Coronary collateral circulation and mortality in ST-elevation myocardial infarction undergoing primary PCI: an updated systematic review and meta-analysis of 18,443 patients

Abstract Background Coronary collateral circulation may limit myocardial injury during ST-elevation myocardial infarction (STEMI), but the magnitude of this association with mortality in contemporary practice remains unclear. We conducted an updated meta-analysis to reassess the relationship between collateral status and mortality in STEMI patients undergoing primary percutaneous coronary intervention (PCI). Methods We searched PubMed, Embase, and Scopus (March 2020–January 2026) to update the meta-analysis by Allahwala et al. Studies comparing mortality between robust versus poor collaterals were included. Random-effects meta-analysis was performed. Results Twenty-six studies comprising 18,443 patients were included (19 studies from the original meta-analysis plus 7 new studies). In the primary analysis of 17 studies using standard Rentrop definitions (15,493 patients), robust collaterals were associated with significantly lower mortality (OR 0.52; 95% CI 0.39–0.71; p < 0.0001; I²=38%). This corresponded to an absolute risk reduction of 2.7%. Importantly, the 3 new studies showed attenuated effects (OR 0.88; 95% CI 0.49–1.58) compared to the 14 original studies (OR 0.47; p = 0.06 for subgroup difference). Meta-regression identified higher baseline mortality as a predictor of larger effect sizes (p = 0.038). The certainty of evidence was LOW (GRADE). Conclusions Robust coronary collaterals are associated with lower mortality in STEMI patients undergoing primary PCI. However, the apparent attenuated association in contemporary studies likely reflects statistical dilution due to lower baseline mortality rather than diminished biological relevance of collaterals. Given the LOW certainty of evidence from observational data, collateral assessment should be considered prognostic rather than a basis for interventions. Review registration (PROSPERO Registration ID: CRD420261278634) Clinical trial number Not Applicable (As this is a Systematic Review and Meta-Analysis and not a clinical trial). Graphical Abstract Central Illustration