Objectives: Recently, a combined 0.014 pressure/temperature sensor-mounted guide wire has been developed to simultaneously measure fractional flow reserve and coronary flow reserve (CFR) by thermodilution (CFR-thermo). The accuracy of CFR-thermo was compared with CFR obtained by flow rate (CFR-flow) in experimental models.
Methods: Using an experimental model made from a straight-rigid tube (4 mm diameter) filled with 36 degrees C water, CFR-thermo and CFR-flow were measured under different conditions of sensor position and injected water temperature (0-40 degrees C). A side branch (2 mm diameter) was then placed at 4, 6, 8 and 10 cm from the injected site just proximal to the stenosis. The degree of stenosis ranged from 0 to 75% (0%, 25%, 50%, 75%). CFR-thermo and CFR-flow were calculated from the inverse ratio of the mean transit time and the flow ratio during high flow to low flow rates.
Results: Under the conditions without the side branch, there were good correlations between CFR-thermo and CFR-flow if the temperature of the injected water was under 28 degrees C and the sensor was not placed within 4 cm from the injection site. With the side branch, CFR-thermo was smaller than CFR-flow although there were good correlations between CFR-thermo and CFR-flow. The value of CFR-thermo increased with more distal positions of the side branch to the injected site.
Conclusions: Temperature of the injected water, and the position of the sensor, the side branch and the stenotic lesion may influence measurements of CFR-thermo. These effects should be considered when CFR is measured by the thermodilution method.