Coronary thermodilution to assess flow reserve - Experimental validation

Background-Fractional flow reserve (FFR) and coronary flow reserve (CFR) ar e indices of coronary stenosis severity that provide the clinician with com plementary information on the contribution of epicardial arteries and micro circulation to total resistance to myocardial blood flow. At present, FFR a nd CFR can only be obtained by 2 separate guidewires. The present study tes ted 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 t he inverse mean transit time (1/T-mn) of a thermodilution curve obtained af ter a bolus injection of 3 mL of saline at room temperature. A very close c orrelation (r >0.95) was found between absolute flow and 1/T-mn when the se nsor was placed greater than or equal to6 cm from the injection site. In 6 chronically instrumented dogs (60 stenoses; FFR from 0.19 to 0.98), a signi ficant linear relation was found between flow velocity and 1/T-mn. A signif icant correlation was found between CFRDoppler, which was calculated from t he ratio of hyperemic to resting flow velocities, and CFRthermo, which was calculated from the ratio of resting to hyperemic T-mn (r=0.76; SEE=0.24; P <0.001). Conclusion-The present findings demonstrate the validity of the thermodilut ion principle to assess CFR. Because the pressure-temperature sensor was mo unted in a commercially available angioplasty guidewire, this technique per mits simultaneous measurements of CFR and FFR.