Coronary thermodilution to assess flow reserve: experimental validation

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.

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 (r>0.95) was found between absolute flow and 1/T(mn) 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/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) (r=0.76; SEE=0.24; P<0.001).

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.