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,)(1) = 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.