Non-invasive assessment of microcirculatory resistance by coronary computed tomography angiography.

BACKGROUND: Despite its high prevalence and major prognostic implications, coronary microvascular disease (CMD) is frequently underdiagnosed owing to the complexity and invasiveness of current diagnostic procedures. AIMS: This study aimed to introduce and validate the usefulness of a non-invasive index of microcirculatory resistance (IMR) derived from coronary computed tomography angiography (CCTA), called IMRCT, for accurate diagnosis of CMD. METHODS: This retrospective cohort study comprised consecutive patients referred for invasive coronary functional assessments who underwent CCTA within the 30 days preceding an invasive evaluation between January 2022 and March 2024. IMRCT was calculated by blinded evaluators and compared against invasively determined IMR, with IMR values ≥25 indicating CMD, to assess its diagnostic performance. RESULTS: A total of 176 patients (216 vessels) were included in the analysis. IMRCT showed good correlation with invasively measured IMR, both at the vessel level (r=0.71, 95% confidence interval [CI]: 0.62-0.76; p<0.001) and the patient level (r=0.72, 95% CI: 0.64-0.78; p<0.001). At the vessel level, diagnostic accuracy, sensitivity, specificity, and area under the curve were 81.9%, 80.8%, 82.5%, and 0.82, respectively; corresponding values at the patient level were 80.7%, 81.5%, 80.2%, and 0.81. In patients with non-obstructive coronary artery disease defined by CCTA stenosis <50%, coronary angiogram stenosis <50%, or fractional flow reserve>0.8, IMRCT reduced underdiagnosis rates from 38.8%, 35.3%, and 36.3% to 4.5%, 5.9%, and 5.6%, respectively. CONCLUSIONS: IMRCT serves as a valuable complement to current diagnostic approaches, addressing their limitations and offering a promising alternative for the diagnosis of CMD, with the potential to significantly reduce misdiagnosis rates.