally suited for this, and have had a revolutionary effect on CABG surgery. They are located behind the breastbone (sternum), and there are two of them: a left (LIMA) and a right (RIMA). They help in supplying blood to the breastbone, but because this bone has other sources of blood, one or both of them can be disconnected from it.

The LIMA is used in more than 90 per cent of CABG operations. For a ‘triple bypass’, the most popular choice of surgeons is either the LIMA and two lengths of long saphenous vein (LSV), or the LIMA, the radial artery and one length of LSV.

Use of the RIMA is becoming increasingly popular, and some surgeons use it as well as the LIMA for nearly all cases. After the chest has been opened, the surgeon carefully teases away the IMA from the back of the breast-bone, leaving one end connected to the big artery coming from the aorta, and disconnecting the other end from the bone. When disconnected, blood will squirt from the end indicating that it is good enough to use. A temporary clip can be put across the end to prevent it bleeding, and the IMA is now ready to be connected to the coronary artery.
As we have mentioned earlier, arteries are thought by many to be better conduits, although there is no substantive proof and there are many trials under way at present in an attempt to prove the benefit. There are some surgeons who are very much in favour of ‘total arterial revascularisation’ (TAR). This means using arterial conduits, and not veins, for all of the bypasses. This can be done by using both IMAs, combined with either the gastro­epiploic artery from the stomach, or the radial artery from the wrist. The gastroepiploic artery is useful because, like the IMA, it lies close to the heart, and only one end needs to be disconnected. The disadvantage is that it is in your abdomen, which means a longer operation. The radial artery is in your wrist, and is obviously too far from your heart to be used similarly. In this case it is taken out completely, and used as a ‘free graft’ where each end is connected to either side of the coronary artery blockage, in much the same way as vein.

• Synthetic grafts:

These are really a last resort, and are very, very rarely used. They last for a much shorter period of time than any of the other conduits, and are only used if no usable vein or artery can be found in your body. They are usually made of Dacron or Teflon and, although well sterilised, pose a much greater risk of becoming infected, as do any other foreign materials being implanted into your body.

How the operation is done

Your chest is opened down the middle from the ‘notch’ between your collarbones to the ‘V’ of your ribcage. Your breastbone is also cut neatly down the middle using a special saw. Once this has been done, it is possible to open your chest cavity surprisingly wide, to get a very good view of the heart. One or both IMAs are then taken down.

While this is going on in the chest, a second surgeon is usually taking the vein out of the leg, and if needed a third surgeon can take the radial artery out of the arm (usually the left). When the surgeon at the chest has taken the IMA, the next stage is to put the cardiopulmonary bypass pipes into the aorta and right atrium (see ‘Cardiopulmonary bypass’) and connect them to the heart–lung machine. When the surgeon is happy that there is enough conduit, he or she can tell the perfusionist to start the heart–lung machine, and the patient is then ‘on bypass’ and the CABG can be performed.
The precise order of events depends on the method of myo­cardial protection used, but the end result is the same. The conduit (vein or artery) is sewn on to the coronary artery beyond the blockage using a very fine stitch, for which the sur­geon often uses special magnifying spectacles called loupes. The other end of the conduit is sewn on to the aorta, to a small hole that has been cut in it. In this way, blood pumped up the aorta will pass down the new vein graft to the area of heart beyond the blockage.

An important point to note is that the vein must be sewn in upside-down, because it contains valves and only allows blood to flow in one direction. The free end of the IMA or other arterial grafts is sewn to the coronary artery in a similar way to that described for the vein. The stitches are close enough together to prevent leakage, and after a period of time the join heals just like stitches in your skin.

When the grafts have all been sewn on, it is time to come ‘off bypass’. As the operation is performed at a lower temperature for myocardial protection, the perfusionist is asked to warm the patient up before this can happen. After the patient is off bypass, the pipes can be removed, and the chest closed. The breastbone is put together using six to eight stainless steel wires, before the other tissues and skin are sewn up. These wires hold the breastbone together tightly and, within about three to six months, the bone will have healed up itself. The wires, however, remain in place long term. After your oper­ation you will be taken to the ICU.
CABG generally lasts a good period of time, usually in excess of 10 years and often a lot longer. Factors that will keep the bypass grafts ‘open’ and healthy include good control of diabetes, cholest­erol and blood pressure and non­smoking. Failure to control any of these may result in much earlier ‘furring up’ and blockage of the grafts, with the consequence of heart attack or the need for a repeat operation. If the grafts do not last, your symptoms may start to reappear. This results from the unavoidable fact that the disease process that ‘furred’ your coronary arteries up in the first place does not go away, and is doing the same to your new conduits. When this happens, you may need to have the operation again, and this is known as a ‘re-do’. It is similar to the first operation, but technically much more difficult, because the anatomy has been distorted. Finding suitable conduit can be quite tricky too. This is because the best conduit (LIMA and veins) has usually been taken out for the first operation. For all these reasons, your operative risk is proportionally higher.

OTHER SURGICAL PROCEDURES

There are a few other surgical procedures that are performed for IHD, but they are much less common than CABG.

• Aneurysmectomy:

This means the cutting out and repair of an ‘aneurysm’ which is a swelling in a dead area of heart muscle caused by a heart attack. If an aneurysm exists, it needs to be inspected carefully during the operation, because if it is thin, it is in danger of rupturing and needs to be repaired. This is a relatively quick and easy procedure.

• A ventricular septal defect (VSD) repair:

This can be a life-threatening problem and usually means that the person must have emergency surgery. It is a hole that forms in the dividing wall (septum) between the left and right ventricles. The hole is a rupture in a dead piece of muscle, caused by a heart attack. It is relatively rare, but if it does occur, the patient is extremely unwell and the risks are very high.

• Transmyocardial revascular ­isation (TMR):

This is an experimental technique that was developed several years ago and initially held a lot of promise. It was thought to be an option for the treatment of patients with severe IHD, but who were not suitable for conventional CABG as a result of very small coronary arteries. It involves the use of a laser to drill about 30 holes in the ventricles of the heart. This is supposed to stimulate the formation of new blood vessels in the substance of the muscle, and therefore relieve the ischaemia. Unfortunately, results have not lived up to expectations and the tech­nique has been largely abandoned. It is still under scrutiny, however, and only appropriate for a small proportion of patients at present, usually those with poor ventricular function and small coronary arteries.
There are very limited positive research data on this technique to date, and it is regarded with a great degree of scepticism by many. For this reason, it has largely been abandoned by most surgeons.