Coronary Artery Bypass Graft (cont.)
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.
For more, please read the CT Scanning
Angiography article.
Next: How is coronary artery disease (CAD) treated? »
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