Single-view angiographic microcirculatory resistance index after primary PCI: the EARLY-MYO-AMR study.

Background: Coronary microvascular dysfunction (CMD) leads to inadequate myocardial perfusion in patients with ST-segment elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PPCI). The index of microcirculatory resistance (IMR) is an intraoperative diagnostic tool for CMD. However, its widespread application is hindered by the requirement for pressure wires and hyperaemic agents. The angiographic microcirculatory resistance (AMR) index is concise, convenient, accurate, and serves as a pressure wire-free alternative to the IMR.

Aims: This study aimed to demonstrate the ability of AMR to detect CMD in patients with STEMI undergoing PPCI therapy and to assess its predictive value for long-term prognosis.

Methods: The EARLY-MYO-AMR trial comprised two cohorts. The derivation cohort included 495 patients with STEMI who underwent PPCI within 12 h and cardiac magnetic resonance (CMR) within 14 days of symptom onset. The optimal AMR cutoff value for diagnosing CMD using CMR was determined by analysing the receiver operating characteristic curves. The validation cohort enrolled 2,663 patients with STEMI who underwent PPCI within 12 h of symptom onset from January 2012 to April 2022 across 5 medical centres. All patients were followed up for at least 1 year. The primary endpoint was the occurrence of major adverse cardiovascular events (MACE), including cardiac death, hospitalisation for heart failure, repeat myocardial infarction, and target lesion revascularisation.

Results: The derivation cohort identified an AMR cutoff >26.6 mmHg*s/dm for predicting CMD post-PPCI (area under the curve 0.721, 95% confidence interval [CI]: 0.677-0.763). Multivariable logistic regression analysis indicated that AMR >26.6 mmHg*s/dm was a CMD risk factor (odds ratio 4.10, 95% CI: 2.56-6.56; p<0.001). The MACE incidence was significantly higher among patients in the validation cohort with AMR >26.6 mmHg*s/dm than among those with AMR ≤26.6 mmHg*s/dm (30.9% vs 21.5%, adjusted hazard ratio [HR] 1.47, 95% CI: 1.20-1.80; p<0.001). MACE incidence increased with AMR, with an adjusted HR of 1.30 (95% CI: 1.17-1.46; p<0.001) per 10 mmHg*s/dm increase. The Bland-Altman and Kappa analyses showed good intra- and interobserver agreement for AMR (intraobserver: bias=-0.104, k=0.914; interobserver: bias=-0.032, k=0.958).

Conclusions: AMR >26.6 mmHg*s/dm predicts CMD during PPCI and increased MACE incidence in patients with STEMI. This convenient tool helps in risk stratification and treatment guidance for STEMI prognosis.