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 thallium allows nuclear 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 thallium 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. Sometimes, an exercise study is then done to determine whether  a moderate narrowing (40 - 60%) is actually causing ischemia and, therefore, requires treatment.
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.