Coronary physiology assessment in the catheterization laboratory

Table 1 Substances used in the catheterization laboratory for coronary vascular function assessment

Substance	Doses	Site of action	Endothelium response	Effect
Adenosine	Iv: 140 μg/kg per minute Ic: 20-150 μg bolus	Microvascular	Independent	Direct vasodilation
Acetylcholine	Ic: 10-6 M/10-5 M/ 10-4 M	Micro and macrovascular	Dependent	Vasodilation if normal endothelial function; vasoconstriction if endothelial dysfunction
Nitroglycerin	Ic: 200 μg bolus	Macrovascular	Independent	Vasodilation
Nitroprusside	Ic 0.3-0.9 μg/kg bolus	Micro and macrovascular	Independent	Vasodilation
Papaverine	Ic: 8-20 mg bolus	Micro and macrovascular	Independent	Enzyme Phosphodiesterase inhibition Vasodilation
Regadenoson	Iv: 400 μg bolus	Microvascular	Independent	Adenosine receptor agonist vasodilation

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.