Association of endothelial glycocalyx degradation with post-PCI slow flow phenomenon in STEMI patients: a prospective observational study.

Background: The coronary slow flow (CSF) phenomenon following primary percutaneous coronary intervention (PPCI) for acute ST-segment elevation myocardial infarction (STEMI) represents a severe complication associated with adverse clinical outcomes. The endothelial glycocalyx (EG) serves as a pivotal barrier maintaining microvascular integrity; however, the kinetics of its degradation and its specific association with CSF remain incompletely understood. Therefore, this study aims to investigate the correlation between serum markers of EG shedding and the incidence of CSF in patients with STEMI. Methods: In this prospective observational study, we consecutively enrolled 82 patients with STEMI who underwent emergent percutaneous coronary intervention (PCI) between August and November 2025. CSF was defined as a post-procedural corrected thrombolysis in myocardial infarction (TIMI) frame count (CTFC) >27 frames. Post-procedural TIMI flow grade was recorded concurrently, and no-reflow was defined as TIMI flow grade <3. Serum syndecan-1 (SDC-1) and hyaluronic acid (HA) were measured pre-procedure, immediately after PCI, and 24 hours after PCI. Multivariable logistic regression was used to evaluate the association between pre-procedural biomarkers and CSF, with continuous variables standardized as z-scores. As sensitivity analyses, we performed linear regression using CTFC as a continuous outcome and Firth's penalized logistic regression for no-reflow. Discriminative performance was assessed using receiver operating characteristic (ROC) curves. Results: Compared with the normal flow group, the CSF group had higher pre-procedural levels of SDC-1 and HA. Longitudinal analyses showed a more pronounced immediate post-PCI increase in HA in the CSF group, which remained elevated at 24 hours. Both SDC-1 and HA also remained higher at 24 hours in the CSF group. After adjustment for age, symptom-to-treatment time, total stent length, and admission diastolic blood pressure, higher pre-procedural SDC-1 [odds ratio (OR) =5.03; 95% confidence interval (CI): 2.39-10.60; P<0.001] and HA (OR =3.56; 95% CI: 1.92-6.60; P<0.001) were independently associated with CSF. These associations were directionally consistent in sensitivity analyses using CTFC as a continuous outcome and no-reflow as an endpoint. ROC analysis showed that pre-procedural SDC-1 had higher discriminative ability [area under the curve (AUC) =0.88] than HA (AUC =0.84). Conclusions: Severe degradation of the EG, characterized by elevated serum levels of SDC-1 and HA, is independently associated with the post-procedural CSF phenomenon in patients with STEMI. Pre-procedural SDC-1 appeared to have a stronger association with CSF and numerically higher discriminative performance than HA. These findings suggest that therapeutic strategies aimed at preserving the glycocalyx may offer novel avenues for ameliorating coronary microvascular dysfunction. The study was registered in the Chinese Clinical Trial Registry (Identifier: ChiCTR2500107421).