Coronary Flow Reserve — EECC MCQ

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ModerateCoronary Artery DiseaseCoronary Flow ReserveEECC

A 55-year-old woman with known stable angina is reviewed. Her cardiologist measures the coronary flow reserve (CFR) during invasive assessment of a moderate LAD stenosis. CFR is 1.8 (normal ≥2.0). What does this indicate?

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Correct answer: B — CFR <2.0 indicates impaired coronary flow reserve — the epicardial stenosis, microvascular dysfunction, or both are limiting maximal myocardial blood flow; this identifies physiologically significant disease warranting treatment

Coronary flow reserve (CFR) is the ratio of hyperaemic to resting coronary blood flow. Normal CFR is ≥2.0-2.5. A CFR <2.0 indicates impaired flow reserve, which can result from: (1) epicardial stenosis (reducing maximal achievable flow); (2) microvascular dysfunction (impaired arteriolar vasodilation — measured by the index of microvascular resistance, IMR >25); (3) both (combined epicardial + microvascular disease). Unlike FFR (which is specific to epicardial stenosis), CFR reflects the TOTAL coronary flow pathway (epicardial + microvascular). The 2024 ESC CCS Guidelines recommend CFR and IMR assessment as part of the comprehensive ANOCA/INOCA workup to identify the specific endotype of coronary dysfunction (epicardial stenosis, microvascular dysfunction, or vasospasm) and guide targeted therapy. CFR is measured invasively using a thermodilution or Doppler wire during adenosine hyperaemia.

Reference: ESC (2024): CCS Guidelines