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CLINICAL RESEARCH: INVASIVE CARDIOLOGY

Direct Volumetric Blood Flow Measurement in Coronary Arteries by Thermodilution

Wilbert Aarnoudse, MD, PhD^_*,, Marcel van't Veer, MSc^_*,, Nico H.J. Pijls, MD, PhD^_*,,_*, Joost ter Woorst, MD, Steven Vercauteren, MD, Pim Tonino, MD^_*, Maartje Geven, MSc, Marcel Rutten, PhD, Eduard van Hagen, RN^_*, Bernard de Bruyne, MD, PhD and Frans van de Vosse, PhD

^_* Department of Cardiology, Catharina Hospital, Eindhoven, the Netherlands
Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands
Department of Cardiothoracic Surgery, Catharina Hospital, Eindhoven, the Netherlands
OLV Cardiovascular Center Aalst, Aalst, Belgium. Supported by grant EPG.54.54 of STW (Foundation of Applied Scientific Research) of the Dutch Ministry of Economic Affairs, by Radi Medical Systems, Uppsala, Sweden, and by the Friends of the Heart Foundation (Stichting Vrienden van het Hart), Eindhoven, the Netherlands. Drs. Aarnoudse and van't Veer contributed equally to this work

Manuscript received February 13, 2007; revised manuscript received August 21, 2007, accepted August 28, 2007.

^_* Reprint requests and correspondence: Dr. Nico H. J. Pijls, Catharina Hospital, Michelangelolaan 2, P.O. Box 1350, 5602 ZA Eindhoven, the Netherlands. (Email: nico.pijls{at}inter.nl.net).

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; R² = 0.72). Reproducibility was excellent (Q_thermo,1 = 0.96 x Q_thermo,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 (Q_thermo,1 = 1.0 Q_thermo,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.

Abbreviations and Acronyms   FFR = fractional flow reserve   FFRcor = coronary fractional flow reserve   FFRmyo = myocardial fractional flow reserve   Pa = aortic pressure (mm Hg) measured by the guiding catheter   Pd = distal coronary pressure (mm Hg) measured by the pressure wire   Pw = coronary wedge pressure (mm Hg) measured by the pressure wire during balloon occlusion of the coronary artery   Q = absolute coronary blood flow (ml/min) measured by the perivascular flow probe   Qb = theoretical value of absolute coronary blood flow during saline infusion   Qi = volumetric infusion rate of saline (ml/min)   Qthermo = volumetric coronary blood flow (ml/min) calculated by thermodilution   T = temperature of blood (°C) in the coronary artery at steady-state saline infusion   Tb = temperature of blood (°C) in the coronary artery before start of saline infusion   Ti = temperature of the infused saline (°C) when entering the coronary artery at the tip of the infusion catheter

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