Repeatability and Correlation of Coronary Physiology Indices Measured With Bolus and Continuous Thermodilution

BACKGROUND: Previous studies have shown weak agreement between coronary physiology indices derived from continuous and bolus thermodilution, and suggested greater variability with bolus thermodilution measurements. This study aimed to evaluate the repeatability and correlation of continuous and bolus thermodilution–derived physiology indices in cardiac transplant recipients. METHODS: Paired fractional flow reserve (FFR), coronary flow reserve (CFR), index of microcirculatory resistance (IMR), absolute hyperemic resistance (R Hyp ), and microvascular resistance reserve (MRR) using continuous and bolus thermodilution were performed in consecutive cardiac transplant recipients. RESULTS: In 20 patients, IMR was more repeatable than CFR and MRR derived from either continuous thermodilution (intraclass correlation coefficient, 0.95 versus 0.70 and 0.59; P =0.004 and P =0.002, respectively) or bolus thermodilution (intraclass correlation coefficient, 0.95 versus 0.20 and 0.33; P <0.001 and P =0.002, respectively), and similarly repeatable compared with R Hyp (intraclass correlation coefficient, 0.95 versus 0.87; P =0.188). FFR by continuous thermodilution correlated with standard FFR measurements ( R =0.89, P <0.001) but were significantly lower in value (0.87±0.05 versus 0.89±0.05; P =0.004). CFR and MRR measurements using continuous thermodilution did not correlate with measurements using bolus thermodilution ( R =0.33, P =0.170; R =0.34, P =0.155, respectively) and were significantly lower in value (2.9±1.0 versus 3.7±0.8, P =0.003; 3.4±1.1 versus 4.8±1.3, P <0.001, respectively). IMR and R Hyp did not correlate ( R =0.28, P =0.226). CONCLUSIONS: In cardiac transplant recipients, IMR had superior repeatability compared with CFR and MRR derived from either bolus or continuous thermodilution, and was equally repeatable compared with R Hyp . FFR, CFR, and MRR values obtained from continuous thermodilution were systematically lower compared with their counterparts obtained from bolus thermodilution.