Microvascular Resistance Reserve assessed by bolus and continuous thermodilution

Abstract

Abstract Aim The main limitation of Coronary flow reserve (CFR) as an index to assess coronary microvascular function, is that it is influenced by epicardial resistance. Microvascular Resistance Reserve (MRR) has been recently introduced as a metric that is truly specific for the coronary microcirculation. MRR can, in principle, be derived from any tool that measure flow and pressure. The aim of the present study was to compare CFR and MRR as derived by bolus (CFRbolus and MRRbolus, respectively) and continuous thermodilution (CFRcont and MRRcont, respectively). Methods and Results A total of 175 patients were studied. Bolus and continuous thermodilution measurements were performed in the LAD in all patients. The MRR was derived as a function of the coronary flow reserve (CFR) divided by the fractional flow reserve (FFR) and corrected for driving pressures. Coefficient of variation was calculated to assess the precision of both methods. Mean CFRbolus was higher than the corresponding value of CFRcont (3.47±1.42 and 2.67±0.81, respectively, p<0.001, mean bias 0.80). Also mean MRRbolus was higher than the corresponding value of MRRcont (4.40±1.99 vs 3.22±1.02, respectively p<0.001, mean bias 1.2) The correlation between CFR and MRR values obtained by both approaches was weak (R= 0.28 (0.14 to 0.41) for CFR; R=0.26 (0.16 to 0.39) for MRR; p<0.001 for both). Continuous thermodilution had a smaller dispersion of data for both CFR (CoV= 30.2% vs 46.6% respectively, p<0.001) and MRR (CoV= 31.7 % vs 45.2% vs, respectively, p<0.001). Conclusion Bolus thermodilution significantly overestimates continuous thermodilution-derived CFR and MRR and shows a larger scatter of the data. Therefore, bolus thermodilution seems a less appropriate method to assess microvascular function than is continuous thermodilution.