Coronary CT Finds Prognostically Dire CAD in Otherwise Very Low-Risk Patients

March 06, 2013

VANCOUVER — Unobstructive and even obstructive CAD is fairly common at coronary computed-tomographic (CT) angiography in patients with suspected coronary disease but no modifiable CV risk factors, such as dyslipidemia or hypertension. Moreover, even under those low-risk conditions by standard measures, cardiovascular risk goes up significantly for patients who have such disease by CT angiography.

Those observations, based on an international registry cohort, suggest that CT angiography could have a role to play in triaging such patients to undergo further, possibly more invasive diagnostic testing, according to researchers in a report published online February 19, 2013 in Radiology[1].

"These are patients who, by many risk calculators, would be considered relatively low risk and are often a difficult population to assess," Dr Jonathon Leipsic (University of British Columbia, Vancouver) told heartwire .

Prognostically Important and Powerful

"They would typically be referred for noninvasive testing first, either nuclear testing or treadmill testing, to further increase the likelihood of a positive angiogram--should you go that route--but also for risk stratification." But those tests can disclose only CAD that is advanced enough to cause ischemia, he noted. That's not the case with CT angiography, which was prognostic even in patients with mild CAD or none.

"The thing about CT is that you're no longer guessing. You can identify mild disease, and you can also identify significant coronary artery narrowings, and then on that basis better understand the downstream prognosis of these patients," Leipsic said.

"For those reasons, in an appropriately selected patient population, with atypical symptomatology and some suspicion of coronary disease, I think CT is a very good first-line test. What's important in our analysis is that even when symptoms were atypical and the patient had no cardiovascular risk factors, some of them still had significant coronary disease, and when they did, it was prognostically important and powerful."

Referred Due to Symptoms or Family History

The study's 5262 patients represented those without modifiable risk factors (smoking, hypertension, dyslipidemia, or diabetes) in a 12-center prospective cohort of >12 000 patients without known CAD who were referred for coronary CT angiography. Referral was made based on symptoms or "clinical concern often due to the pres­ence of a family history of CAD." About 36% of patients were asymptomatic.

CAD was classified as obstructive (>50% stenoses) in 12%, nonobstructive (>1% to 49% of luminal diameter) in 27%, and absent in 61%.

After a follow-up averaging 2.3 years, the primary end point of major adverse cardiac events (MACE)--death, nonfatal MI, unstable angina, or late (>90 days) target-vessel revascularization--occurred in 106 patients (2.0%).

The risk-adjusted MACE hazard ratio (HR) for obstructive CAD was 6.64 (95% CI 3.68–12.00, p<0.001). The HR varied from 11.9 (p<0.001) for patients with symptoms to 6.3 (p<0.001) for those without symptoms.

The MACE risk varied by number of coronary vessels with obstructive disease: HR of 6.11 (p<0.001) for one vessel, 5.86 (p<0.0001) for two vessels, and 11.69 (p<0.001) for three vessels.

Filling an Unmet Need?

The use of coronary CT angiography has a good deal of traction in emergent settings based on supportive clinical trials, but not without controversy. Its use in stable patients is more of a frontier.

Leipsic and his colleagues acknowledge that the guidelines "generally do not support imaging testing for individuals who are at low risk for obstructive CAD," nor are the current findings "intended to suggest modification of current appropriate-use criteria."

But their study highlights the fact that "at present, no clinical risk score exists to help guide clinicians as to the risk of incidence of MACE in sta­ble patients suspected of having CAD."

Leipsic discloses being on the board of GE Healthcare and Vital Images, consulting for Edwards Lifesciences and GE Healthcare, and serving on the speaker's bureau for GE Healthcare, all for reasons "not related to the present article." The other authors had no disclosures.