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Coronary Artery Bypass Graft
Surgery to improve blood flow to the heart

Coronary artery bypass graft (CABG) surgery is an operation designed to detour blood around a narrowed segment of a heart artery in an effort restore blood flow to the heart muscle. Usually a vein graft from the leg is used for the bypass however other vessels may be used for the graft. The surgery can eliminate chest pain, improve exercise capability and lengthen life.

Anatomy and Physiology

  • The heart is a muscular organ about the size of a clenched fist
  • It lies in the chest beneath the sternum or breastbone. The function of the heart is to supply blood to the body
  • The heart is divided into four chambers, two upper chambers called the right and left atria and two lower chambers called the right and left ventricles (Figures 1A,B,C)
  • The left ventricle of the heart pumps blood through the aortic valve into the aorta, the largest artery of the body, and then through a network of arteries to the whole body
  • The heart valves control the direction of flow of blood through the heart. After passing through the tissues of the body, the blood collects into the veins and returns to the right atrium
  • Blood then passes through the tricuspid valve into the right ventricle. The right ventricle pumps the blood through the pulmonary valve into the arteries of the lungs where the blood picks up oxygen and gives up carbon dioxide
  • The oxygenated blood returns to the left atrium after which it passes through the mitral valve to the left ventricle and the cycle repeats
  • Like all tissues in the body, the, heart requires oxygen filled blood in order to function
  • Blood nourishes the heart through the right and left coronary arteries
    1. The left main coronary artery gives off two major branches, the circumflex and left anterior descending artery (Figure 2)
    2. The right coronary artery gives off the marginal artery before it continues as the posterior descending artery (Figure 3)
      Figure 1a - The heart viewed from in front showing the position of the right and left atria and ventricles. Figure 1b - Diagram of the atria, ventricles and valves of the heart with the heart muscle relaxed (diastole). The yellow arrows show the direction of blood flow through the valves
      Figure 1c - Diagram of the heart during a contraction of the heart muscle (systole). The yellow arrows show the direction of blood flow through the valves
      Figure 2 Angiogram of the left coronary artery. Courtesy K. Patel, MDFigure 3 - Angiogram of the right coronary artery. Courtesy K. Patel, MD

  • Pathology
    • Coronary artery disease (CAD) is a disease of the arteries that surround the heart and supply blood to the heart muscle
    • The coronary arteries become narrowed with the deposition of fatty or calcified material on the inside of the artery. This fatty build up is called atherosclerosis
    • Once atherosclerosis has developed, there may be further narrowing of the coronary arteries by formation of a blood clot
    • When blood flow to the heart muscle is stopped or slowed for 15-30 minutes or longer, there is damage to the heart muscle, which is called a heart attack or a myocardial infarction
    • Whatever the reason for reduced blood flow (fatty build up, blood clot, or spasm) the result is the same, not enough blood and oxygen reaching the heart muscle. Without enough blood and oxygen, the heart muscle begins to fail and subsequently dies

    History and Examination

    • There are risk factors that increase a person's chance of having a heart attack. Major risk factors for coronary artery disease are:
      1. Smoking
      2. High blood pressure (hypertension)
      3. Large amounts of fatty substances in the blood (hypercholesterolemia and hypertriglyceridemia)
      4. Lack of exercise
      5. Diabetes
      6. Positive family history of coronary artery disease
    • Relative risk factors include:
      1. Obesity (more than 20% of ideal body weight), and
      2. Tension or stress
    • Coronary artery disease with reduced blood flow can produce chest discomfort and pain (angina pectoris), a heart attack, congestive heart failure, and even sudden death
      1. Angina, the most common symptom, is a chest discomfort or pain behind the breast bone, typically occurring after exertion, eating a heavy meal, or with extreme emotion
        • Characteristically, the pain subsides within 3-5 minutes after rest
        • The pain may be associated with sweating, nausea, vomiting, and shortness of breath
        • In 25% of the episodes, the symptoms are not typical and pain may radiate to the jaw, teeth, shoulders, and left arm
      2. Progressively worsening congestive heart failure is associated with increasing ankle swelling, shortness of breath, generalized weakness and air hunger.
      3. Sudden death may occur secondary to a massive heart attack or abnormal heart rhythm (arrhythmia)

    Tests

    • Blood tests for special enzymes released by the damaged heart muscle
    • Chest X-ray,
    • Electrocardiogram (EKG)
    • Exercise stress test with or without injection of a radioisotope called thallium
    • If any of the above tests are positive for coronary artery disease, cardiac catheterization (see Cardiac Catheterization) may be performed to demonstrate the site and severity of the coronary artery narrowing
    • Following cardiac catheterization the doctor may recommend coronary artery bypass surgery

    Surgical Procedure

    • A vein graft from the leg (saphenous vein) or an artery from the chest (internal mammary artery) may be used for the bypass. On rare occasions an artery from the forearm (radial artery) or a cadaver vein graft may be used
    • The operation takes approximately three to six hours depending on its complexity
    • The anesthesiology team first inserts intravenous lines and lines for monitoring
    • General anesthesia is administered so the patient will be completely pain free during the procedure
    • An incision along the midline of the chest through the breastbone is used. There usually will be one or more incisions in the legs where the veins are obtained (harvested) for the bypass
    • During the operation a heart-lung machine (cardiopulmonary bypass machine) is used to mix the patient's blood with oxygen and nutrients outside the body and return it to the patient's circulation through tubes going into the aorta
    • The bypass is accomplished by anastomosing a vein graft from the aorta to a point past the occlusion site in the diseased artery
    • An internal mammary artery graft goes directly to a point beyond the occlusion. (Figure 4)
    • In the last few years improvements in technology has allowed the development of minimally invasive direct coronary artery bypass grafting (MIDCAB). This technique involves
      1. Small incisions that avoid splitting the breastbone
      2. Not using cardiopulmonary bypass machine, which means the surgery is done on the beating heart
      3. No clamping or manipulation of the aorta
      4. At this present time the technique is used for grafting the left internal mammary artery, which is a branch of the subclavian artery that goes to the left arm, to the left anterior descending artery of the heart
      5. With advances in technology and the development of drugs that reduce heart activity or even transiently arrest the heart, virtually all coronary artery surgery may be done this way in the future
    Figure 4 - On the left is shown a vein graft from the aorta to a coronary artery. On the right is shown a mammary artery graft to a coronary artery

    Complications

    • More than 420,000 CABG operations are performed each year in the United States. The technological advances in the supportive and monitoring systems have made this procedure safe. The overall risk of complications is about 1-2%
    • Complications include but are not limited to:
      1. Postoperative bleeding
      2. Stroke
      3. Irregular heart rhythm (arrhythmias)
      4. Areas of collapsed lung (atelectasis)
      5. Wound infection
      6. Possible death

    Post Operative Care

    • At the conclusion of surgery, the patient is sent to the intensive care where consciousness is regained
    • Catheters are placed in the arm and neck for administering drugs and fluids, withdrawing blood samples, and monitoring blood pressure
    • There will be one or more tubes in the chest to drain off fluids that accumulate normally during or after the operation
    • A breathing tube connected to a breathing machine (ventilator) goes through the mouth into the windpipe (trachea). The tube is not painful, but it prevents talking
    • The breathing tube is removed when no longer needed for breathing assistance, usually within 24 hours after the operation
    • Deep breathing exercises and coughing are encouraged to help speed recovery. Coughing reduces the chance of pneumonia and fever and will not disturb the incision
    • The average hospital stay is 4-6 days

    After Care

    • The wound is cleansed with mild soap and water. Later, lotion may be used to prevent dryness of the skin
    • It is wise to reduce coronary risk factors as much as possible by reducing dietary intake of salt, cholesterol and saturated fats
    • It is important to maintain an appropriate weight and avoid smoking
    • Weakness is a common feeling on returning home due to lack of use of big muscles. Exercise, such as walking, is a good way to regain muscle strength
    • Sedentary workers may have to wait four to six weeks before returning to work

    see Cardiac Catheterization