Invasive Assessment of the Coronary Microcirculation

Abstract

Background-A simple, reproducible invasive method for assessing the coronary microcirculation is lacking. A novel index of microcirculatory resistance (IMR) has been shown in animals to correlate with true microvascular resistance and, unlike coronary flow reserve (CFR), to be independent of the epicardial artery. We sought to compare the reproducibility and hemodynamic dependence of IMR with CFR in humans. Methods and Results-Using a pressure-temperature sensor-tipped coronary wire, thermodilution-derived CFR and IMR were measured, along with fractional flow reserve (FFR), in 15 coronary arteries (15 patients) under the following hemodynamic conditions: (1) twice at baseline; (2) during right ventricular pacing at 110 bpm; (3) during intravenous infusion of nitroprusside; and (4) during intravenous dobutamine infusion. Mean CFR did not change during baseline measurements or during nitroprusside infusion but decreased during pacing (from 3.1Ϯ1.1 at baseline to 2.3Ϯ1.2 during pacing, PϽ0.05) and during dobutamine infusion (from 3.0Ϯ1.0 to 1.7Ϯ0.6 with dobutamine, PϽ0.0001). By comparison, mean values for IMR and FFR remained similar throughout all hemodynamic conditions. The mean coefficient of variation between 2 baseline measurements was significantly lower for IMR (6.9Ϯ6.5%) and FFR (1.6Ϯ1.6%) than for CFR (18.6Ϯ9.6%; PϽ0.01). Mean correlation between baseline measurements and each hemodynamic intervention was superior for IMR (rϭ0.90Ϯ0.05) and FFR (rϭ0.86Ϯ0.12) compared with CFR (rϭ0.70Ϯ0.05; PϽ0.05). Conclusions-Compared with CFR, IMR provides a more reproducible assessment of the microcirculation, which is independent of hemodynamic perturbations. Simultaneous measurement of FFR and IMR may provide a comprehensive and specific assessment of coronary physiology at both epicardial and microvascular levels, respectively. (Circulation.

Index of Microcirculatory Resistance at the Time of Primary Percutaneous Coronary Intervention Predicts Early Cardiac Complications: Insights From the OxAMI (Oxford Study in Acute Myocardial Infarction) Cohort

“…IMR is an objective and specific index to assess the microcirculation, which can easily and safely be measured at the time of PPCI 7, 8. The strength of IMR is not only in predicting myocardial recovery, final infarct size, and left ventricular ejection fraction,9, 10, 11 which are related to subsequent heart failure, but also in predicting the presence of microvascular dysfunction,10, 11 which is itself associated with early life‐threatening ventricular arrhythmias 29…”

“…This maybe explained by the influence of hemodynamic factors, such as heart rate and blood pressure on CFR,8 which have less impact on IMR. Furthermore, CFR is unable to distinguish between the contribution of epicardial and microvascular beds to total resistance 7…”

“…The thermodilution‐derived index of microcirculatory resistance (IMR) is a specific, quantitative, and reproducible measure of microvascular function,7, 8 which predicts infarct size and left ventricular ejection fraction after an acute myocardial infarction 9, 10, 11. Moreover, an IMR value >40, measured at the time of PPCI, is associated with adverse long‐term outcomes in terms of death and rehospitalization for heart failure 12.…”

Impact of Smoking on Coronary Microcirculatory Resistance in Patients With Coronary Artery Disease

“…Coronary physiology measurements: Coronary physiology measurements were performed for all intermediate stenoses, as described previously. 8,[14][15][16][17][18][19] All patients received an intravenous bolus injection of 5,000 IU of heparin and intracoronary isosorbide dinitrate (1-2 mg) before angiography. A coronary 0.014-inch pressure-temperature sensor guidewire (Certus, St. Jude Medical, St. Paul, MN, USA) threaded through 5 Fr diagnostic catheters was used for measurements after a diagnostic coronary angiogram (CAG) (Figure 1).…”

Assessing the Coronary Microcirculation in Patients After Primary Percutaneous Coronary Intervention

“…IMR corresponds with the extent of coronary microvasculature disruption in humans,6 and is stable and reproducible in the presence of varying hemodynamic conditions 7. In earlier studies, IMR measured immediately after primary PCI correlated with myocardial infarct size as measured by peak creatine kinase, whereas other less quantitative or specific measures of the microcirculation (including TIMI myocardial perfusion grade, TIMI frame count, coronary flow reserve, and ST‐segment resolution) did not 8.…”