Invasive Measures of Myocardial Perfusion and Ischemia
Section snippets
Definition
Fractional flow reserve (FFR) has been defined19 as the ratio of maximal myocardial blood flow in the presence of the stenosis divided by the theoretically normal maximal myocardial blood flow (i.e. in the absence of the stenosis). Stated another way, FFR informs the operator to what extent the presence of the stenosis limits the maximum achievable flow and, thus, to what extent the restoration of the epicardial conductance will increase myocardial perfusion. FFR can uniquely quantify
Definition
Coronary flow reserve (CFR) has been introduced by K Lance Gould2 who pioneered the era of applied coronary physiology or āphysiological thinkingā about CAD. CFR is defined as the extent to which myocardial or coronary flow can increase above its baseline value as obtained during maximal pharmacological hyperemia. CFR quantifies the ratio of stress to rest flow in the diseased vessel. Functional assessment of ischemia using perfusion imaging produces global myocardial flow misdistribution data
Definition
Hyperemic stenosis resistance (HSR) is an index of the resistance to flow opposed by the epicardial narrowing.41 It has been proposed by the groups of Spaan and Piek. Theoretically it should provide the most accurate description of the functional consequences of a given stenosis as it takes into account both the pressure gradient and the flow (velocity).
Calculation
HSR is the ratio of the transstenotic pressure gradient divided by the coronary blood flow velocity under conditions of maximal hyperemia. The
Definition
The index of microvascular resistance (IMR) was introduced by Fearon44 as the first means to quantify the resistance of the coronary microvasculature. IMR measures the resistance to myocardial flow specifically related to the microvascular compartment.
Calculation
IMR is calculated from the ratio of distal coronary pressure, Pd, and the thermodilution-derived mean transit time during maximal micro- and macrovascular vasodilation, Tmn. The latter can be obtained by a bolus injection of 3ā4Ā mL of saline at
Definition
The instantaneous wave-free ratio (iFR) was introduced by Sen and Davies.50 It can be defined as the ratio of resting distal coronary pressure to aortic pressure, during diastole, when resistance is allegedly ānaturallyā constant and minimized.
In contrast to all other indices, iFR does not aim at measuring any physical characteristics (flow, pressure or resistance) of the coronary circulation.
Calculation
iFR is calculated as the mean pressure distal to the stenosis during the diastolic wave-free period (Pd
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A new reduced-order model to assess the true fractional flow reserve of a left main coronary artery stenosis with downstream lesions and collateral circulations: an inĀ vitro study
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2016, Journal of the American College of CardiologyFunctional Coronary Artery Assessment: aĀ Systematic Literature Review
2022, Wiener Klinische WochenschriftPathophysiologic Basis and Diagnostic Approaches for Ischemia With Non-obstructive Coronary Arteries: A Literature Review
2022, Frontiers in Cardiovascular Medicine
Disclosure information: Dr. Adjedj is supported by a research grant from the FƩdƩration Francaise de Cardiologie. Dr. Toth has no conflicts of interest. Dr. De Bruyne reports that his institution receives grant support and consulting fees on his behalf from St. Jude Medical.