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 (Qthermo) 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 (Qthermo = 0.73 Q + 42 ml/min; R2 = 0.72). Reproducibility was excellent (Qthermo,1 = 0.96 × Qthermo,2 + 3 ml/min; R2 = 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 (R2 = 0.84); reproducibility of the measurements was excellent (Qthermo,1 = 1.0 Qthermo,2 + 0.9 ml/min, R2 = 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. © 2007 American College of Cardiology Foundation.
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