Instantaneous Wave-Free Ratio in Acute Coronary Syndrome
Guideline Recommendations
- The American College of Cardiology and European Society of Cardiology recommend the use of iFR or FFR to guide the decision to proceed with PCI in patients with ACS, undocumented ischemia, and angiographically intermediate stenoses, with a Class I, Level A recommendation 1, 2, 3
- The 2021 ACC/AHA/SCAI and 2024 ESC guidelines provide Class I, Level A recommendations for iFR use in ACS, placing it on equal footing with FFR 1, 2
Key Trial Evidence
- The DEFINE-FLAIR and iFR-SWEDEHEART trials demonstrated that iFR-guided PCI was noninferior to FFR-guided PCI for clinical outcomes in patients with acute coronary syndromes 1, 2, 4, 5
Clinical Outcomes and Safety Data
- A critical finding emerged at 5-year follow-up: meta-analyses revealed a 2% absolute increase in all-cause mortality in patients managed with iFR compared to FFR 2, 6
- However, this mortality difference was not associated with increased rates of unplanned revascularization or non-fatal myocardial infarction, suggesting the mechanism remains unclear 2, 6
Practical Advantages
- iFR does not require adenosine administration, eliminating hyperemic agent-related adverse effects, procedural time, and cost 1, 3
- In the DEFINE-FLAIR and iFR-SWEDEHEART trials, iFR use was associated with lower rates of procedure-related chest pain and shorter procedural time compared to FFR 1, 4
Diagnostic Thresholds and Accuracy
- iFR ≤0.89 indicates hemodynamically significant stenosis requiring revascularization 1, 2, 3
- iFR >0.89 supports deferral of PCI in stable patients with intermediate stenoses 1, 3
Clinical Decision Algorithm
- Intermediate stenoses (40-90% diameter stenosis by visual estimate) in non-culprit vessels or stabilized culprit vessels where ischemia documentation is lacking are suitable for iFR assessment 1, 2
- Multivessel disease in ACS where determining which non-culprit lesions require treatment is uncertain is another indication for iFR use 7, 8