Coronary Artery Bypass Surgery
Often simply called bypass surgery, this operation is extremely effective in relieving symptoms of coronary artery disease (CAD) and angina. It can relieve chest pain, reduce fatigue and dependence on medication, increase the ability to exercise, and greatly enhance well-being. For some people, the procedure is literally a lifesaver.
Bypass surgery is a fairly low-risk procedure. For someone who has an otherwise normal functioning heart, no history of heart attacks, and no conditions that could make surgery dangerous (such as chronic obstructive pulmonary disease), non-emergency bypass surgery carries a risk of death of 3% or less.
There is a 5% chance of a heart attack during surgery. The risk from surgery is a bit higher if someone has had a heart attack before, or has other cardiovascular problems. About 90% of people who undergo the surgery experience complete or dramatic relief of their symptoms.
Coronary artery bypass surgery is performed on people who suffer from severe CAD, a condition involving the clogging of arteries that bring blood to the heart muscle caused by fatty deposits on the inner walls of the arteries. The surgery is also performed on people who suffer from severe angina (pain that occurs when the heart muscle isn’t receiving enough oxygen). Angina is usually caused by CAD, which is the major cause of heart disease in North America.
The coronary arteries lie on the heart’s surface. They bring oxygen-rich blood to the heart muscle (myocardium). For the heart to pump blood normally, the heart muscle needs a constant supply of oxygen-rich blood from the coronary arteries. When coronary arteries become blocked, the oxygen supply to the heart is reduced.
There are two general patterns of blockage. In the first pattern, blockage develops slowly and only partially blocks the artery. This usually results in chest pain or angina because the heart is not getting enough oxygen. The second pattern is a complete blockage that usually develops quickly. With a complete blockage, parts of the heart muscle are not getting oxygen and heart muscle cells begin to die. This is called a myocardial infarction, or heart attack.
The most common cause of a partial blockage is cholesterol and fat deposits on the inner walls of the coronary arteries. The gradual buildup of these substances may form fatty deposits called plaques in a process known as atherosclerosis (hardening of the arteries). The plaques bulge into the large branches of the two main coronary arteries and restrict the ability of blood to flow through them. Eventually an artery can become blocked or occluded, and no blood can flow through it. Plaque can also help to form blood clots (thrombosis). The slow buildup of a blood clot can narrow the affected artery even more, while a quickly developing clot can abruptly close off the artery.
Symptoms and Complications
The key symptom of CAD is heaviness or pressure in the chest, but it may also be felt in the arms, jaw, throat, or upper back. Symptoms usually occur when you exert yourself and will go away with rest. However, not everyone with coronary artery disease experiences warning signs. In fact, some people will only notice significant fatigue or tiredness with exercise. The main complications of CAD are angina and heart attack.
Making the Diagnosis
A doctor will diagnose coronary artery disease (CAD) on the basis of symptoms and tests. Your doctor will perform a physical examination and blood tests to help with the diagnosis. Your doctor will recommend tests such as an exercise stress test, a cardiac nuclear scan, and cardiac catheterization. Catheterization indicates the severity of the disease and shows which arteries are affected. This test plays an important part in deciding if someone is suitable for bypass surgery.
Treatment and Prevention
Coronary artery bypass surgery is an open-heart procedure. The person is placed under general anesthetic. The surgeon will begin the operation by making an incision down the centre of the chest, then dividing and separating the breastbone (sternum). Tubes are then attached to the heart and connected to a heart-lung machine that keeps the blood supplied with oxygen. Blood will be pumped from the heart to the machine and back to the body to be circulated again. Blood pressure, temperature, and breathing will all be regulated. It is sometimes possible to avoid cutting the breastbone by making smaller incisions in the chest.
Once the heart-lung machine has taken over for the heart, the surgeon will clamp the aorta (a major artery taking blood from the heart to the rest of the body). He or she will then graft or sew a vein or artery taken from another part of the body onto the blocked coronary artery. The grafted veins or arteries join the aorta to the coronary artery, bypassing the blocked part of the coronary artery to bring oxygen-rich blood to the heart. The vein used for the graft is usually taken from the leg (the saphenous vein).
Surgeons will often use at least one artery as a graft. This is often an internal mammary artery taken from the left or right side of the chest wall beneath the breastbone. The mammary artery is sewn directly on to the blocked coronary artery. In some cases, the mammary artery from the other side of the chest or an artery from the forearm may also be used. Both the veins and arteries used are non-essential in their original location, and their removal is not harmful.
Once the grafting is finished, the person is taken off the heart-lung machine. The heart and lungs will take over again, and the surgeon will rejoin the breastbone with stainless steel wires. As few as one and as many as 5 or 6 bypasses may be performed in a single operation.
New techniques of bypass surgery may be used in some cases. The most common method is the "beating-heart" technique. This does not use the heart-lung machine setup but still needs to be done through the incision in the middle of the chest. Bypasses are sewn directly onto the heart without stopping the heart. This reduces the risk of the complications from the heart-lung machine.
An average operation lasts from 3 to 6 hours. Patients are then monitored in an intensive care unit for at least 24 hours and may be kept sedated for their comfort. Most patients can eat solid foods after a day or two and leave the hospital in about 5 to 7 days. The stitches are removed about a week after the operation. The doctor will often recommend an exercise program to help the healing process and to ease the return to previous levels of activity and return to work.
After surgery, all patients will need to continue taking medications that decrease the work of the heart and reduce the risk of future heart attacks. The medications usually prescribed are acetylsalicylic acid (ASA)* to prevent blood clots, beta-blockers, cholesterol-lowering medications such as the statins, and ACE inhibitors (medications that control blood pressure). Artery grafts rarely go on to develop CAD. Approximately 90% still work 10 years after the surgery. Vein grafts more often become obstructed. After 10 years, about 50% of vein grafts become narrowed or clogged.
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