Coronary physiology assessment in the catheterization laboratory

Table 2 Main parameters available to assess coronary macrovascular and microvascular circulation

Technique	Cutoff value	Implications	Commentary
CFR	< 2	Unspecific macrovascular and microvascular inability to increase flow	Patients with CFR > 2 have favorable outcomes
FFR	≤ 0.8	Functionally significant epicardial stenosis	Extensive clinical validation
			Requires vasodilation
iFR	≤ 0.9	Functionally significant epicardial stenosis	Functionally significant epicardial stenosis
			Vasodilation-Independent
HSR	0.8 mmHg × s/cm	Functionally significant epicardial stenosis	Requires doppler-pressure wire
			Convenient in the presence FFR/CFR discordances
HMR	> 2 mmHg × s/cm	Microvascular dysfunction	Requires doppler-pressure wire
IMR	> 25 mmHg × s	Microvascular dysfunction	Thermodilution method

CFR: Coronary flow reserve; FFR: Fractional flow reserve; iFR: Instantaneous wave free ratio; HSR: Hyperemic stenosis resistance index; HMR: Hyperemic microvascular resistance index; IMR: Index of microcirculatory resistance.