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

Cost-effectiveness: Total costs were estimated at $7,442 with iFR versus $8,243 with FFR (p = 0.021).


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. iFR was cost-effective compared with FFR. The preferential use of iFR alone (not a hybrid iFR/FFR approach) over FFR for assessment of indeterminant lesions can be considered for assessment of myocardial ischemia.


Presented by Dr. Manesh Patel at the American College of Cardiology Annual Scientific Session (ACC 2018), Orlando, FL, March 10, 2018.

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: ACC18, 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 Ischemia, Myocardial Revascularization, Random Allocation, omega-Chloroacetophenone

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