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Coronary artery disease

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of CAD.

Alternative Names

Angina; Atherosclerosis; Heart disease

Diagnosis

Many tests can diagnose possible heart disease. The choice of which (and how many) tests to perform depends on the patient's risk factors, history of heart problems, and current symptoms. Usually the tests begin with the simplest and may progress to more complicated ones.

Routine Tests to Determine Risk for Heart Disease

Doctors routinely check for high blood pressure and unhealthy cholesterol levels in all older adults. Specific tests are also important in people who may have risk factors or symptoms of diabetes. Doctors may also test for homocysteine, the protein albumin, and blood clotting factors, especially fibrinogen.

Electrocardiograms (ECGs)

An electrocardiogram (ECG) measures and records the electrical activity of the heart. Between 25 - 50% of people who suffer from angina or have silent ischemia, however, have normal ECG readings. The waves measured by the ECG correspond to the contraction and relaxation pattern of the different parts of the heart. Specific waves seen on an ECG are named with letters:

• P. The P wave is associated with the contractions of the atria (the two chambers in the heart that receive blood from outside).
• QRS. The QRS is a series of waves associated with ventricular contractions. (The ventricles are the two major pumping chambers in the heart.)
• T and U. These waves follow the ventricular contractions.

The most important wave patterns in diagnosing and determining treatment for heart disease and heart attack are called ST elevations and Q waves.

• A depressed or horizontal ST wave suggests some blockage and the presence of a heart disease, even if there is no angina present. (This finding, however, is not very accurate, particularly in women, and can occur without heart problems).
• ST elevations and Q waves are the most important wave patterns in diagnosing and determining treatment for a heart attack. They suggest that an artery to the heart is blocked, and that the full thickness of the heart muscle is damaged. ST segment elevations do not always mean the patient has a heart attack. And, some heart attack patients do not have elevated ST segments. Other factors are important in making a diagnosis.

Exercise Stress Test

The primary value of exercise stress tests is not to detect coronary artery disease but to help determine the severity and predict the outcome of an existing heart condition. It is considered for the following people:

• Patients with possible or probable angina and low or intermediate risk for adverse heart events.
• Selected adults who do not have symptoms of heart disease but are at moderate risk to high risk for developing heart disease (a 10 - 20% chance within 10 years). Moreover, heart blockage without angina (silent ischemia) may suggest a more severe condition, at least in men.

Basic Procedure. A stress test (exercise tolerance test) monitors the patient's heart rhythms, blood pressure, and clinical status. It can tell how well the heart handles work and if parts of the heart have decreased blood supply. A typical stress test involves:

• The patient walks on a treadmill or rides a stationary bicycle. Exercise continues until the heart is beating at least 85% of its maximum rate, until symptoms of heart trouble occur (changes in blood pressure, heart rhythm abnormalities, angina, fatigue), or the patient simply wants to stop.
• For patients who cannot exercise, the doctor may administer dobutamine or arbutamine, which are drugs that simulate the stress of exercise.
• An ECG is used to monitor heart rhythms during a stress test. (An echocardiogram or more advanced imaging technique may also be used to visualize the actions of the heart and blood flow.)

More than 25% of patients stop exercising before they reach their own maximum limits because of fear of a heart event. Patients should be reassured that the activities performed in the test under the guidance of a professional are safe.

Interpreting Results. To accurately assess heart problems, experts look at a number of findings derived from the ECG and other tools during exercise. They include:

• Exercise capacity. This is a measure of a person's capacity to reach certain metabolic rates.
• Heart rate and ST waves. On ECGs, doctors specifically look for abnormalities in part of the wave tracing called an ST segment. A certain type of ST segment depression may suggest the presence of heart disease. However, gender, drugs and other medical conditions can affect the ST segment. Using a measurement that adjusts the ST segment to heart rate improves accuracy.
• Dukes Treadmill Score. This important score uses the number of minutes a patient can exercise and other factors that are present in patients with exercise-limiting angina.
• Heart rate recovery.
• Chronotropic index. This is the percentage of the heart-rate reserve that is used during the exercise. A result of 80% or less suggests a significant risk for serious heart problems in most patients.
• Changes in systolic blood pressure.

Using these and other measures, doctors can determine risk fairly accurately, particularly for men of any age with chronic stable angina. The test has limitations, however, and some are significant. For example, a 2002 study indicated that in patients with suspected unstable angina the chances for a future adverse heart event remain high even if the exercise test shows low risk. In addition, for many reasons, the test is less accurate in women, and an echocardiogram may be a more accurate procedure for them. About 10% of patients, particularly younger people, will have false positive test results. In such cases, test results indicate abnormalities when there are no heart problems.

Echocardiograms

An echocardiogram is a noninvasive test that uses ultrasound images of the heart. This test is more expensive than an ECG, but it can be very valuable, particularly when used with a stress test, to detect the location and extent of heart muscle damage. It appears to be more accurate for women than ECG stress tests, but at this time it is not routinely recommended as a replacement for most women.

Computed Tomography

Computed tomography (CT) scans used alone or with ECG may be used to detect calcium deposits on the arterial walls, which are strong indicators of current and future coronary artery disease. The presence of calcium does not always signify narrowing of the arteries. But, the absence of calcification in the arteries indicates the patient has no risk for heart disease.

Advanced CT techniques are improving accuracy:

• Electron Beam Computed Tomography. Electron beam computed tomography (EBCT)  is a CT technique that scans the heart so quickly that the motion of the heart appears frozen. This procedure identifies calcification and stratifies cardiac risk accurately.
• Helical Multislice Computed Tomography. Another CT technique called helical multislice computed tomography (MSCT) angiography is able take pictures of the entire heart in one millimeter slices in the time it takes for a patient to hold one breath. It is highly accurate but exposes the patients to a higher radiation levels than EBCT.

Some expert groups recommend CT scans in selected patients who have an intermediate risk (10 - 20% chance of heart disease within 10 years). For some of these patients, EBCT may be a better first choice than exercise stress testing. In general, the use of these expensive imaging tests are probably not very helpful in people at low or high risk. (In people with high risk, the additional information from these tests would not add much value.) More research is needed to determine the benefits of CT scanning in specific individuals.

Radionuclide Imaging

Radionuclide procedures use imaging techniques and computer analyses to plot and detect the passage of radioactive tracers through the region of the heart. Such tracing elements are typically given intravenously. Radionuclide imaging is useful for diagnosing and determining:

• Severity of unstable angina when less expensive diagnostic approaches are unavailable or unreliable
• Severity of chronic coronary artery disease
• Success of surgeries for coronary artery disease.
• Whether a heart attack has occurred

Various imaging techniques may be used with radionuclide procedures, including:

• Planar scintigraphy uses a special overhead camera and is the oldest scanning technique.
• Single-photon emission computed tomography (SPECT) uses a camera that rotates around the patient and takes pictures of "slices" of the heart. It is more accurate than planar imaging in precisely locating problems in the arteries.
• Positron-emission tomographic (PET) scanners employ multiple rings that surround the patients, which detect and record atomic particles (photons) that are emitted by the tracer elements (such as radioactive oxygen, nitrogen, or carbon). It is more expensive and less widely available than SPECT.

Myocardial Perfusion (Blood Flow) Imaging Test (also called the Thallium Stress Test). This radionuclide test is typically used with an exercise stress test to determine blood flow to the heart muscles. It is a reliable measure of severe heart events. It may be useful in determining the need for angiography if CT scans have detected calcification in the arteries. About a minute before the patient is ready to stop exercising, the doctor administers a radioactive tracer into the intravenous line. (Tracers include thallium, technetium, or sestamibi.) Immediately afterwards, the patient lies down for a heart scan, usually with a planar scintigraphy or with SPECT. If the scan detects damage, more images are taken 3 or 4 hours later. Damage due to a prior heart attack will persist when the heart scan is repeated. Injury caused by angina, however, will have resolved by that time.

Radionuclide Angiography. This is a technique for visualizing the chambers and major blood vessels of the heart. It uses an injected radioactive tracer and can be performed during exercise, at rest, or with use of stress-inducing drugs. It is an excellent test for assessing the heart's pumping action and for determining the severity of coronary artery disease. It is an alternative to echocardiograms in certain situations.

Other Investigative Noninvasive Imaging Techniques

Magnetic Resonance Angiography (MRA). MRA is a very promising noninvasive imaging technique that can provide three-dimensional images of the major arteries to the heart and identify disease with high accuracy. Experts believe this approach will eventually be a good alternative to angiography.

Angiography

Angiography is an invasive test. It is used for patients who show strong evidence for severe obstruction on stress and other tests, and for patients with acute coronary syndrome.

• A narrow tube is inserted into an artery, usually in the leg or arm, and then threaded up through the body to the coronary arteries.
• A dye is injected into the tube, and an x-ray records the flow of dye through the arteries.
• This process provides a map of the coronary circulation, revealing any blocked areas.

Major complications include stroke, heart attacks, and kidney damage. These risks are very low (about 0.1%), however, if the procedure is done in an experienced medical center (one that performs at least 300 of these operations every year). Allergic reactions can also occur. The procedure is expensive, and between 10 - 30% of patients who have this procedure have normal results.

Biologic Markers

When heart cells become damaged, they release different enzymes and other molecules into the blood stream. Elevated levels of such markers of heart damage in the blood or urine may help predict a heart attack in patients with severe chest pain and help determine treatment. Some of these factors include:

• Troponins. The proteins cardiac troponin T and I are released when the heart muscle is damaged. Both are proving to be among the best diagnostic indications of heart attacks. They help to identify many individuals with ACS who might otherwise be misdiagnosed.
• Creatine kinase myocardial band (CK-MB). CK-MB has been a standard marker, but the MB fraction is not as accurate as troponin levels, since elevated levels can appear in people without heart injury.
• Myoglobin. Myoglobin is a protein found in heart muscles. It is released early in the injured heart, and it may be useful in combination with CK-MB and the troponins.

• Review Date: 4/12/2006
• Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital

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