A Novel Computational Approach to Assess Microcirculatory Resistance for assessing microcirculatory resistance in patients with non-obstructed vessels

Background An intracoronary wire equipped with a transducer and at least 3 to 4 ml of room-temperature saline injected into the coronary artery during prolonged congestion are often used to assess the index of microcirculatory resistance (IMR). This is a time-consuming and expensive procedure. Methods With the invasive wire-based IMR serving as the reference standard, this prospective, single-center, randomized study aims to evaluate the diagnostic performance of the novel single-view, pressure-wire- and adenosine-free angiographic microvascular resistance (AMR) index in patients with suspected myocardial ischemia and nonobstructive coronary arteries. AMR was blindedly and independently computed from the diagnostic coronary angiography. An independent core laboratory determined AMR on-site in real-time and compared it blindly to wire-based IMR, interpreting wire-based IMR of ≥25 units as abnormal coronary microcirculatory resistance. The main outcome, measured against wire-based IMR as a reference, was AMR's diagnostic accuracy. Using pressure wire-based IMR, 200 patients (200 vessels) were studied. The criteria for microvascular dysfunction (CMD) was IMR ≥ 25. AMR was blindedly and independently computed from the diagnostic coronary angiography. Results The mean AMR was 2.44±0.68 and showed good correlation (r = 0.6672, p < 0.001) with IMR. A least-squares fit shows a relationship: AMR=1.8+0.024 IMR (regression coefficient 95% CI: 0.011-0.037, P=0.001). According to microcirculatory status, Two groups were divided: low IMR (<25 U, non-CMD group) and high IMR (≥25 U, CMD group). AMR values were found to be significantly higher in the CMD group than in the non-CMD group (2.78±0.68 vs 2.03±0.40,P=0.004).The AUC for the diagnosis of CMD by ROC curve analysis of AMR was 0.889 (95% CI: 0.707-1.0). Conclusion AMR derived from angiographic views is a viable computational alternative to pressure line-based IMR, with good diagnostic accuracy in the assessment of CMD.