Coronary computed tomographic angiography

Computed tomography of the heart
Intervention
Image of contrast enhanced dual-source coronary CT-angiograph
ICD-9-CM	87.41
OPS-301 code	3-224
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Computed tomography or heart CT scan (CT coronary angiogram) is a procedure used to assess the extent of occlusion in the coronary arteries, usually in order to diagnose coronary artery disease. The patient is injected with an intravenous dye (iodine) and then their heart is scanned using a high speed CT scanner, allowing radiologists to assess the blood flow to their heart muscle.

Faster CT machines, due to multidetector capabilities, have made imaging of the heart and circulatory system very practical in a number of clinical settings. The faster capability has allowed the imaging of the heart with minimal involuntary motion, which creates motion blur on the image, and has a number of practical applications. It may be useful in the diagnosis of suspected coronary heart disease, for follow-up of a coronary artery bypass, for the evaluation of valvular heart disease and for the evaluation of cardiac masses.

It is uncertain whether this modality will replace invasive coronary catheterization. At present, it appears that the greatest utility of cardiac CT lies in ruling out coronary artery disease rather than ruling it in. This is because the test is highly sensitive (over 90% detection rate), so a negative test result largely rules out coronary artery disease (i.e. the test has a high negative predictive value). The test is not very specific, however, so a positive result is less conclusive and will need to be confirmed by subsequent invasive angiography.

The positive predictive value of cardiac CTA is approximately 82% and the negative predictive value is around 93%. This means for every 100 patients who appear to have coronary artery disease after CT angiography, 18 of them actually won't have it, and that for every 100 patients who have a negative CT angio test result (i.e. the test says they do not have coronary artery disease), 7 will actually have the disease.