Thermodilution-derived volumetric resting coronary blood flow measurement in humans

Abstract

Background: Quantification of microvascular function requires the measurement of flow and resistance at rest and during hyperaemia. Continuous intracoronary thermodilution accurately measures coronary flow during hyperaemia.

Aims: The aim of this study was to investigate whether continuous coronary thermodilution using lower infusion rates also enables volumetric coronary blood flow measurements (in mL/min) at rest.

Methods: In 59 patients (88 arteries), the ratio of distal to proximal coronary pressure (Pd/Pa), as well as absolute blood flow (in mL/min) by continuous thermodilution, was recorded using a pressure/temperature guidewire. Saline was infused at rates of 10 and 20 mL/min. In 27 arteries, Doppler average peak velocity (APV) was measured simultaneously. Pd/Pa, APV, thermodilution-derived coronary flow reserve (CFRthermo) and coronary flow velocity reserve (CFVR) were assessed. In 10 arteries, simultaneous recordings were obtained at saline infusion rates of 6, 8, 10 and 20 mL/min.

Results: Compared to baseline, saline infusion at 10 mL/min did not change Pd/Pa (0.95±0.05 versus 0.94±0.05, p=0.49) or APV (22±8 versus 23±8 cm/s, p=0.60); conversely, an infusion rate of 20 mL/min induced a decrease in Pd/Pa and an increase in APV. Stable thermodilution tracings were obtained during saline infusion at 8 and 10 mL/min, but not at 6 mL/min. Mean values of CFRthermo and CFVR were similar (2.78±0.91 versus 2.76±1.06, p=0.935) and their individual values correlated closely (r=0.89, 95% CI: 0.78-0.95, p<0.001).

Conclusions: In addition to hyperaemic flow, continuous thermodilution can quantify absolute resting coronary blood flow; therefore, it can be used to calculate coronary flow reserve and microvascular resistance reserve.

Conflict of interest statement

C. Collet reports receiving research grants from Biosensors, HeartFlow Inc., Shockwave Medical, Pie Medical, Siemens, Medis Medical Imaging and Abbott Vascular, and consultancy fees from Opsens, Boston Scientific, Medyria, HeartFlow Inc., and Philips/Volcano. B. De Bruyne has received grants from Abbott Vascular, Boston Scientific and Biotronik, institutional consulting fees from Abbott and Boston Scientific, and is a shareholder in Philips, Siemens, GE, Bayer, HeartFlow, Edwards Lifesciences, and Ceyliad. S. Fournier declares speaker fees from Bayer, Amgen, and Biotronik, and consulting fees (advisory boards) from Bayer, and CathWorks. M. van ’t Veer declares speaker fees from Abbott. N. Pijls declares institutional research grants from Abbott and Hexacath, consultancy for Abbott, Opsens and General Electric, and minor equity in Philips, ASML, HeartFlow and GE. The other authors have no conflicts of interest to declare.

Figures

Figure 1

Example of simultaneous tracings of phasic and mean central aortic pressure, distal coronary pressure, average peak velocity and thermodilution during the infusion of 10 mL/min and of 20 mL/min of saline in the LAD of a 77-year-old male patient with mild wall irregularities. A) After the start and during the next 70 s of the infusion of saline at 10 mL/min through the RayFlow catheter located in the proximal LAD, no changes in distal coronary pressure, in Pd/Pa, or in APV were observed (reflecting a resting state). The slight oscillations in flow velocities (***) are caused by the pullback of the pressure/temperature wire. B) In contrast, after the start and during the next 70 s of the infusion of saline at 20 mL/min through the RayFlow catheter located in the proximal LAD, a decrease in Pd, a decrease in Pd/Pa, and an increase in APV were observed. After cessation of the intracoronary saline infusion, these indices returned to their baseline level. On the right-hand side, the CoroFlow software displays instantaneously all relevant parameters, including infusion rate, flow and resistance. APV: average peak velocity; LAD: left anterior descending coronary artery; Pa: aortic pressure; Pd: distal coronary pressure

Figure 2

Individual values, mean and SD of Pd/Pa (A) and APV (B) observed at baseline and during saline infusion at 10 and 20 mL/min. APV: average peak velocity; Pa: aortic pressure; Pd: distal coronary pressure

Figure 3

Correlation (A) and agreement (B) between thermodilution-derived coronary flow reserve (CFRthermo) and coronary flow velocity reserve (CFVR).

Figure 4

Individual values of of Pd/Pa and APV in the “dose-finding study” (6, 8, 10, 20 mL/min). ns: p ≥0.05. * p<0.05. ** p<0.001. APV: average peak velocity; Pa: aortic pressure; Pd: distal coronary pressure