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iFR vs FFR — EECC MCQ

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ModerateCoronary Artery DiseaseiFR vs FFREECC

A 68-year-old man undergoes elective PCI. The operator uses iFR (instantaneous wave-free ratio) instead of FFR to assess an intermediate stenosis. What is the key difference between iFR and FFR?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: A — iFR is measured during a specific period of diastole (the wave-free period) when microvascular resistance is naturally low and stable, without requiring adenosine-induced hyperaemia — threshold for significance is ≤0.89

iFR (instantaneous wave-free ratio) measures the ratio of distal to proximal coronary pressure during a specific diastolic window (the 'wave-free period') when competing pressure waves are quiescent and microvascular resistance is naturally low. Unlike FFR, iFR does NOT require adenosine to induce maximal hyperaemia, offering: (1) faster measurement; (2) avoidance of adenosine side effects (chest pain, dyspnoea, AV block); (3) cost savings. The DEFINE-FLAIR and iFR-SWEDEHEART trials demonstrated that iFR-guided PCI was non-inferior to FFR-guided PCI for clinical outcomes. Treatment threshold: iFR ≤0.89 = significant (PCI recommended); iFR >0.89 = defer. The 2024 ESC CCS Guidelines give iFR equal Class I recommendation alongside FFR for physiological lesion assessment.

Reference: ESC (2024): CCS Guidelines; DEFINE-FLAIR/iFR-SWEDEHEART Trials