Comparison of Coronary Thermodilution and Doppler Velocity for Assessing Coronary Flow Reserve

Background - Thermodilution coronary flow reserve (CFR_thermo) is a new technique for invasively measuring coronary flow reserve (CFR) with a coronary pressure wire and is based on the ability of the pressure transducer to also measure temperature changes. Whether CFR_thermo correlates well enough with absolute flow-derived CFR (CFR_flow) to replace Doppler wire-derived CFR (CFRDoppler) remains unclear. Methods and Results - In an open-chest pig model, CFR_thermo was measured in the left anterior descending (LAD) artery and compared with CFR_Doppler and CFR _flow, measured with an external flow probe placed around the LAD. In 9 pigs, CFR was measured simultaneously by all 3 means in the normal LAD and after creation of an epicardial LAD stenosis. To determine the added effect of microvascular disease, measurements of flow reserve were also performed after disruption of the coronary microcirculation with embolized microspheres. Intracoronary papaverine (20 mg) was used to induce hyperemia. In a total of 61 paired measurements, CFR_thermo correlated strongly with the reference standard CFR_flow (r=0.85, P<0.001). CFR _Doppler correlated less well with CFR_flow (r=0.72, P<0.001). Bland-Altman analysis showed a closer agreement between CFR _thermo and CFR_flow. Conclusion - CFR_thermo correlates better with CFR_flow than does CFR_Doppler.