NEW YORK (Reuters Health) – Computed tomography coronary angiography (CTCA) is most usefully applied in patients with intermediate risk for disease, because it will identify the ones who need more invasive testing, researchers say.

That’s because CTCA is not necessary when stress testing suggests a low likelihood of disease, and patients with a high risk Duke clinical score should go straight to invasive angiography, they say.

In the Annals of Internal Medicine for May, senior author Dr. Pim J. de Feyter, from Erasmus University Medical Center, Rotterdam, the Netherlands, and associates describe their observational study of 517 patients (mean age 58.9) referred for evaluation of chest symptoms. All underwent stress testing and CT coronary angiography. Between 2004 and 2006, the first 297 patients also had invasive angiography. Between 2006 and 2008, 141 low-risk patients (i.e., those with negative results on both tests) did not go on to invasive testing.

The researchers analyzed the tests for their clinical utility, which they defined as “a pretest or posttest probability that suggests how to proceed with testing.” The authors used the Duke clinical score to determine pre-test probability of coronary artery disease. They assumed that a post-test disease probability of 5% or less meant no further testing was required, a probability between 5% and 90% indicated uncertainty, and a post-test disease probability of 90% or more meant the patient should be sent directly for invasive angiography.

Not surprisingly, CTCA was more accurate than stress testing, with a sensitivity of nearly 100%, they report.

With a low pretest probability (< 20%), a negative result on stress testing or CTCA suggested no need for invasive angiography. In patients with an intermediate pretest likelihood of disease (20-80%), a positive CTCA was linked with a 93% probability of disease, whereas a negative CTCA suggested no need for additional tests.

In patients with a high pretest probability of disease (>80%), noninvasive testing only confirmed disease in most of these patients, showing a post-test disease probability of 91%.

The investigators recommend stress testing in patients with low pretest likelihood of disease based on its safety, low cost, and absence of ionizing radiation. This test may also provide objective evidence of ischemia before revascularization is performed.

The authors admit their study was subject to referral bias. The authors also note that lesions seen on coronary angiography are not always functionally significant, “so the comparisons may have produced estimates of accuracy that make CTCA seem more accurate and clinically useful than it really is.”

The authors believe CTCA should be a first-line diagnostic test for intermediate-risk patients because it is sufficiently accurate to stop testing or proceed with invasive coronary angiography.

Still, they recommend additional research, including cost-benefit analyses, before CTCA is routinely recommended for these patients.

Reference:
Ann Intern Med 2010;152:630-639.