Functional Lesion Assessment of Indeterminant Stenosis to Guide Revascularization - DEFINE-FLAIR

Contribution To Literature:

The DEFINE-FLAIR trial showed that iFR was noninferior to FFR at preventing adverse cardiac events.


The goal of the trial was to evaluate if functional lesion assessment by instantaneous wave-free ratio (iFR) would be noninferior to fractional flow reserve (FFR) among patients with stable angina or acute coronary syndromes.

Study Design

  • Randomized
  • Parallel

Patients undergoing functional assessment of an indeterminant coronary lesion were randomized to iFR (n =1,242) versus FFR (n =1,250). Revascularization was recommended if the iFR value was ≤0.89 or the FFR value was ≤8.0.

  • Total number of enrollees: 2492
  • Duration of follow-up: 12 months
  • Mean patient age: 66 years
  • Percentage female: 23%
  • Percentage with diabetes: 30%

Inclusion criteria:

  • Patients with stable angina or acute coronary syndrome (unstable angina or non-ST-segment elevation myocardial infarction [STEMI])
  • Indeterminant coronary stenosis 40-70% (nonculprit vessel in acute coronary syndrome patients)

Other salient features/characteristics:

  • Radial access: 72%
  • Mean iFR: 0.91
  • Mean FFR: 0.83
  • Mean number of vessels evaluated: 1.51 with iFR vs. 1.55 with FFR (p = 0.42)
  • Functionally significant lesions: 28.6% with iFR vs. 34.6% with FFR (p = 0.004)
  • Mean number of stents: 0.66 with iFR vs. 0.72 with FFR (p = 0.09)

Principal Findings:

The primary outcome, incidence of all-cause death, MI, or unplanned revascularization at 12 months, occurred in 6.8% of the iFR group versus 7.0% of the FFR group (p < 0.001 for noninferiority). The results were the same among tested subgroups.

Secondary outcomes:

  • Death: 1.9% for iFR vs. 1.1% for FFR
  • MI: 2.7% for iFR vs. 2.4% for FFR
  • Unplanned revascularization: 4.0% for iFR vs 5.3% for FFR
  • Patient-reported adverse procedural symptoms: 3.1% with iFR vs. 30.8% with FFR


Among patients undergoing functional determination of an indeterminant coronary stenosis for stable or unstable coronary disease, iFR was noninferior to FFR. The threshold to revascularize was ≤0.89 for iFR and ≤0.80 for FFR. Adverse cardiac events were similar between study groups. There were less patient-reported adverse procedure symptoms in the iFR group. The preferential use of iFR alone (not a hybrid iFR/FFR approach) over FFR for assessment of indeterminant lesions can be considered.


Davies JE, Sen S, Dehbi HM, et al. Use of the Instantaneous Wave-free Ratio or Fractional Flow Reserve in PCI. N Engl J Med 2017;376:1824-34.

Editorial: Bhatt DL. Assessment of Stable Coronary Lesions. N Engl J Med 2017;376:1879-81.

Presented by Dr. Justin E. Davies at the American College of Cardiology Annual Scientific Session (ACC 2017), Washington, DC, March 18, 2017.

Clinical Topics: Acute Coronary Syndromes, Cardiac Surgery, Invasive Cardiovascular Angiography and Intervention, Stable Ischemic Heart Disease, Cardiac Surgery and SIHD, Interventions and ACS, Interventions and Imaging, Angiography, Nuclear Imaging, Chronic Angina

Keywords: ACC17, ACC Annual Scientific Session, Acute Coronary Syndrome, Adenosine, Angina, Stable, Angiography, Cause of Death, Constriction, Pathologic, Coronary Stenosis, Cost-Benefit Analysis, Fractional Flow Reserve, Myocardial, Myocardial Infarction, Myocardial Revascularization, Random Allocation, omega-Chloroacetophenone

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