Coronary microvascular dysfunction assessed by continuous intracoronary thermodilution: A comparative study with index of microvascular resistance

This study aimed to assess the correlation between the standard of care, the index of microvascular resistance (IMR) versus the novel microvascular resistance (Rmicro) and to determine the pathologic cut-off value in a selected population with suspected coronary microvascular dysfunction (CMD). One-hundred and twenty patients with high clinical suspicion of CMD due to ischemic symptoms in the absence of significant epicardial coronary lesions were prospectively included. Following a standardized systematic protocol, coronary flow reserve, IMR, fractional flow reserve, Q and Rmicro were measured in the left anterior descending coronary artery using a temperature/pressure sensor-tipped guidewire and a dedicated infusion catheter. There was a high prevalence of CMD with 50 (42%) patients showing an IMR ≥ 25. Median IMR was 23 [IQR: 14–34] and median Rmicro was 464 Woods Units (WU) [IQR: 354–636WU]. ROC analyses identified 500 WU as the optimal Rmicro cut-off to identify patients with an IMR ≥ 25, with an area under the ROC curve (C statistic) of 0.83 (95% CI: 0.74 to 0.89, p 500 WU predicts the presence of coronary microvascular dysfunction.