The electrocardiogram (EKG) is a recording of the electrical activity of the heart muscle and can detect heart muscle 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 a useful screening tool 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 an exercise stress test. The addition of thallium allows nuclear imaging with an external camera of blood flow to different regions of the heart. 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 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 an 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 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 a 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:
- Allergic reaction to iodine
- Risks to 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
- who have symptoms suspicious of coronary disease
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