The Microvascular Blind Spot
Coronary microvascular disease drives angina, heart failure, and poor outcomes despite normal epicardial arteries, yet invasive index of microcirculatory resistance (IMR) measurement remains the gold standard; however, it is hindered by procedural complexity and limited access. A new retrospective cohort study published in the Eurointervention introduces IMR-CT, a non-invasive index derived from routine coronary computed tomography angiography (CCTA), validated against invasive IMR (≥25 defining CMD) in 176 patients (216 vessels) evaluated between January 2022 and March 2024.
Strong Correlation: CT Meets Invasive Reality
IMR-CT demonstrated robust correlation with gold-standard invasive IMR, achieving r=0.71 (95% CI 0.62-0.76) at vessel level and r=0.72 (95% CI 0.64-0.78) at patient level (both p<0.001). Blinded evaluators calculated IMR-CT from CCTA performed within 30 days preceding invasive assessment, establishing computational feasibility within routine imaging workflows.
Diagnostic Performance: Filling the Gap
IMR-CT delivered solid diagnostic metrics against invasive IMR ≥25. At the vessel level, the accuracy is 81.9%, sensitivity is 80.8%, and specificity is 82.5%. The AUC is 0.82. At the patient level, the accuracy is 80.7%, sensitivity is 81.5%, and specificity is 80.2%. The AUC is 0.81.
These metrics position IMR-CT as clinically actionable, bridging the diagnostic chasm between symptom-driven invasive labs and widely available CCTA.
Transforming Non-Obstructive CAD
Among patients with CCTA stenosis <50%, coronary angiogram stenosis <50%, or FFR >0.8, traditional CMD assessment missed 35-39% of cases. IMR-CT slashed underdiagnosis rates to 4.5-5.9%, unmasking microvascular etiology in symptomatic patients dismissed as "non-obstructive."
For the Frontline Cardiologist
Next CCTA with unobstructed coronaries and persistent symptoms? Calculate IMRCT. AUC 0.81-0.82 accuracy transforms microvascular assessment to point-of-care reality. CMD underdiagnosis may be the past and symptomatic patients deserve the diagnosis that CCTA can now deliver.