Prognostic value of coronary Angiographic Microvascular Resistance Index in patients with myocardial infarction with nonobstructive coronary arteries

Background and objective Microcirculatory dysfunction is a known cause of myocardial infarction with nonobstructive coronary arteries (MINOCA). Angiography-derived microcirculatory resistance (AMR), a wire-free and adenosine-free index, offers a potential method for early assessment of microvascular function in these patients at the time of angiography. This study aimed to evaluate the prognostic impact of the Angiographic Microvascular Resistance (AMR) Index in patients with MINOCA. Methods A retrospective study was conducted on patients with acute MINOCA who underwent coronary angiography between January 2017 and March 2024. AMR was computed from coronary angiography. The primary endpoint of our investigation was the occurrence of major adverse cardiovascular events (MACE), specifically defined as encompassing cardiovascular death, stroke, heart failure, nonfatal myocardial infarction, and angina rehospitalization. Kaplan–Meier, Cox regression, and receiver-operating characteristic (ROC) analyses were performed. The best cutoff of AMR was derived from ROC analysis based on the MACE prediction. Results Overall, 205 MINOCA patients were included in the final analysis of this study. During a median follow-up of 38 months, a total of 63 (30.7%) patients developed MACE. The area under the curve for AMR to predict MACE was 0.702 95% confidence interval (CI) 0.617–0.786, with an optimal cutoff value of 35 mmHg s/dm. AMR, whether as a continuous per 1SD increase in the AMR Index, hazard ratio, 1.72 (95% CI 1.36–2.17); P 35; hazard ratio, 3.32 (95% CI 1.99–5.52); P < 0.001 variable, was independently associated with MACE after adjusting for traditional risk factors. Incorporating AMR into the Thrombolysis In Myocardial Infarction (TIMI) score resulted in a significant improvement in discrimination for MACE net reclassification improvement (NRI) 0.211; P = 0.006. Conclusion In conclusion, increased AMR was independently associated with poor prognosis following MINOCA. These findings suggest that AMR may play a potential role in the cardiovascular risk stratification of the MINOCA population.