How is coronary artery disease diagnosed?
The resting electrocardiogram (EKG) is a recording of the electrical activity of the heart, and can demonstrate signs of oxygen starvation of the heart (ischemia) or heart attack. Often, the resting EKG is normal in patients with coronary artery disease and angina. Exercise treadmill tests are useful screening tests for patients with a moderate likelihood of significant coronary artery disease (CAD) and a normal resting EKG. These stress tests are about 60 to 70% accurate in diagnosing significant CAD.
If the stress tests do not reveal the diagnosis, greater accuracy can be achieved by adding a nuclear agent (thallium or Cardiolite) intravenously during stress tests. Addition of the nuclear imaging agent 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 significant artery narrowing in that region.
Combining echocardiography (ultrasound imaging of the heart muscle) with exercise stress testing (stress echocardiography) is also a very accurate technique to detect CAD. When a significant blockage exists, the heart muscle supplied by this artery does not contract as well as the rest of the heart muscle. Stress echocardiography and nuclear stress tests are both at least 80% to 85% accurate in detecting significant coronary artery disease.
When a patient cannot undergo exercise stress test because of nervous system or joint problems, medications can be injected intravenously to simulate the stress on the heart due to exercise and imaging can be performed with a nuclear camera or ultrasound.
Cardiac catheterization with angiography (coronary arteriography) 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 two main heart arteries (left and right). Iodine contrast, "dye," is then injected into the arteries while an X-ray video is recorded.
A newer modality, high speed CT scanning angiography has recently become available. This procedure uses powerful X-ray methods to visualize the arteries to the heart. Its role in the evaluation of CAD is currently being evaluated. For more, please read the CT Scanning Angiography article.