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Coronary Surgery Coronary arteries are the blood vessels that supply the heart with blood. They arise from the main blood vessel called the aorta and lie on the surface of the heart. There are normally three main branches and so this is why some times severe disease is referred to as triple vessel disease. The disease There are two main consequences of having atherosclerosis of the coronary arteries. The first is that it may narrow the coronary arteries and reduce the flow along the length of the artery. This will not necessarily stop blood flowing in the artery, but may limit the amount of flow. This can explain why some times people will get chest pain and shortness of breath. The amount of blood flowing when they are at rest, for examples sitting in a chair, may be sufficient. But when they exercise, all of the other muscles such as leg muscles and back muscles need more blood in order to do the work of exercise. The heart is just a muscle and if it is needed to pump more blood, it is doing more work and therefore needs more blood itself to do this exercise. The narrowings in the coronary arteries limit the amount of additional blood flow that flows. This is easy to understand. In the bathroom sink, open the tap fully. Water will be seen to be gushing out rapidly from the. Try then closing the tap and no noticeable difference to the water flow will occur until at least 60 or 70% closed when there will be an obvious reduction in the flow of the water. Therefore, symptoms do not generally occur at rest until the coronary arteries are at least 70% narrowed. However when additional amounts of blood are needed to flow along these coronary arteries (like when exercise is performed), then narrowings of less than 70% will become important because they prevent a necessary increase in the flow of blood along the coronary artery. The symptoms that narrowed coronary arteries may cause include chest pain and shortness of breath. Chest pain occurs because when more blood is needed by the heart muscle than is being delivered by the coronary arteries, the heart muscle tries to make energy which does not require oxygen. This process is much less efficient and lactic acid is produced. The nerves in the heart detect this lactic acid and the patient will feel pain. The reason that chest pain is felt in an unusual way or alternatively back pain or throat pain or left arm pain, relates to the type of nerves that supply the heart with feeling. They are referred to as autonomic nerves, and the brain tries to place the pain that is experienced by these nerves onto the surface of the body. These nerves are similar to the origin of the nerves of the lower neck and upper chest as well as the arms. This is why heart pain generally is felt in this area and is called referred pain. However, this type of pain is not specific to the heart, because the same autonomic nerves will supply other local organs like the oesophagus and the lungs. Therefore heartburn which is pain arising from the oesophagus can sometimes be indistinguishable from pain arising from the heart. This is why the nature of the pain is not diagnostic of heart pain necessarily. The second main change that can occur with coronary arteries is that they may become blocked. Reasonably commonly, one of the plaques which contains cholesterol and other material in the wall of the coronary artery may rupture its surface. The contents of this plaque will then enter the bloodstream of the coronary artery and cause the blood to clot. This process only takes a few seconds, and effectively blocks the artery. Therefore the part of the heart muscle that is being supplied by this artery suddenly loses its blood supply and will die. This is called a heart attack. The size and the importance of the heart attack relates to the position within the artery where this blockage occurred. So a large heart attack may be caused by blocking the origin of a large coronary artery or coronary artery sub branch. A small heart attack may occur where a small coronary artery sub branch is blocked. In other words the amount of the heart muscle that is being affected his quite variable. Usually this damage is permanent and during the healing phase (assuming the patient survives), the dead heart muscle will be replaced by a scar. There are two interesting possibilities that sometimes arise. The first is that it is possible for a coronary artery to block without having a heart attack. This is more by luck than related to anything the patient may do to prevent a heart attack. We believe that if the blockage occurs very slowly, then over time alternative channels will open up allowing for blood flow to occur around an area of severe narrowing in a coronary artery. Therefore when it blocks off completely, there is still sufficient blood reaching the heart muscle beyond the blockage to keep it alive. However these tiny channels will not be sufficient to provide a significant increase in blood flow when the patient wants to exercise and so a patient may still have symptoms when they exercise although they did not suffer a heart attack when the coronary artery blocked off. The other relatively uncommon thing that may occur is for a heart attack to occur without pain. This can easily occur when the nerves to the heart are not working properly. In some people the nerves did not work very well because of diseases that can affect the nerves, most commonly diabetes. Alternatively, sometimes the nerves appear not to work very well without an obvious explanation. However, it is important to understand that even if there is very little pain, having a heart attack is still a very important thing. An analogy is useful. If you had the nerves to your hand cut so that you had no feeling in your hands at all, and placed your hands in a pot of boiling water, you would not feel any pain. Yet we know that your hand would be severely burned by the boiling water. This is the same for the heart, because if the nerves are not working very well, you can still have a heart attack without feeling any pain or a great deal of pain. Treatments Coronary intervention. This involves passing a wire through a narrowing or blockage in coronary artery and dilating that narrowing or blockage using a small fluid filled balloon. This will crush the artery at this point. Usually these days a metal stent will be placed in this area as well. The area will remain at risk for developing a clot and also narrowing during the healing process. A variety of drugs are usually administered to try and lower this risk. This approach is dealing with a plumbing problem by trying to reduce a local narrowing in the artery. It does not alter the disease process that made the artery narrow in the first place. Coronary artery bypass surgery. This approach attempts to deal with the same plumbing problem by sewing on an alternative artery beyond the point of narrowing or blockage so that there is an alternative and supplementary route for blood flow to occur. The most commonly used tubes for this purpose include an artery from the chest wall (internal mammary artery), an artery from the forearm (radial artery) or less commonly these days, vein taken from the leg. Again, this form of treatment does not change the underlying disease process that made the coronary arteries narrow in the first place. Who makes the decision to perform surgery? What tubes (conduits) will be used? We currently believe that arterial bypass grafts (arteries from elsewhere in the body) will provide the best long-term durability for coronary artery bypass surgery. This is based on substantial knowledge in relation to the artery from the chest wall (internal mammary artery) and more limited evidence for the artery from the forearm (radial artery). We also have substantial knowledge about the fate of vein grafts from the leg. These fail in a relatively predictable manner, and generally speaking approximately 50% of vein grafts will have blocked by 10 years following surgery and more than 85% will have blocked by about 15 years. Therefore, our preference is generally to try and avoid vein grafts. We also have a preference for using arterial bypass grafts in a more efficient manner by using one tube to graft more than one coronary artery target when required. In this way we can try and minimise the number of conduits that we need to harvest, and therefore reduce the risks associated with harvesting the conduits. How does the surgeon quote the risk of surgery? The normal risk for coronary artery bypass surgery in our practice in Melbourne would tend to reflect the lower end of the complication risk quoted. Typically the risk of a major complication, such as a stroke, a serious wound infection, a heart attack, serious pneumonia etc, or alternatively a series of complications leading to the death of the patient, would be about 3-4%. By considering the complexity of the surgery itself, but usually more importantly by considering other medical problems that the patient may have including advanced age, this risk may be higher than normal. Typically we would consider moderate risk to be in the 5-10% range, high risk being 10-30% and prohibitive risk being more than 30%, for elective surgery. There are certain non coronary artery bypass surgery procedures which are sometimes undertaken with higher risk than 30%, for example, acute aortic dissection. Here, the survival without surgery approaches 0% and with surgery may be 50% or more. This represents a different category to that generally discussed in relation to coronary artery bypass surgery. Also, coronary artery bypass surgery may simply be a part of the operation which may also involved a valve replacement etc. The way these figures are arrived at is not precisely determined because there is a wide variation in the institutional practice, timeframe, surgeon capability and patient factors. Nevertheless an approximate incidence of the following complications may apply in our practice:- Approximate rate of serious complications Some patients will state that they would rather die on the operating table whilst undergoing very high risk surgery, rather than accepting that surgery is not warranted because of the risk of surgery. From the patients perspective, this may well be sound logic and reasonable. However, it may not be reasonable for the surgeon who then becomes an executioner rather than a helper; the family who may be subjected to protracted deterioration of the patient in hospital; or the hospital system or society that may invest vast resources attempting to treat someone with little prospect of a favouable outcome whereas these resources could be used to successfully treat several lower risk patients. The surgeon needs to feel that they and the team are more likely to do good than harm - (first do no harm). Less severe complications significantly more common, and generally are seen as more of a nuisance value than having serious long-term consequences. That is not to say that they do not cause significant distress at the time. Rapid heart rates which are transient in nature (atrial fibrillation) are very common and are present in approximately 30-40% of patients. Also being a big chest operation and involving a fairly long anaesthetic, lung related changes are also common such as partial collapse of the lower parts of the lung, some early chest infection or fluid in the lower part of the chest. These may represent approximately 25% of patients. Pain is an inevitable part of major incisions for surgery. In our individual practice, we offer high thoracic epidural as a form of pain relief for the first two days which proves to be a highly effective form of pain relief. However some patients are not suitable for this technique, and in the practice of most other surgeons this option is not offered. Alternatives include intravenous morphine like drugs. Typically pain following surgery is manageable by tablets alone 48 hours after surgery. Timeframes of recovery Full and complete recovery following coronary artery bypass surgery will typically take about six weeks. There is a very wide variation between patients however. During this time there will be a progressive improvement. One of the slowest part of the wounds to heal, is the breast bone (sternum). All bones heal fairly slowly, and the sternum is divided in order to perform the surgery. This represents the equivalent of a fracture of the arm or leg. An internal splint to this bone is used (sternal wires). These wires are left in permanently unless there is some difficulty with them when they can be removed fairly easily after the bone has healed. It will normally take about six weeks for bone to heal sufficiently for general use. Therefore during this time we would normally suggest that patients do not lift up heavy objects or exercise their arm and chest vigorously whereby the bone edges may move and healing has to recommence. |