Current CTA studies predict CAD risk in symptomatic, not asymptomatic patients

Marlene Busko

May 01, 2012

Montreal, QC - New analyses of data from the Coronary CT Angiography Evaluation for Clinical Outcomes International Multicenter (CONFIRM) registry of patients with symptomatic, suspected CAD sheds light on how coronary computed-tomography angiography (CTA) can affect patient management, said Dr Benjamin Chow (University of Ottawa Heart Institute, ON)[1]. He discussed "lessons learned" from recent publications based on the CONFIRM registry at the Society of Cardiovascular Computed Tomography (SCCT) Cardiac CT Imaging Day .

On the other hand, according to Dr Carolyn Taylor (St Paul's Hospital, Vancouver, BC), coronary CTA is not yet ready for prime-time risk stratification of asymptomatic patients with possible CAD[2].

CONFIRMing value of CTA in symptomatic patients

CONFIRM collected data from 12 centers in six countries, which provides sufficient power for retrospective analysis, said Chow.

In a study by Chow and colleagues, in close to 14 000 patients in the CONFIRM study who were followed for a median of 22.5 months, 271 patients died from all-cause mortality[3]. Patients without coronary atherosclerosis had an annualized mortality rate of 0.36% compared with an annualized mortality rate of 2.63% in patients who had high-risk CAD. The study showed that "CTA  . . . has incremental prognostic value [in predicting all cause-mortality] above and beyond the routine clinical predictors and LV ejection fraction [<50%]," he told heartwire . Patients with no CAD or nonobstructive CAD had an excellent prognosis, but those with high-risk CAD had a poor prognosis.

CTA -detected CAD and annual mortality

CTA detection Annual mortality (%)
No CAD 0.36
Non obstructive CAD 1.14
Non - high-risk CAD 1.41
High-risk CAD 2.63

"The take-home message is if you have a normal scan with no atherosclerosis, your prognosis is good, [which is] reassuring to the physician and the patient," Chow said. Patients with nonobstructive coronary atherosclerosis had slightly worse outcomes, which "teaches us that nonobstructive plaque, in a portion of individuals, causes trouble," he added. "The bottom line is if you have obstructive coronary artery disease, it certainly seems to signify that other investigations are needed."

In another study, the group reported that patients in the CONFIRM database had a lower-than-predicted prevalence of having at least a 50% diameter coronary stenosis (CAD 50). For example, among men aged 50 to 59 with chest pain and typical angina, patient-management guidelines predict that 93% would have CAD 50 (detected by CTA), but in the CONFIRM population, only 38% had CAD 50. This suggests there is population bias, whereby lower-risk patients are referred for CT angiography, said Chow[4].

A third study showed that among patients with suspected CAD who had a calcium score of zero, 13% had nonobstructive atherosclerosis and 3.5% had obstructive coronary disease (CAD 50)[5]. "If we rely only on the calcium score, we're missing a proportion of individuals with obstructive disease," said Chow.

Preliminary analysis from a new CONFIRM-based study suggests that statin therapy might improve outcomes in patients with nonobstructive coronary atherosclerosis, he added.

Value of CTA in asymptomatic patients unknown

Taylor, however, urged a much more cautious approach. "None of the guidelines are recommending CT angiography [for risk stratification in asymptomatic patients], because there's a paucity of data," Taylor told heart wire .

One study looked at 1000 middle-aged, asymptomatic Korean subjects (mean age of 50 years, 37% women) who underwent coronary CTA to detect CAD[6]. Most patients either had a low risk of CAD (55.7%) or a moderate risk of CAD (34.1%). "Despite this low risk, [the group found that] one in five [patients] had some coronary plaque," Taylor noted. In 17 months of follow-up, 15 events—mostly stent implantations—occurred, all in the patients with plaque. "On the basis of our results and considering present radiation exposure data, we cannot recommend that CTA be used as a screening tool in this population at this point," the authors concluded.

Another study showed that physicians were more likely to prescribe preventive therapies in low-risk patients in whom plaque was detected[7]. Among 1000 asymptomatic patients from a health-screening program, 225 patients (21%) had plaque. In patients with plaque, statin use increased 3.3-fold and aspirin use increased 4.2-fold; patients were more likely to have secondary tests and revascularizations.

In a small study, Taylor and colleagues examined data from 50 asymptomatic subjects (54% males) with a mean age of 53 years who were referred for CAD risk stratification. Preliminary findings showed that all subjects had evidence of plaque on coronary CTA, and most had normal coronary artery calcium scores.

There are now more sensitive tools that can detect mild plaque in patients with chest pain, Taylor explained. But what does this mean? How much occlusion is too much? Using coronary CTA to find plaque in asymptomatic patients "is not something to advocate for now, but it has interesting potential and needs to be explained," she said.

Chow has received research and fellowship support from GE Healthcare and educational support from TeraRecon.

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