Key Points:
- Quantitative Flow Reserve (QFR) is a non-pressure wire method of assessing flow through the coronary arteries, using 3D reconstructions and computations from the angiogram.
- 3825 patients across several centers in China were randomized to receive PCI by standard angiography versus QFR guidance, in which stents were placed for vessels with QFR <0.8.
- At one year, MACCE was significantly lower in the QFR group compared to the standard angiography group (5.8 vs. 8.8%).
- Study authors suggest the use of QFR will increase over pressure-wire guided physiology due to its ease of use.
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The use of fractional flow reserve in the assessment of ischemia has increased over the past decade, as it has made its way into the guidelines for coronary revascularization. Some argue that it is still underutilized, and blame several factors for this: the need for a wire, which could introduce procedural complications; the added cost of the FFR wire and system; as well as added procedural time and the need for heparin. In a late breaking session at the 33rd annual TCT conference, Dr. Bo Xu (Beijing, China) presented the findings of FAVOR III, a trial in which a novel physiologic assessment tool was used to guide PCI strategy in patients presenting to the cardiac catheterization lab.
Quantitative Flow Reserve (QFR) is an angiography-based physiologic measurement of coronary flow. Using high quality angiograms from two orthogonal views of each vessel, a three-dimensional reconstruction of the vessel is created. After inputting TIMI flow, a flow reserve measurement is calculated using the principles of fluid dynamics. Hyperemia and anticoagulation are not required for accurate measurements.
Investigators of FAVOR III China sought to answer whether standard use of QFR to guide PCI conferred any benefit over angiography alone, as did the current gold standard, FFR. In this multi-center sham-controlled, blinded randomized trial, participants undergoing coronary angiography for stable angina, unstable angina, and myocardial infarction were randomized to receive either QFR-guided PCI or standard angiography-guided PCI. After coronary angiography demonstrated at least one epicardial vessel of 2.5 mm reference diameter with 50-90% stenosis, participants were randomized in a 1:1 fashion. In the QFR arm, any qualifying lesion was assessed with QFR. If the QFR was >0.80, PCI was deferred, and if ≤0.80, PCI was performed. Participants and clinical assessors were blinded in the following fashion: participants were given headphones with music to wear during the length of the procedure; a 10 minute delay for QFR and sham calculation was implemented in both arms before the PCI; QFR results were not allowed into the medical record; and personnel involved in the PCI were precluded from participation in follow up.
At one year, 1905 participants in the QFR group and 1897 in the standard group were available for follow up. Participants were mostly men with a mean age of 63 years. Smoking, hyperlipidemia, and diabetes were present in a third of either arm, while hypertension was present in two thirds. 58% of either group underwent the procedure for unstable angina, and 25.8% of each group underwent angiography for stable angina. Multi-vessel disease was present in more than half of participants.
QFR Guidance Changed Strategy
The use of QFR did have an impact on whether PCI was undertaken. Of the vessels that were intended to be treated, 19.6% were deferred based on negative QFR values, compared to only 5.2% in the angiography group. 4.4% of vessels not initially intended to be treated were treated after receiving positive QFR values.
Results
At one year, MACE event rates were lower in the QFR-guided group compared to the angiography-guided group at 5.8% vs. 8.8% (HR 0.65 [95% CI 0.51 – 0.83], p = 0.004). The secondary outcome of MACE excluding peri-procedural MI
followed suit, with a decrease in event rates from 4.8% to 3.1 % (HR 0.64 [95% CI 0.46 – 0.89], p = 0.0073). There was no significant difference in the two groups when it came to other secondary endpoints, including periprocedural MI, target vessel revascularization and stent thrombosis.
In an interview with Dr. C. Michael Gibson, Dr. Bo Xu commented on the results, stating that he hopes to see a shift toward the use of QFR-guided PCI, as the technology is widely available in cardiac catheterization laboratories across China. “The benefit of a quick, 3 minute analysis, without the need for a wire or added procedural complications makes this strategy the most favorable method of hemodynamic assessment,” he stated before adding “It also ensures that patients are getting PCI for the right reasons”. Some limitations of the study were its enrollment of lower risk patients as well as the lower rates of coronary imaging during PCI. The study was simultaneously printed in Lancet.