Coronary Artery Disease Screening Tests (CAD) (cont.)
Radionucleide Stress Test
Radionucleide stress testing involves injecting a radioactive isotope
(typically thallium or cardiolyte) into the patient's vein after
which an image of the patient's heart becomes visible with a special
camera. The radioactive isotopes are absorbed by the normal heart
muscle. Nuclear images are obtained in the resting condition, and
again immediately following exercise. The two sets of images are then
compared. During exercise, if a blockage in a coronary artery results
in diminished blood flow to a part of the cardiac muscle, this region
of the heart will appear as a relative "cold spot" on the nuclear
scan. This cold spot is not visible on the images that are taken
while the patient is at rest (when coronary flow is adequate).
Radionucleide stress testing, while more time-consuming and expensive
than a simple ECST, greatly enhances the accuracy in diagnosing CAD.
Stress Echocardiography
Another supplement to the routine ECST is stress echocardiography.
During stress echocardiography, the sound waves of ultrasound are
used to produce images of the heart at rest and at the peak of
exercise. In a heart with normal blood supply, all segments of the
left ventricle (the major pumping chamber of the heart) exhibit
enhanced contractions of the heart muscle during peak exercise.
Conversely, in the setting of CAD, if a segment of the left ventricle
does not receive optimal blood flow during exercise, that segment
will demonstrate reduced contractions of heart muscle relative to the
rest of the heart on the exercise echocardiogram. Stress
echocardiography is very useful in enhancing the interpretation of
the ECST, and can be used to exclude the presence of significant CAD
in patients suspected of having a "false-positive" ECST.
What if patients are unable to exercise adequately for an ECST?
Many patients are unable to exercise maximally for stress testing due
to a variety of conditions including arthritis, severe lung disease,
severe cardiac disease, orthopedic conditions, and diseases of the
nervous system. In such patients, pharmacological stress testing is
often employed.
Next: Physiologic Stress Test »
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