Reed Miller

July 23, 2012

July 23, 2012 (Baltimore, Maryland) — A large "real-world" study found that asymptomatic individuals undergoing coronary computed tomography angiography (CCTA) have worse risk-factor profiles and a higher coronary disease burden than their symptomatic counterparts [1].

At the Society of Cardiovascular Computed Tomography 2012 Annual Scientific Meeting, Dr Kavitha Chinnaiyan (William Beaumont Hospital, Royal Oak, MI) presented results from a 21 573-patient study from the Advanced Cardiovascular Imaging Consortium (ACIC) registry intended to compare the overall diagnostic yield of CCTA in asymptomatic and symptomatic patients.

"In this cohort, it's very concerning that these patents had more disease when they were asymptomatic," she said. "When the patient walks in, can I say whether the patient has disease based on symptoms alone? The answer is no, and that's concerning. We lack good clinical algorithms [to diagnose disease based on symptoms]," she told heartwire .

When the patient walks in, can I say whether the patient has disease based on symptoms alone? The answer is no.

She pointed out that the CONFIRM registry showed that CT has incremental value over calcium scoring for predicting the patient's prognosis, but "this study shows that when used for diagnosis, CCTA findings do not correlate to stenosis very well." In the current study, the best predictor of coronary disease was a coronary artery calcium score greater than 400. So the diagnostic value of the CCTA over and above coronary calcium scoring remains unclear, Chinnaiyan said.

"We need to establish the utility of CCTA over calcium scoring. In this patient population, we really didn't miss a lot of over-50% stenosis in people with a high calcium score, so the question now is to find the population that benefits from a CT but not a calcium score," she said. "The general feeling is that these would probably be the younger patients with a lot of risk that haven't yet developed calcification, but that is something that needs to be teased out in population studies."

Asymptomatic Patients Look Worse on CCTA

Currently, the multisociety appropriate-use criteria for cardiac CT list CCTA of asymptomatic individuals as inappropriate for patients at low or intermediate risk of coronary disease and uncertain for patients at high risk. Nevertheless, many asymptomatic patients in this registry did undergo CCTA, Chinnaiyan explained, either as a screening test (1275 patients) or after a stress test (1264 patients).

The study found that, compared with the symptomatic patients, the asymptomatic patients had a lower frequency of normal coronaries on CCTA (38% vs 51.2%) and a higher frequency of both stenosis >50% diameter (21% vs 16.3%) and stenosis <50% diameter (51% vs 40.2%) (p<0.001 for all comparisons).

A >50% stenosis was found on CCTA in 23% of asymptomatic patients with prior stress tests, only 19% of asymptomatic patients with no prior stress tests, and 16.3% of symptomatic patients.

Multivariable predictors of >50% stenosis on CCTA were about the same for both the asymptomatic and symptomatic groups. In both groups, men were about 2.7 times as likely to have a >50% stenosis than the overall cohort. Other risk factors predicting >50% stenosis in both groups were diabetes, hypertension, and dyslipidemia.

The study also looked at three-month "downstream" outcomes to see whether CCTA scans of these patients led to greater resource utilization. The study found that the patients who were symptomatic at the beginning of the study came back to the hospital more often but that the patients most likely to undergo angiography or revascularization were those with the most severe coronary disease. The study also estimated the patients' total exposure to radiation and found that the patients who'd undergone a nuclear stress test prior to CT had the highest estimated dose--around 30 mSv on average--and much higher than that of patients who underwent only CT.

That high dose for patients undergoing stress testing first is "very concerning," so CCTA could someday prove to be a better way to screen these patients without exposing them to high radiation, Chinnaiyan said. But more studies are needed to identify a patient population in whom CCTA provides more diagnostic accuracy than calcium scoring alone.