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.