Microvascular function, plaque characteristics and prognostic effect in STEMI with early spontaneous reperfusion: Insights from intravascular ultrasound and coronary physiology
Authors: Li Xida , Sun Shuo , Wu Lanfang , Luo Demou , Ye Jingguang , Guo Xiaosheng , Xu Shenghui , Sun Boyu , Zhang Youting , Yang Xing , Zhou Yingling , Xi Pu Bu Zha , Dong Haojian , Luo Jianfang 
Published: September 2023

Purpose
Early spontaneous reperfusion (ESR) in ST-elevation myocardial infarction (STEMI) usually indicates better vascular circumstance and less ischemic injury. The relationship between microvascular function, plaque characteristics and prognostic results of ESR during primary percutaneous coronary intervention (pPCI) is unclear. We sought to explore microvascular function and intravascular characteristics in STEMI patients with different states of reperfusion using intravascular ultrasound (IVUS) and angiography-derived quantitative flow ratio (QFR)/microcirculatory resistance (AMR).
Methods
Post-hoc analysis was performed in patients with acute STEMI and high thrombus burden from our prior multi-center, prospective cohort study (ChiCTR1800019923).STEMI patients who underwent pPCI and IVUS imaging were analyzed. The ESR phenomenon was defined as any blood flow of thrombolysis in myocardial infarction (TIMI) 2 or 3 recorded by Quantitative Coronary Angiography (QCA) before intervention. QFR and AMR were performed on angiographic images acquired before and after pPCI. They were divided into ESR group and occlusion group (blood flow of TIMI 0 or 1 before intervention). The patients were followed-up for 24 months after PCI. Major cardiac adverse events (MACEs) included cardiac death, stroke, myocardial infarction, heart failure and all-cause death.
Results
A total of 112 patients were enrolled with ESR group (27, 24.1%) and occlusion group (85, 75.9%). IVUS showed plaque rupture (ESR 18, 66% vs. occlusion 63, 74% p = 0.01), ratio of lipid pool (ESR 14, 51.8% vs. occlusion 49, 57.6%, p = 0.01), lipid plaque (ESR 10.1% vs. occlusion 11.6%, p = 0.03) and necrotic plaque ratio (ESR 27.3% vs. occlusion 28.7%, p = 0.02) were less common in the ESR group. Microvascular functional analysis showed ESR group had lower MR (ESR 167.8 original, 177.5 final vs. occlusion group 206.6 original, 269.4 final, p = 0.01, between groups) and higher flow speed (ESR 17.9 original, 19.0 final vs. occlusion group 13.5 original, 15.0 final, p = 0.02, between groups). Multivariable regression showed ESR predicts better mircrovascular function with lower final MR (HR= -13.7, p = 0.04, 95% CI: -35.7 ~ -8.3) and faster final flow speed (HR = 3.77, p = 0.01, 95% CI: 2.13 ~ 5.41) compared to occlusion group with higher final MR (HR = 36.4, p = 0.01, 95% CI: 1.56 ~ 65.3) and slower final flow speed (HR=-7.3, p = 0.001, 95% CI: -11.4~-3.1). Meanwhile ESR was a protective factor of no-reflow (HR = 0.75, p = 0.03) and MACE (OR = 0.91, p = 0.02). Occlusion group was a risk factor of MACE (HR = 1.94, p = 0.04) and no-reflow (HR = 1.72, p = 0.01).
Conclusion
The states of reperfusion are related with microvascular resistance. ESR phenomenon is associated with lower final microvascular resistance and faster final flow speed compared to occlusion group. More stable and non-ruptured plaques with less lipid cores, less necrotic cores which may be the mechanism of ESR in STEMI patients.