Computed Tomographic Angiography in the Diagnosis of Coronary Artery Stenosis and for the Evaluation of Acute Chest Pain

COMPUTED TOMOGRAPHIC ANGIOGRAPHY IN THE DIAGNOSIS OF CORONARY ARTERY
STENOSIS AND FOR THE EVALUATION OF ACUTE CHEST PAIN
A Technology Assessment
INTRODUCTION
The California Technology Assessment Forum was requested to review the scientific evidence for the use of
cardiac computed tomographic angiography in the diagnosis of coronary artery stenosis and for the
evaluation of acute chest pain. This review was prompted by reports that there may be new information
about cardiac computed tomography published since this topic was evaluated by the Blue Cross Blue Shield
Association Technology Evaluation Center (BCBSA TEC) in August, 20061.
BACKGROUND
Coronary artery disease (CAD) is the number one cause of death in men and women. CAD is caused by atherosclerotic plaques developing in the coronary arteries. Many therapies have been shown to decrease CAD mortality, therefore early detection and treatment is critical.

The gold standard for defining coronary artery anatomy is angiography. During coronary angiography, a
catheter is introduced into the femoral, brachial or radial artery and is then passed up to the aorta. Iodinated
contrast dye is then directly injected into the coronary arteries, while digital X-ray images are taken.
Although the risks are generally considered low, there are some risks to the procedure. These include
bleeding and other complications at the catheter insertion site, catheter manipulation causing embolization
of plaque leading to stroke or myocardial infarction, dye related complications, including allergic reactions
and renal toxicity, and exposure to radiation, which may be associated with an increased risk of cancer2, 3.
Coronary artery computed tomography (CT) angiography (CTA) is a non-invasive technology that can
directly image coronary artery anatomy, while decreasing some of the risks associated with an invasive
procedure. It has been proposed as an alternative to coronary angiography. CTA requires the use of
contrast material (administered intravenously) and high speed high resolution CT machinery to take detailed
volumetric pictures of blood vessels.

There are several technical challenges involved in getting good images with CTA. First, the image must be
obtained in a short period of time to avoid blurring. Sometimes beta blockers are given before the
procedure to slow the heart down; therefore pictures can then be taken during diastole when motion is
reduced. Second, rapid scanning is best so that the images can be taken while the patient is holding his/her
breath. Third, thin sections enable higher quality images. Volumetric imaging is then performed and
enables multiple images to be reconstructed to fully demonstrate the coronary arteries.
Multidetector row CT (MDCT) scanning uses helical CT (rotating a tube around the patient to get continuous spiral images). They have multiple detectors – 4, 8, 16, 32, 40 or 64. Limitations of MDCT include: 1) it is harder to obtain good images with a fast heart rate, and 2) the distal portions of the coronary arteries are more difficult to see due to more motion artifact. Many of the earlier studies were done with 16 row MDCT, but MDCT with at least 32 rows is soon likely to become standard.

Important negative consequences of CTA are radiation exposure, which is significantly higher than
conventional angiography3, and nephrotoxicity from the dye. An additional potential complication is the
identification of incidental non-coronary lesions, which then require additional evaluation to determine their
significance.
Two potential uses of CTA are addressed in this report; 1) Use of CTA to diagnose coronary artery stenosis,
and 2) use of CTA in the evaluation of acute chest pain.
Use of CTA to diagnose coronary artery stenosis has the goal of determining whether or not patients have
significant stenoses of the coronary arteries, while avoiding an invasive procedure. CTA could be used as
an alternative to invasive angiography or as an additional noninvasive cardiac test that may be
complementary to other noninvasive tests routinely used (e.g. exercise stress tests). An important issue to
consider is whether or not it replaces other diagnostic tests or becomes an additional or additive test.
For patients with acute chest pain being evaluated in the emergency room, an important goal would be to exclude clinically significant CAD, so as to avoid unnecessary hospitalization. It would thus potentially be most useful in a low risk chest pain population.