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-Fractional flow reserve (FFR) and coronary flow reserve (CFR) are indices of coronary stenosis severity that provide the clinician with complementary information on the contribution of epicardial arteries and microcirculation to total resistance to myocardial blood flow. At present, FFR and CFR can only be obtained by 2 separate guidewires. The present study tested the validity of the thermodilution principle in assessing CFR with one pressure-temperature sensor-tipped guidewire. Methods and Results-In an in vitro model, absolute flow was compared with the inverse mean transit time (1/T mn ) of a thermodilution curve obtained after a bolus injection of 3 mL of saline at room temperature. A very close correlation (rϾ0.95) was found between absolute flow and 1/T mn when the sensor was placed Ն6 cm from the injection site. In 6 chronically instrumented dogs (60 stenoses; FFR from 0.19 to 0.98), a significant linear relation was found between flow velocity and 1/T mn . A significant correlation was found between CFR Doppler , which was calculated from the ratio of hyperemic to resting flow velocities, and CFR thermo , which was calculated from the ratio of resting to hyperemic T mn (rϭ0.76; SEEϭ0.24; PϽ0.001). Conclusion-The present findings demonstrate the validity of the thermodilution principle to assess CFR. Because the pressure-temperature sensor was mounted in a commercially available angioplasty guidewire, this technique permits simultaneous measurements of CFR and FFR.

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