Impact of Procedural Differences on Bolus Thermodilution Method for Assessment of Coronary Microvascular Dysfunction

Background The thermodilution technique, employing bolus injections to measure coronary flow reserve (CFR) and the index of microcirculatory resistance (IMR), is widely used to assess coronary microvascular function. However, the potential influence of catheter size and operator differences on these measurements has not been systematically evaluated. Aims This study aimed to evaluate the feasibility and consistency of thermodilution‐based CMD assessment with respect to different catheter sizes and operators. Methods A total of 320 coronary arteries were assessed using a 0.014‐inch pressure–temperature sensor‐tipped guidewire. The data set included both angiographically normal vessels and those with varying degrees of stenosis. Results Four cases using 4 Fr catheters and data from three of seven operators (due to insufficient case numbers) were excluded. No statistically significant differences in CFR or IMR values were observed among the four operators. Similarly, no significant differences were found between experienced and less‐experienced operators (CFR: 1.90 vs. 1.80, p = 0.178; IMR: 19.00 vs. 20.50, p = 0.968). In contrast, CFR values varied significantly by catheter size (5 Fr: 2.20; 6 Fr: 1.80; 7 Fr: 1.50; 8 Fr: 1.70; p < 0.001), whereas IMR remained unaffected. When catheter sizes were dichotomized (small: 5–6 Fr; large: 7–8 Fr), CFR was significantly higher in the small‐size group (1.95 vs. 1.65, p = 0.003), while IMR showed no significant difference (20.00 vs. 20.00, p = 0.239). Conclusions While the selection of larger catheter sizes may affect CFR with thermodilution, common sizes and operator techniques show consistent results in practice.