Direct volumetric blood flow measurement in coronary arteries by thermodilution

Objectives This study sought to validate a new method for direct volumetric blood flow measurement in coronary arteries in animals and in conscious humans during cardiac catheterization. Background Direct volumetric measurement of blood flow in selective coronary arteries would be useful for studying the coronary circulation. Methods Based on the principle of thermodilution with continuous low-rate infusion of saline at room temperature, we designed an instrumental setup for direct flow measurement during cardiac catheterization. A 2.8-F infusion catheter and a standard 0.014-inch sensor-tipped pressure/temperature guidewire were used to calculate absolute flow (Q(thermo)) in a coronary artery from the infusion rate of saline, temperature of the saline at the tip of the infusion catheter, and distal blood temperature during infusion. The method was tested over a wide range of flow rates in 5 chronically instrumented dogs and in 35 patients referred for physiological assessment of a coronary stenosis or for percutaneous coronary intervention. Results Thermodilution-derived flow corresponded well with true flow (Q) in all dogs (Q(thermo) = 0.73 Q + 42 ml/min; R-2 = 0.72). Reproducibility was excellent (Q(thermo) = 0.96 X Q(thermo,2) + 3 ml/min; R-2 = 0.89). The measurements were independent of infusion rate and sensor position as predicted by theory. In the humans, a good agreement was found between increase of thermodilution-derived volumetric blood flow after percutaneous coronary intervention and increase of fractional flow reserve (R-2 = 0.84); reproducibility of the measurements was excellent (Q(thermo,1) = 1-0 Q(thermo,2) + 0.9 ml/min, R-2 = 0.97), and the measurements were independent of infusion rate and sensor position. Conclusions Using a suitable infusion catheter and a 0.014-inch sensor-tipped guidewire for measurement of coronary pressure and temperature, volumetric blood flow can be directly measured in selective coronary arteries during cardiac catheterization.