Coronary Artery Disease Screening Tests (CAD) (cont.)
Physiologic Stress Test
During a physiologic stress test, certain medications are
administered which stimulate the heart to mimic the physiologic
effects of exercise. One of these medications is dobutamine, which is
similar to adrenaline. Dobutamine is carefully administered to
gradually increase the heart rate and strength of the contractions of
the heart muscle. Simultaneously, echocardiography or radionucleide
imaging is performed. Alternatively, a medicine called adenosine is
administered, which simulates the physiology of the coronary artery
circulation during exercise. Adenosine is combined with radionucleide
isotope imaging to provide a very accurate test for the detection of
significant CAD. Pharmacological stress testing is commonly performed
in patients who are thought to be at high risk for significant CAD
and who are scheduled for major non-cardiac surgical procedures.
These patients are often unable to perform exercise stress testing
due to the underlying condition for which they require surgery. In
this setting, pharmacological stress testing is invaluable in
assessing the cardiac risk of patients prior to surgery.
Are there other tests for CAD that are noninvasive?
Ultrafast CT
A new (and controversial) noninvasive test for the detection of CAD
is electron beam computerized tomography, also known as Ultrafast
CT. Unlike the above mentioned stress tests that measure the heart's
physiology, Ultrafast CT is designed to measure calcium deposits in
the coronary arteries.
In patients with CAD, the
plaques which make up the blockages contain significant amounts of
calcium, which can be detected with Ultrafast CT. This test will identify
calcium in blockages as mild as 10-20%, which would not
be detected by standard physiological testing. When such mild
blockages are detected, however, the only recommended therapy
is risk factor modification (cholesterol lowering and cessation of smoking
if applicable), and adjunctive use of aspirin and certain vitamins -- such therapy would
be advised in all patients with risk factors for CAD, regardless of
the results of any noninvasive tests. A potential limitation of
Ultrafast CT is that a "calcium score" for each vessel is reported,
and this is not entirely lesion specific - several minor blockages in
a given vessel may result in a similar vessel score as one severe
blockage in a vessel.
The major value of Ultrafast CT appears to be for screening of young
patients with one or more risk factors for the development of CAD.
Ultrafast CT scanning is of limited value in older patients, in whom
some degree of calcification is commonly found. Additionally, for the
reasons described above, the detection of some calcification may not
be reflective of significant CAD.
Next: What is the most accurate method of defining CAD? »
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