Coronary thermodilution to assess flow reserve : experimental validation

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/Tmn) of a thermodilution curve obtained after a bolus injection of 3 mL of saline at room temperature. A very close correlation (r>0.95) was found between absolute flow and 1/Tmn when the sensor was placed 6 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/Tmn. A significant correlation was found between CFRDoppler, which was calculated from the ratio of hyperemic to resting flow velocities, and CFRthermo, which was calculated from the ratio of resting to hyperemic Tmn (r=0.76; SEE=0.24; P