Background-Guide wire-based simultaneous measurement of fractional flow reserve (FFR) and coronary flow reserve (CFR) is important to understand microvascular disease of the heart. The aim of this study was to investigate the feasibility of simultaneous measurement of FFR and CFR by one pressure-temperature sensor-tipped guide wire with the use of coronary thermodilution and to compare CFR by thermodilution (CFR thermo ) with simultaneously measured Doppler CFR (CFR Doppl ). Methods and Results-In 103 coronary arteries in 50 patients, a pressure-temperature sensor-tipped 0.014-inch floppy guide wire and a 0.014-inch Doppler guide wire were introduced. Both normal vessels and a wide range of stenotic vessels were included. With 3 mL of saline at room temperature used as an indicator, by hand-injection, thermodilution curves in the coronary artery were obtained in triplicate, both at baseline and at intravenous adenosine-induced maximum hyperemia. After adequate curve-fitting, CFR thermo was calculated from the ratio of inverse mean transit times and compared with CFR Doppl calculated by velocities at hyperemia and baseline. Adequate sets of thermodilution curves and corresponding CFR thermo could be obtained in 87% of the arteries versus 91% for Doppler CFR and 100% for FFR. CFR thermo correlated fairly well to CFR Doppl (CFR thermo ϭ0.84 CFR Doppl ϩ0.17; rϭ0.80; PϽ0.001), although individual differences of Ͼ20% between both indexes were seen in a quarter of all arteries. Conclusions-This study shows the feasibility of simultaneous measurement of FFR (by coronary pressure) and CFR (by coronary thermodilution) in humans by one single guide wire in a practical and straightforward way and will facilitate assessment of microvascular disease.

Background-Whether minimal microvascular resistance of the myocardium is affected by the presence of an epicardial stenosis is controversial. Recently, an index of microcirculatory resistance (IMR) was developed that is based on combined measurements of distal coronary pressure and thermodilution-derived mean transit time. In normal coronary arteries, IMR correlates well with true microvascular resistance. However, to be applicable in the case of an epicardial stenosis, IMR should account for collateral flow. We investigated the feasibility of determining IMR in humans and tested the hypothesis that microvascular resistance is independent of epicardial stenosis. Methods and Results-Thirty patients scheduled for percutaneous coronary intervention were studied. The stenosis was stented with a pressure guidewire, and coronary wedge pressure (P w ) was measured during balloon occlusion. After successful stenting, a short compliant balloon with a diameter 1.0 mm smaller than the stent was placed in the stented segment and inflated with increasing pressures, creating a 10%, 50%, and 75% area stenosis. At each of the 3 degrees of stenosis, fractional flow reserve (FFR) and IMR were measured at steady-state maximum hyperemia induced by intravenous adenosine. A total of 90 measurements were performed in 30 patients. When uncorrected for P w , an apparent increase in microvascular resistance was observed with increasing stenosis severity (IMRϭ24, 27, and 37 U for the 3 different degrees of stenosis; PϽ0.001). In contrast, when P w is appropriately accounted for, microvascular resistance did not change with stenosis severity (IMRϭ22, 23, and 23 U, respectively; Pϭ0.28). Conclusions-Minimal microvascular resistance does not change with epicardial stenosis severity, and IMR is a specific index of microvascular resistance when collateral flow is properly taken into account.

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