Neil Osterweil

November 11, 2017

DENVER, CO — Two novel imaging systems that use angiographic information and hemodynamic modeling to emulate pressure-wire measurements were shown to provide diagnostic information about coronary stenosis in patients with angina that is on a par with that obtained through the more invasive fractional flow reserve (FFR) technique[1,2].

The studies—FAVOR II China and FAVOR II Europe-Japan—used different quantitative flow ratio (QFR) systems to assess stenosis without a pressure wire and without inducing hyperemia.

In FAVOR II China, both the patient-level and vessel-level diagnostic accuracy of QFR was above 92%, and an offline analysis showed that the diagnostic accuracy was 93.3%, reported Dr Bo Xu (National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences, Beijing, China) here at TCT 2017.

FAVOR II China "demonstrates clinical utility of QFR for use in diagnostic catheterization laboratories, and QFR bears the potential of improving angiography-based identification of functionally significant stenosis during coronary angiography," Xu said.

In FAVOR II Europe-Japan, QFR was shown to offer better sensitivity and specificity for the detection of functionally significant coronary lesions compared with two-dimensional quantitative coronary angiography (2D-QCA) using FFR as a reference standard, concluded Dr Jelmer Westra (Aarhus University Hospital, Aarhus, Denmark) and colleagues, in a study also reported here.

QFR is a method for estimating FFR based on fluid dynamic equations and emulated hyperemic flow velocity. It is computed from lumen contours in two standard angiographic progressions more than 25° apart. Data on contrast-flow velocity is estimated by frame count during baseline conditions.

The still-experimental technique is also faster than standard techniques.

"The median time to QFR was 4.8 minutes, while median time to FFR was 7 minutes, so QFR was statistically significantly faster in this study," Westra said.

FAVOR II China

Results of FAVOR II China were published online October 31, 2017 in Journal of the American College of Cardiology.

Investigators in the multicenter trial enrolled 308 patients with one or more lesions with diameter stenosis from 30% to 90% and reference diameter 2 mm or greater by visual estimation. Online QFR and FFR results were captured in 328 of 332 interrogated vessels. QFR, QCA, and wire-based FFR results were assessed by blinded observers online during coronary angiography procedures, and the results were reanalyzed offline by an independent core laboratory.

Online QFR and QCA assessments, blinded to investigators who measured FFR, were obtained in 329 vessels of the 306 patients, and wire-based FFR measurements were obtained from 330 vessels, also in 306 patients.

The lesions studied included bifurcation lesions in 24.7%, tortuous vessels in 14.2%, moderate or severely calcified lesions in 18.4%, thrombotic lesions in 0.3%, and tandem lesions in 46.3%

For the primary end point of diagnostic accuracy of online QFR—defined as a consistency ratio of QFR-evaluated outcomes (≤0.8 or >0.8) with the reference standard FFR-evaluated outcomes (≤0.8 or >0.8)—to identify hemodynamically significant coronary stenosis, the point estimate for accuracy was 92.7% (95% CI 89.3%–95.3%), far exceeding the prespecified lower limit of the confidence interval of 75% (P<0.0001).

The diagnostic accuracy in different interrogated vessels ranged from 91.0% for the right coronary artery, 92.4% for the left anterior descending artery, and 96.4% for the left circumflex artery. There were no significant differences in accuracy in any between-vessel comparisons.

In both online and offline analyses of QFR and QCA, QFR showed a high degree of accuracy, sensitivity, specificity, and both positive and negative predictive value (P<0.0001 for each category).

Xu acknowledged that further study will be needed before QFR can be accepted as a replacement for FFR in the cath lab.

"As clinical decisions in the study population were based on FFR measurements, it was not possible to directly evaluate clinical outcome by a QFR-based diagnostic strategy. Randomized trials comparing clinical outcomes after QFR-based diagnostic strategies and standard diagnostic strategies are warranted," he said.

The QFR system used in this trial was AngioPlus (Pulse Medical Imaging Technology, Shanghai, China).

FAVOR II Europe-Japan

The FAVOR II Europe-Japan study was designed to test the hypothesis that "QFR has superior sensitivity and specificity for detection of functional significant lesions in comparison with 2D-QCA with FFR as the gold standard," Westra said.

In the investigator-initiated observational study, paired acquisition of FFR and computation of QFR were performed in 310 patients in 11 hospitals in Europe and Japan.

QFR met its primary end point of superior sensitivity and specificity compared with 2D-QCA. The sensitivity for QFR was 88%, compared with 46% for 2D-QCA (P<0.001) and the respective specificities were 88% vs 77% (P<0.001).

As noted before, acquisition time was significantly faster with QFR than FFR (P<0.001).

Westra agreed with Xu that randomized clinical trials are needed to determine where a QFR-based diagnostic strategy can provide clinical outcomes not inferior to those of pressure-wire–based strategies.

In both a briefing and in the first-report abstract session where Xu and Westra presented their data, discussants commented that the results looked quite good and questioned whether comparative outcome trials were really necessary.

"The statement has been made that we need outcome studies with it; do we really?" asked Dr Ori Ben-Yehuda (Cardiovascular Research Foundation, New York City), who moderated the briefing.

"We actually show that the two measurements are identical. Why do we need another outcome study?" he asked, noting that outcome studies aren't necessary with new blood-pressure devices.

"To take Ori's analogy a little bit further, I think it's our uncertainty when it comes to the patient blood-pressure cuff at home, vs an ambulatory blood-pressure measurement, vs an office blood-pressure measurement and the implications of each of those. So I think it's more than just accuracy and time—it still is going to be something that I think has to be evaluated," said Dr Duane S Pinto (Beth Israel Deaconess Medical Center, Boston), a discussant at the briefing.

"We're seeing a technology here that is somewhat disruptive," said Dr Alexandra J Lansky (Yale School of Medicine, New Haven, Connecticut), a discussant at the abstract session.

"It really can be used in all cath labs and really takes away all the complications associated with invasive FFR assessment. I would question whether we do need clinical-outcome studies. Do we need that? We have very consistent results here with very high accuracy. Do we need to go to clinical outcome?" she said.

But discussant Dr Gary S Mintz (Cardiovascular Research Foundation) asked Westra whether editing of arterial contours was allowed in the lab during the trial. Westra acknowledged that contour editing did take place in some cases, although he was uncertain how many.

"That to me is an important limitation to the whole technology," Mintz replied. "I would feel much more confident and comfortable with relying on this technology without a clinical trial and outcomes data if this were automatically generated. Once you begin to start having any observer editing of the contours, then I begin to wonder how much bias gets introduced during the study."

FAVOR II CHINA was supported by Pulse Medical Imaging Technology. FAVOR II Europe-Japan was supported by Aarhus University. Xu disclosed off-label investigations of new devices but did not disclose specific companies. Disclosures for the coauthors are listed in the paper. Westra reported no relevant financial relationships. Ben-Yehuda disclosed fees from Cardiovalve. Pinto disclosed grant/research contract with Amarin and consultant fees/honoraria from and speaker's-bureau membership for Abbott Vascular, Medtronic, Boston Scientific, Chiesi, Abiomed, and the Medicines Company. Mintz disclosed research support from St Jude Medical, Boston Scientific, and Volcano and consultant fees/honoraria from and  speaker's-bureau membership for Boston Scientific, ACIST, and InfraReDx.

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