Instantaneous wave-free ratio (iFR) is noninferior to fractional flow reserve (FFR) for identifying hemodynamically significant coronary artery stenoses during angiographic evaluation for revascularization.
Results of 2 clinical trials: the Functional Lesion Assessment of Intermediate Stenosis to Guide Revascularisation (DEFINE-FLAIR; ClinicalTrials.gov identifier: NCT02053038) and Instantaneous Wave-free Ratio vs Fractional Flow Reserve in Patients with Stable Angina Pectoris or Acute Coronary Syndrome (iFR-SWEDEHEART; ClinicalTrials.gov identifier: NCT02166736) were simultaneously presented at the 66th Annual Scientific Session & Expo of the American College of Cardiology ,March 17-19, 2017, Washington, DC, and published in the New England Journal of Medicine.1,2
The ability to determine whether a coronary artery lesion is flow-limiting is crucial for making decisions regarding whether or not to revascularize a patient.1 FFR accomplishes this task by measuring the pressure gradient across the lesion during hyperemia, which is induced with a vasodilator such as adenosine.2 Even though FFR assesses pressure rather than flow, it serves as a surrogate for flow and its use has been associated with better outcomes after percutaneous coronary intervention (PCI).1
iFR is similar to FFR in that it also assesses the pressure gradient across the coronary lesion, but it does so during diastole and without the need for administering a hyperemic agent.2 Limited data suggest that using a vasodilator may not be necessary for evaluating stenosis severity and that FFR is not superior to iFR.1
DEFINE-FLAIR and iFR-SWEDEHEART were randomized controlled trials that examined whether iFR is noninferior to FFR for guiding coronary revascularization. These studies were led by Justin E. Davies, MBBS, PhD, from Imperial College London in England, and Matthias Götberg, MD, PhD, from Skane University Hospital in Lund/Malmo, Sweden, respectively.1,2
Both studies enrolled more than 2000 patients with coronary artery disease (n=2492 for DEFINE-FLAIR and n=2037 for iFR-SWEDEHEART) who were randomly assigned to revascularization guided by iFR or by FFR. The primary end point for both studies was composite nonfatal myocardial infarction, unplanned revascularization, or all-cause death within 1 year post-procedure.1,2
Similar numbers of patients in the iFR and FFR groups experienced the primary end point in DEFINE-FLAIR (6.8% vs 7.0%) and in iFR-SWEDEHEART (6.7% vs 6.1%). iFR met noninferiority criteria in both studies.1,2
Rates of death from any cause were also similar in the treatment groups of both studies.1,2
Conversely, rates of procedure-related signs and symptoms differed significantly in the 2 treatment arms.1,2 In DEFINE-FLAIR, compared with FFR, “iFR [was] associated with 10 times fewer procedural patient symptoms and signs (such as bronchospasm/rhythm disturbances),” Dr Davies told Cardiology Advisor.
In iFR-SWEDEHEART, significantly fewer patients in the iFR group experienced chest discomfort during the procedure than in the FFR group (3.0% vs 68.3%; P <.001).2
DEFINE-FLAIR also found that iFR could be performed more quickly than FFR (40.5 min vs 45.0 min; P =.001).1 While procedure times were similar in both groups, in iFR-SWEDEHEART, significantly more lesions were assessed in the iFR group than in the FFR group, Dr Götberg noted in an interview with Cardiology Advisor.
He believes the reason for the higher number of lesions evaluated with iFR “was that the threshold for performing physiology in multivessel disease was lower when using iFR (due to an instantaneous measurement without discomfort).”
“DEFINE-FLAIR and iFR-SWEDEHEART are … the first physiology studies performed in real world patient populations, so [their findings] are generalizable to clinical patients,” Dr Davies said.
DEFINE-FLAIR and iFR-SWEDEHEART were funded by Phillips Volcano.
- Davies JE, Sen S, Dehbi HM, et al. Use of the instantaneous wave-free ratio or fractional flow reserve in PCI. [published online March 18, 2017]. N Engl J Med. doi:10.1056/NEJMoa1700445
- Götberg M, Christiansen EH, Gudmundsdottir IJ, et al; for the iFR-SWEDEHEART Investigators. Instantaneous wave-free ratio versus fractional flow reserve to guide PCI. [published online March 18, 2017]. N Engl J Med. doi:10.1056/NEJMoa1616540