The resting electrocardiogram (EKG) is a recording of the electrical activity of the heart, and can show changes caused by ischemia or a heart attack. Often, the EKG in patients with coronary artery disease is normal at rest, and only becomes abnormal when heart muscle ischemia is brought on by exertion. Therefore, exercise treadmill or bicycle testing (stress tests) are useful screening tests for patients with significant coronary artery disease (CAD) and a normal resting EKG.
These stress tests are 60 to 70% accurate in diagnosing significant CAD.
If the stress tests are not enough to diagnose the problem, a nuclear agent (Cardiolite® or thallium) can be given intravenously during stress tests. Addition of one of these agents allows imaging of the blood flow to different regions of the heart, using an external camera. An area of the heart with reduced blood flow during exercise, but normal blood flow at rest, signifies substantial artery narrowing in that region.
Stress echocardiography combines echocardiography (ultrasound imaging of the heart muscle) with exercise stress testing. It is also an accurate technique for detecting CAD. When a significant narrowing exists, the heart muscle that is supplied by the narrowed artery does not contract as well as the rest of the heart muscle. Stress echocardiography and thallium stress tests are 80% to 85% accurate in detecting significant CAD.
When a patient cannot undergo an exercise stress test because of neurological or arthritic difficulties, medications can be injected intravenously to simulate the stress on the heart normally brought on by exercise. Heart imaging can be performed with either 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 coronary arteries. Iodine contrast "dye" is then injected into the arteries while an X-ray video is recorded. Coronary arteriography gives the doctor a picture of the location and severity of narrowed artery segments. This information is important in helping the doctor select medications, PCI, or coronary artery bypass graft surgery (CABG) as the preferred treatment option.
A newer, less invasive technique is high-speed CT coronary angiography. While it still involves radiation and dye exposure, no catheters are needed, which decreases the risk of the procedure somewhat. This is a very new treatment, and its role in the evaluation and management of CAD is still evolving. It is important to remember that the risk of serious complications from conventional coronary angiography is very low (well under 1%).
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