Simplification of continuous intracoronary thermodilution

Background: Continuous intracoronary thermodilution with saline allows for the accurate measurement of volumetric blood flow (Q) and absolute microvascular resistance (Rμ). However, this requires repositioning of the temperature sensor by the operator to measure the entry temperature of the saline infusate, denoted as Ti.

Aims: We evaluated whether Ti could be predicted based on known parameters without compromising the accuracy of calculated Q. This would significantly simplify the technique and render it completely operator independent.

Methods: In a derivation cohort of 371 patients with Q measured both at rest and during hyperaemia, multivariate linear regression was used to derive an equation for the prediction of Ti. Agreement between standard Q (calculated with measured Ti) and simplified Q (calculated with predicted Ti) was assessed in a validation cohort of 120 patients that underwent repeat Q measurements. The accuracy of simplified Q was assessed in a second validation cohort of 23 patients with [15O]H2O positron emission tomography (PET)-derived Q measurements.

Results: Simplified Q exhibited strong agreement with standard Q (r=0.94, confidence interval [CI]: 0.93-0.95; intraclass correlation coefficient [ICC] 0.94, CI: 0.92-0.95; both p<0.001). Simplified Q exhibited excellent agreement with PET-derived Q (r=0.86, CI: 0.75-0.92; ICC=0.84, CI: 0.72-0.91; both p<0.001). Compared with standard Q, there were no statistically significant differences between correlation coefficients (p=0.29) or standard deviations of absolute differences with PET-derived Q (p=0.85).

Conclusions: Predicting Ti resulted in an excellent agreement with measured Ti for the assessment of coronary blood flow. It significantly simplifies continuous intracoronary thermodilution and renders absolute coronary flow measurements completely operator independent.