"Technologies that provide both a highly sensitive anatomic evaluation for obstructive disease and a highly specific physiologic evaluation for ischemia represent the ‘Holy Grail’ for noninvasive imaging for CAD," Dr. Manesh R. Patel wrote in an accompanying editorial (JAMA 2012 Aug. 26 [doi: 10.1001/2012.jama.11383]).
One possible investigational approach is the combination of anatomic analysis using CT and functional analysis using fractional flow reserve based on CT data (FFR-CT).
The DeFACTO investigators "raise the bar by comparing this diagnostic technology with a reference standard of both invasive angiography and invasive FFR. This change in reference standard may in part explain some of the accuracy findings. So how should these findings be considered with regard to current clinical evaluation for chest pain?" asked Dr. Patel.
It’s important to put the findings on the performance of CT angiography into context, he wrote. "Several recent multicenter studies have reported diagnostic performance of CT angiography to have high sensitivity (i.e., between 85%-95%) compared with conventional invasive angiography for stenoses of 50% or greater." The high sensitivity of CTA has been used to triage low-risk patients in acute settings.
"However, in stable intermediate-risk patients, for whom a higher degree of specificity (low rate of false positive results) may be desirable to reduce referrals for invasive angiography, concerns exist about the specificity of CT angiography," Dr. Patel noted. In the present study, CT angiography had a sensitivity of 84% but a specificity of only 42% with the more rigorous reference standard.
"It is in this context that FFR-CT represents a novel and important innovation, with the possibility not only to diagnose but also to help direct invasive treatment. The current ... multicenter report by Min et al. confirms a high sensitivity (90%) but demonstrates modest specificity (54%), albeit better than CTA alone," he wrote.
"At first glance, readers of the study may consider FFR-CT technology to be limited based on the results presented. However, this would be a naive conclusion, likely based on the published diagnostic performance of noninvasive tests compared only with invasive angiography," Dr. Patel warned. By comparing existing noninvasive imaging technologies with invasive angiography plus FFR, it is highly likely that the published diagnostic performance would be reduced. "In fact, in clinical practice, the sole use of invasive angiography for lesion evaluation has decreased. Additionally, in real-world practice, the current noninvasive technologies used for diagnosis and risk stratification in stable elective patients prior to invasive angiography do not perform at the published diagnostic levels, as evidenced by the low rates of obstructive CAD at elective catheterization. Hence, the current report describes an important noninvasive technology that may improve existing care and has the potential to outperform established noninvasive technologies," according to Dr. Patel.
DR. PATEL is the cardiology section leader in the peripheral vascular program at Duke University in Durham, N.C., and is assistant director of the cardiac catheterization laboratory. Dr. Patel reports consultancy for Bayer, Jansen, Baxter, and Otsuka, and grants from Johnson & Johnson and AstraZeneca.
