Angina (cont.)
Why is it important to establish the diagnosis of angina?
Angina is usually a warning sign of the presence of significant coronary artery disease. Patients with angina are at risk of developing a
heart attack (myocardial infarction). A heart attack is the death of heart muscle precipitated by the complete blockage of a diseased coronary artery by a blood clot.
During angina, the lack of oxygen (ischemia) to the heart muscle is temporary and reversible. The lack of oxygen to the heart muscle resolves and the chest pain disappears when the patient rests. In contrast, the muscle damage in a heart attack is permanent. The dead muscle turns into scar tissue when healed. A scarred heart cannot pump blood as efficiently as a normal heart, and can lead to heart failure.
Up to 25% of patients with significant coronary artery disease have no symptoms at all, even though they clearly lack adequate blood and oxygen supply to the heart muscle. These patients have "silent" angina. They have the same risk of heart attack as those with symptoms of angina.
How is angina diagnosed?
The
electrocardiogram (EKG) is a recording of the electrical activity of the heart muscle, and can detect heart muscle which is in need of oxygen. The EKG is useful in showing changes caused by inadequate oxygenation of the heart muscle or a heart attack.
Exercise stress test
In patients with a normal resting EKG, exercise treadmill or bicycle testing can be useful screening tools for coronary artery disease. During an
exercise stress test (also
referred to as stress test, exercise electrocardiogram, graded exercise
treadmill test, or stress ECG), EKG recordings of the heart are performed continuously as the patient
walks on a treadmill or pedals on a stationary bike at increasing levels of
difficulty. The occurrence of chest pain during exercise can be correlated with changes on the EKG, which demonstrates the lack of oxygen to the heart muscle. When the patient rests, the angina and the changes on the EKG which indicate lack of oxygen to the heart can both disappear. The accuracy of exercise
stress tests in the diagnosis of significant coronary artery disease is 60% to 70%.
If the exercise stress test does not show signs of coronary artery disease, a nuclear agent (thallium) can be given intravenously during exercise
stress test. The addition of thallium allows nuclear imaging of blood flow to different regions of the heart, using an external camera. A reduced blood flow in an area of the heart during exercise, with normal blood flow to the area at rest, signifies significant artery narrowing in that region of the heart.
Stress echocardiography
Stress echocardiography combines echocardiography (ultrasound imaging of the heart muscle) with exercise
stress testing. Like the exercise thallium test, stress echocardiography is more accurate than an exercise
stress test in detecting coronary artery disease. When a coronary artery is significantly narrowed, the heart muscle supplied by this artery does not contract as well as the rest of the heart muscle during exercise. Abnormalities in muscle contraction can be detected by echocardiography. Stress echocardiography and thallium stress tests are both about 80% to 85% accurate in detecting significant coronary artery disease.
When a patient cannot undergo exercise stress test because of neurological or orthopedic difficulties, medications can be injected intravenously to simulate the stress on the heart normally brought on by exercise. Heart imaging can be performed with a nuclear camera or echocardiography.
Cardiac catheterization
Cardiac catheterization with angiography (coronary arteriography) is a technique that allows x-ray pictures to be taken of the coronary arteries. It is the most accurate test to detect coronary artery narrowing. Small hollow plastic tubes (catheters) are advanced under x-ray guidance to the openings of the coronary arteries. Iodine contrast "dye" is injected into the arteries while an x-ray video is recorded. Coronary arteriography gives the doctor a picture of the location and severity of coronary artery disease. This information can be important in helping doctors select treatment options.
CT coronary angiogram
CT coronary angiography is
procedure that uses an intravenous dye that contains iodine, and CT scanning to
image the coronary arteries. While the use of catheters is not necessary (thus
the term "noninvasive" test applies to this procedure), there are still some
risks involved, including the following:
- Patients allergic to iodine
- Patients with abnormal kidney function
- Radiation exposure which is similar to, if not greater than, that
received with a conventional coronary angiogram.
Nonetheless, this is generally a very safe test for most people. It is a major
tool in the diagnosis of coronary artery disease in patients:
- at high risk for developing coronary disease (cigarette smokers, those
with genetic risk, high cholesterol levels, hypertension, or diabetes),
- who have unclear results with exercise stress tests or other testing, or
- who have symptoms suspicious of coronary disease
Next: What are the treatment options for angina patients? »
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