Coronary CTA Can Serve as Gatekeeper to Invasive Angiography

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In patients with suspected coronary artery disease (CAD), coronary computed tomographic angiography (CTA) can serve as a gatekeeper for invasive angiography following stress testing, according to research published in the February 14, 2012, issue of the Journal of the American College of Cardiology.

Kavitha M. Chinnaiyan, MD, of the William Beaumont Hospital (Royal Oak, MI), and colleagues prospectively studied 6,198 patients without known CAD who were being treated at 47 centers in Michigan. All were referred for CTA within 3 months of a stress test. The investigators looked at how well demographics, risk factors, symptoms, and stress test results correlated with the presence of obstructive CAD, defined as greater than 50% stenosis.

The indication for CTA was symptoms suggestive of ischemia in 82.6% of the cohort, while 17.4% were tested due to cardiac risk factors. Most had abnormal stress tests (58.5%), although 24.9% had normal and 16.6% had equivocal results.

CTA testing found that only 18.7% of patients had obstructive CAD. Independent predictors of disease included male sex, current smoking, older age, hypertension, and typical angina (table 1).

Table 1. Independent Predictors of Obstructive CAD on CTA

 

OR

95% CI

Male Sex

2.37

1.83-3.06

Current Smoking

2.23

1.57-3.17

Age (per 10-year increment)

2.14

1.89-2.41

Hypertension

1.80

1.37-2.34

Typical Angina

1.48

1.03-2.12


Surprisingly, stress test results did not independently predict obstructive CAD on CTA.

Among the 621 patients who underwent invasive angiography, there was a strong correlation between the angiographic findings and CTA (OR 9.09; 95% CI 5.57-14.8, P < 0.001). But no such relationship existed between the results of angiography and stress testing (OR 0.79; 95% CI 0.56-1.11, P = 0.17).

Expanding the Scope of CTA

In a telephone interview, Dr. Chinnaiyan told TCTMD, “We’re really trying to establish the best practice of CT.”

Dr. Chinnaiyan cited a 2010 paper published in the New England Journal of Medicine that demonstrated a “very low diagnostic yield” with elective angiography in 40,000 patients. Based on this,s he said, “we clearly need to find better ways to identify people who really need to go to the cath lab, and CT seems to be a very effective gatekeeper. We know from multiple prognostic studies that if there is a normal CT, the warranty period is about seven years.”

According to an editorial by Pim J. de Feyter, MD, and Koen Nieman, MD, both of Erasmus Medical Center (Rotterdam, the Netherlands), the current study results seem to confirm the utility of CTA as just such a gatekeeper.

“Presuming that 80% (4,650 of 6,198) of the patients with equivocal or abnormal test would be referred to [invasive angiography], adjudication to [coronary CTA] decreased referral to 20%, indeed an effective gatekeeper,” they write. “Overall, the approach of adjudication of conflicting stress results was successful and led to a diagnostic yield [with invasive angiography] of 57% to detect > 50% stenosis, which is an improvement over previous data, but still lower than desirable.”

Robert S. Schwartz, MD, of the Minneapolis Heart Institute and Foundation (Minneapolis, MN), noted in a telephone interview with TCTMD that the study, “really reflects what most of us that do CT already understand, but the world hasn’t quite gotten there yet.”

“CT is a technology that’s underappreciated by the general community,” he commented, adding that the test “fits very early into clinical evaluation of a patient with suspected disease or the asymptomatic patient that you’re concerned about because of elevated traditional risk factors.”

The Right Test for the Right Question

The poor ability of stress testing to identify disease was a surprise based on previous studies that were “performed in controlled conditions with standardized reading formats and readers,” Dr. Chinnaiyan noted. “This is what’s happening in the real world.” She emphasized, though, that stress testing can still complement anatomic testing.

When choosing a test, practicing clinicians should consider which question they need to answer, Dr. Schwartz advised. “The nuclear test is a functional test,” he added. “It looks at the consequences of stenosis. CT, at least in its present form, is an anatomic test. So to see differences between function and anatomy is not surprising.”

But advances in technology may change the landscape. The ongoing DeFACTO (Determination of Fractional Flow Reserve by Anatomic Computed Tomography Angiography) trial is designed to assess whether the use of computational fluid dynamic modeling of the coronary arteries based on CT can provide fractional-flow reserve measurements via a non-invasive test.

In the meantime, the present study “also gives insight into how CT is being used right now and where it should and shouldn’t be used,” said Dr. Chinnaiyan. “For example, we’ve always said that we shouldn’t be using CT in asymptomatic patients. However, in our paper, we actually found that asymptomatic patients who had a positive stress test had more disease on CT than symptomatic patients. That raises the question as to whether our guidelines should be more specific about which asymptomatic patients should not get CT. We definitely need better risk stratification systems.”

 


Sources:
1. Chinnaiyan KM, Raff GL, Goraya T, et al. Coronary computed tomography angiography after stress testing: Results from a multicenter, statewide registry, ACIC (Advanced Cardiovascular Imaging Consortium). J Am Coll Cardiol. 2012;59:688-95.

2. de Feyter PJ, Nieman K. Computed tomography coronary angiography: A noninvasive escape when stress tests fail (caught between guidelines and gut feeling). J Am Coll Cardiol. 2012;59:696-7.

 

 

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Coronary CTA Can Serve as Gatekeeper to Invasive Angiography

In patients with suspected coronary artery disease (CAD), coronary computed tomographic angiography (CTA) can serve as a gatekeeper for invasive angiography following stress testing, according to research published in the February 14, 2012, issue of the Journal of the American
Disclosures
  • The study was sponsored and funded by the Blue Cross/Blue Shield/Blue Care Network of Michigan (BCBSM).
  • Drs. Chinnaiyan, de Feyter, Nieman, and Schwartz report no relevant conflicts of interest.

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