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MUNICH -- Using CT imaging to assess the hemodynamic significance of coronary lesions is "promising" but needs more research before it displaces conventional invasive fractional flow reserve (FFR), researchers said.

Using FFR as the reference standard, FFR_CT plus CT angiography (CTA) had good sensitivity (90%) and negative predictive value (84%) on a per patient basis for detecting ischemia, which indicates a low rate of false-negative studies, according to James K. Min, MD, of Cedars-Sinai Heart Institute in Los Angeles, and colleagues.

Although FFR_CT plus CTA were superior to CTA alone, the specificity (54%) and negative predictive value (67%) of the combination remained low compared with conventional FFR, indicating that a considerable number of false-positive studies would endure, Min reported here during a Hot-Line session at the European Society of Cardiology meeting.

The results of this proof of concept study show that FFR_CT can "impart considerable discriminatory power" to detect and exclude ischemia in patients with suspected CAD, Min said.

However, future studies should be conducted to determine the cost-effectiveness of FFR_CT in guiding decisions to stent, particularly given the potentially high false-positive rate, he added.

“Non-invasive FFR is a dream for all interventional cardiologists," said study discussant Jean-Pierre Bassand, MD, of the University Hospital Jean-Minjoz in Besançon, France. Although Bassand praised the DeFACTO study, he expressed concern about the discrepancy between the accuracy of FFR versus FFRCT.

For example, compared with FFR, the sensitivity and specificity of FFRCT in cases of greater than 90% or less than 30% stenosis were 83% and 76%, respectively. The per-vessel correlation of FFRCT to FFR was 0.63.

“What matters is the correlation with FFR," he concluded.

A single non-invasive imaging test that can identify obstructive coronary artery disease (CAD) and determine the physiological significance of those lesions would be ideal. At present, nuclear stress imaging fulfills the first part, but it cannot label stenoses as hemodynamically significant or not. Also, nuclear stress testing suffers from high rates of both false-negative and false-positive studies, Min said.

The results of this study are in line with stress imaging: per patient diagnostic accuracy of 73% (95% CI 67% to 78%). Min said that studies are being designed to compare FFR_CT plus CTA with stress imaging.

"For patients considered for invasive therapy, this type of test could help exclude those who don't need to be stented," Spencer King III, MD, of St. Joseph's Hospital in Atlanta told 木瓜直播.

"The excitement about this CT approach is that it moves things closer to being able to assess physiology and anatomy in a single non-invasive test," added King, who is also a past president of the American College of Cardiology.

However, the process of calculating the FFR values from CT data currently takes about 6 hours, Min told 木瓜直播. The CT data are sent offsite to HeartFlow, the company that makes the software. Whether such processing would be done onsite in the future is not yet determined, Min said. He also expects the processing time to drop to about 2 hours by the year’s end.

HeartFlow has already received EU mark to use the software in Europe and is in the process of applying for FDA approval, Min said.

Conventional FFR uses a pressure wire inserted through the groin to the coronary arteries to determine the hemodynamic significance of lesions. The same data can be gleaned during a typical CTA exam with software that calculates computational fluid dynamics without additional radiation exposure. The median radiation exposure among the study centers was 6.4 mSv (range 4.4 to 15 mSv).

The original FAME study found the use of FFR to guide stenting was better than relying on angiography alone in patients with multivessel disease. A second study, FAME II, was stopped early because of the overwhelming benefit seen in patients with stable CAD when FFR guided stenting versus patients randomized to optimal medical therapy.

Because FFR_CT is a novel technique, it has not been adequately evaluated in its ability to identify patients with ischemia, Min said.

The researchers therefore designed the DeFACTO (Determination of Fractional Flow Reserve by Anatomic Computed Tomographic Angiography) study, which sought to evaluate the accuracy of FFR_CT while using invasive FFR as the reference standard.

The study was also simultaneously published online in the Journal of the American Medical Association.

The 252 patients with suspected or known CAD were recruited from 17 centers in five countries between October 2010 and October 2011. They were scheduled to undergo diagnostic catheter angiography.

The mean age of patients was 63, 70% were men, and a majority were white. Nearly half of the patients had obstructive CAD (>50% stenosis).

Among 615 study vessels, 271 had less than 30% stenosis and 101 had at least 90% stenosis. Invasive coronary angiography and FFR identified 46.5% of 408 vessels with obstructive CAD, while CT and FFR_CT identified 52.3% of 406 vessels.

A total of 172 patients had an FFR value <0.80, which indicates an ischemic lesion.

The diagnostic accuracy of FFR_CT plus CT was 73% (95% CI 67% to 78%), but this did not meet the prespecified primary endpoint of greater than 70% of the lower bound of the 95% confidence interval, Min said.

However, Min emphasized that FFR_CT was superior to CTA alone in all categories.

The researchers concluded that the results show the potential of FFR_CT as a "promising" non-invasive tool to identify ischemia.

King added that despite not meeting the prespecified primary endpoint, "it's an encouraging early study."