Cardiac bypass

Definition

Cardiac bypass surgery, also called a coronary artery bypass graft (CABG), is a procedure in which a vein or artery from another part of the body is removed and sewn (grafted) into one of the coronary arteries in order to allow blood to flow around (bypass) a blockage in the coronary artery. The first cardiac bypass surgery was performed in 1967 at the Cleveland Clinic. In 2008, about 375,000 CABG surgeries were being performed every year in the United States.

Purpose

Cardiac bypass surgery is done to improve the quality of life and ideally extend the life of an individual who has a severe deficiency in blood flow through the coronary arteries. The coronary arteries supply blood to the heart. Insufficient blood flow is caused by plaque build-up and hardening of the

arteries (atherosclerosis ) and can develop in any artery. When atherosclerosis occurs in the coronary arteries, it is called coronary artery disease (CAD). CAD substantially increases the risk of heart attack (myocardial infarction). Cardiac bypass surgery does not cure atherosclerosis; it simply establishes a new pathway for blood flow to the heart.

To understand how cardiac bypass surgery works, it is helpful to know something about the anatomy of the heart. The heart is a muscle containing four compartments or chambers that separate oxygen-poor blood from oxygen-rich blood. The atria are the top chambers. They receive blood from the body. The ventricles are the bottom chambers. They pump blood out to the body. Oxygen-poor blood enters the right atrium, then moves through a valve to the right ventricle. It is then pumped out of the right ventricle to the lungs where it picks up oxygen. The oxygen-rich blood returns to the left atrium of the through the pulmonary vein, flows through a valve to the left ventricle, and is then pumped into the aorta. The aorta is the only artery carrying blood out of the heart. Smaller arteries branch off and carry blood to the rest of the body from this very large, thick, long artery. The first arteries to branch off the aorta are the coronary arteries. These carry a continuous supply of oxygen-rich blood to the heart. Blockages in these arteries can cause heart attack and death .

When the coronary arteries are 70% or more blocked, the danger of heart attack greatly increases. In some patients, the coronary arteries can be opened using a minimally invasive procedure called balloon angioplasty . Balloon angioplasty is done by threading a catheter with an expandable tip expanded into the circulatory system. When the catheter reaches the site of the blockage, the tip is expanded to force the artery open. Astent is then placed in the artery to keep it open. Balloon angioplasty is not always successful and is not always the procedure of choice for treating CAD.

In general, CABG is done:

• when balloon angioplasty has failed
• when the patient has chest pain (angina) that cannot be controlled by lifestyle changes or medication (about 40% of patients with angina fall into this category)
• when the left main coronary artery is blocked before it divides into two smaller coronary arteries
• if the patient has diabetes and angina and two or three coronary arteries are blocked
• if any three coronary arteries are blocked and the patient's heart has begun to weaken

Precautions

Although the risks associated with cardiac bypass surgery increase with the age of the patient, age is not an absolute barrier to having this surgery; an otherwise healthy eighty year old can have successful cardiac bypass surgery. Nevertheless, people who have a severely weakened left ventricle and an ejection fraction of less than 30% are poor candidates for this operation. The ejection fraction is the percentage of blood pumped out of the left ventricle with each heartbeat. A normal ejection fraction is about 75%.

Description

On the day of the surgery, the patient is given a sedative before going into the operating room. Once there, the patient receives intravenous anesthesia. The operation generally takes three to five hours.

The most common CABG procedure is an open-heart procedure. The surgeon makes a 6–8 inch (10–15 cm) incision in the chest and then breaks the breastbone (sternum) to gain access to the heart. During the operation, the heart must be still (not beating), so the patient is put on a cardiopulmonary bypass or heart-lung machine. This machine keeps oxygen-rich blood flowing through the body while the heart is not pumping.

The surgeon next removes the vein or artery that will be used for the bypass graft. The preferred vessel is the internal mammary artery (also called the internal thoracic artery) in the chest. Alternately, the radial artery in the forearm may be used, and if necessary, the saphenous vein from the leg. Arteries are preferred for the graft because they are less likely than veins to become blocked over a ten-year period. Often, more than one coronary artery is blocked, so multiple bypass grafts may be needed.

One end of the blood vessel used for the bypass is sewn into to the coronary artery before the blockage and the other is at a site past the blockage creating a new path for blood to reach the heart. This procedure is repeated for each blocked vessel. The patient is removed from the heart-lung machine and the heart is started beating again, however, the patient is kept on a ventilator to aid in breathing. Once the heart is beating normally, drains are inserted in the chest, the sternum is wired back together, and the chest wall is closed.

QUESTIONS TO ASK YOUR DOCTOR

• Am I a candidate for minimally invasive CABG?
• How many of these procedures have you done in the past year?
• How many of these procedures are done in this hospital in a year?
• How urgent is my condition? I would like to get a second opinion.
• When will I be able to go back to work?
• Can you refer me to social services that can assist me and my family during my recovery?

Alternatives to traditional CABG

In some cases, it is possible to perform what is known as an “off-pump” CABG. In this situation, the heart-lung machine is not used. Instead, special equipment holds the tissue immobile where the graft is being placed while the rest of the heart continues to pump. Eliminating the heart-lung machine reduces the risk of complications. This technique is suitable for about 20% of patients. The surgeon may not know if an off-pump procedure is possible until the chest is opened and the coronary arteries are exposed.

Minimally invasive cardiac bypass surgery is also appropriate for a small percentage of patients. In this case, the incision is much smaller, the breastbone is not broken, and recovery is faster. Some minimally invasive CABG is now robot-assisted. Patients should discuss with their surgeon whether they are good candidates for an alternative CABG procedure.

Preparation

Before CABG is recommended, the patient will have had a variety of diagnostic cardiac tests to diagnose CAD. These tests include an echocardiogram , electrocardiogram (EKG), stress test , and coronary angiogram.

A few weeks before surgery, the doctor may have the patient begin taking aspirin daily. This helps keep blood clots from forming in the graft. Beta-blocker drugs may also be started a week or so before surgery. Immediately before the surgery, a repeat EKG, blood tests, and a chest x ray are performed. The patient will also meet with a cardiac anesthesiologist who will review the patient's health, medications, and past experience with anesthesia.

KEY TERMS

Anesthesia —Acombination of drugs administered by a variety of techniques by trained professionals that provide sedation, amnesia, analgesia, and immobility adequate for the accomplishment of the surgical procedure with minimal discomfort to the patient.

Angina —Also called angina pectoris, chest pain or discomfort that occurs when diseased blood vessels restrict blood flow to the heart.

Angiogram —An x-ray (radiographic) study of the blood vessels. An angiogram uses a radiopaque substance, or contrast medium, to make the blood vessels visible under x ray.

Anticoagulant —Pharmaceuticals to prevent clotting proteins and platelets in the blood to be activated to form a blood clot.

Aorta —The main artery that carries blood from the heart to the rest of the body. The aorta is the largest artery in the body.

Arrhythmia —An abnormal heart rhythm.

Artery —A vessel that carries oxygen-rich blood to the body.

Atrium (plural atria) —The right or left upper chamber of the heart.

Balloon angioplasty —A surgical procedure is done to stretch and widen the opening of a valve or to reopen a partially blocked artery so that blood can flow through it again at a normal rate. A tiny tube (catheter) is threaded through blood vessels to the point of the blockage. The catheter contains a balloon that is then expanded to stretch and open the artery.

Beta blocker —An anti-hypertensive drug that limits the activity of epinephrine, a hormone that increases blood pressure.

Coronary arteries —These are the first arteries to branch off the aorta (the large artery leaving the heart). They take oxygen-rich blood to the heart muscle. Blockage of these arteries can cause atherosclerosis and heart attack.

Coronary artery disease —Also called atherosclerosis; it is a build-up of fatty matter and debris in the coronary artery wall that causes narrowing of the artery.

Echocardiogram —A non-invasive imaging procedure used to create a picture of the heart's movement, valves, and chambers.

Electrocardiogram (EKG) —A noninvasive test records the electrical activity of the heart and is useful is assessing general heart health.

Graft —To implant living tissue surgically. Also refers to the tissue that is transplanted.

Heart-lung or cardiopulmonary bypass machine —A machine that replaces the function of the heart and lungs during open heart surgery by diverting blood flow away from the right atrium, adding oxygen to the blood, and returning blood beyond the left ventricle, to bypass the heart and lungs. This allows the heart to stop beating during surgery.

Mammary artery —A chest wall artery that descends from the aorta and is commonly used for bypass grafts.

Plaque —Fatty material that is deposited on the inside of the arterial wall.

Radial artery —An artery located in the arm and used for bypass grafts.

Saphenous vein —A long vein in the thigh or calf commonly used for bypass grafts.

Stent —A device made of expandable, metal mesh that is placed (by using a balloon catheter) at the site of a narrowing artery; the stent stays in place to keep the artery open.

Sternum —Also called the breastbone, the sternum is the bone in the chest that is separated during open heart surgery.

Stress test —A test that involves an electrocardiogram during rest and exercise to determine how the heart responds to stress.

Vein —A blood vessel that returns oxygen-depleted blood from various parts of the body to the heart.

Ventricle —A lower pumping chamber of the heart. There are two ventricles, right and left. The right ventricle pumps oxygen-poor blood to the lungs to be re-oxygenated. The left ventricle pumps oxygen-rich blood to the body.

Aftercare

Following a traditional CABG operation, the patient remains on a ventilator and under intensive monitoring in the intensive care unit (ICU) until he or she can breathe without assistance. Usually the ventilator is removed the day after surgery. After spending a day or two in the ICU, the patient is moved to a special cardiac unit where monitoring continues. Once stable, the patient then spends three to five more days in the hospital gaining strength. During this time the patient is encouraged to walk and move, sees a physical therapist , a respiratory therapist, and is given information about the recovery process and necessary lifestyle changes such as quitting smoking , reducing stress , and eating a diet low in fats and high in fruits, vegetables and whole grains. The patient will also be prescribed drugs such as anticoagulants, beta-blockers, and statins that will most likely be taken long term. After discharge from the hospital , it takes 4–8 weeks for recovery, although the breastbone will not heal for about 13 weeks, and heavy lifting should be avoided during that time.

Complications

As with any surgery, there is always a risk of excessive bleeding, infection, and a negative reaction to anesthesia. Other complications include the development of heart arrhythmias , heart attack, blood clot formation, and stroke during or soon after the procedure. Death is possible and occurs in about 3% of patients. The risk of serious complication and death is higher in individuals with damaged heart muscle, diabetes, chronic lung disease, and chronic kidney failure .

Results

After CABG, about 90% of patients no longer experience chest pain (angina ), and the quality of their life is substantially improved. Cardiac bypass surgery does not cure atherosclerosis, and the graft may become clogged and angina may return. In people with arterial grafts, about 80% remain pain free and have unobstructed grafts after 5 years, 50% at 10 years, and 25% at 15 years. For people with venous grafts, 70% have obstruction-free grafts after 5 years.

Caregiver concerns

In the operating room, open heart surgery requires a large team including a lead cardiovascular or cardiothoracic surgeon, assisting surgeons, a cardiovascular anesthesiologist, a perfusion technologist to oversee the heart-lung machine, and cardiovascular nurses. In addition, during the hospital stay, the patient will be cared for by ICU nurses, a respiratory therapist, physical therapist, nutritionist , and cardiac rehabilitation educator.

Resources

BOOKS

Sheridan, Brett C. So You're Having Heart Bypass Surgery. Hoboken, NJ: John Wiley, 2003.

Trahair, Richard C. All About Heart Bypass Surgery. New York: Oxford University Press, 2002.

OTHER

“Coronary Artery Bypass Surgery.” Mayo Clinic. June 15, 2006 [cited April 1, 2008]. http://www.mayoclinic.com/health/coronary-bypass-surgery/HB00022.

“Heart Disease: Bypass Surgery.” Web MD. December 1, 2006 [cited April 1, 2008]. http://www.webmd.com/heart-disease/heart-disease-bypass-surgery.

Sundt, Thoralf M. “CABG Information.” Society of Thoracic Surgeons. [cited April 1, 2008]. http://www.sts.org/sections/patientinformation/adultcardiacsurgery/cabg/index.html?CFID=1069995&CFTOKEN=93407768.

“What is Cardiac Bypass Surgery?” eHealthMD. October 2004 [cited April 1, 2008]. http://www.ehealthmd.com/library/cardiacbypass/CB_whatis.html.

ORGANIZATIONS

American College of Cardiology, Heart House, 2400 N Street, NW, Washington, DC, 20037, (202) 375-6000, (800) 253-4636 x8603, (202) 375-7000, [email protected], http://www.acc.org.

American Heart Association, 7272 Greenville Avenue, Dallas, TX, 75231, (800) 242-8721, http://www.americanheart.org.

National Heart Lung and Blood Institute Health Information Center, P.O. Box 30105, Bethesda, MD, 20824-0105, (301) 592 8573; TTY: (240) 629 3255, (240) 629 3246, [email protected], http://www.nhlbi.nih.gov.

Society of Thoracic Surgeons, 633 N. Saint Clair Street, Suite 2320, Chicago, IL, 60611, (312) 202-5800, (312) 202-5801, [email protected], http://www.sts.org.

Tish Davidson A. M.