Shannon Best, McHenry Mauger, Addison Nguyen, Mohammadali M Shoja, Stephen Ely
Many factors influence outcomes in patients with coronary artery disease (CAD) and acute myocardial infarction (AMI), including patient demographics, comorbidities, cardiac function, clinical presentation, and revascularization therapies. Percutaneous coronary intervention (PCI) is associated with reduced infarct size (IS) and improved left ventricular ejection fraction (LVEF), which have both been shown to reduce all-cause mortality and hospitalization for heart failure following AMI. Coronary collateral circulation may also have a protective effect in CAD and, like PCI, may play a role in limiting IS and improving LVEF after AMI. In this systematic review and meta-analysis, our objective was to investigate the impact of coronary collaterals on IS and LVEF after AMI. A search of Embase, Web of Science, and PubMed from 1980 onwards was conducted in July 2025 using the keywords "coronary collaterals", "myocardial infarction", and "infarct size." A total of six studies (n=820) were included for review, which compared IS and LVEF measured by cardiac magnetic resonance imaging (CMR) between patients with poor and good collaterals after undergoing PCI for AMI. Mean difference (MD) was calculated, and both the common effect and random effects models were conducted to pool effect sizes. IS was consistently larger in patients with poor collaterals. The random effects model gave a statistically significant pooled mean difference (MD) of 5.19 (95% CI = 0.99, 9.40, Z = 3.18, p = 0.024). Studies reported mixed results regarding LVEF, and the random effects model gave us a pooled MD -2.62 (95% CI = -5.36, 0.11, Z = -2.03, p = 0.056), which was not statistically significant. In conclusion, we found that in patients presenting with AMI, greater development of coronary collaterals is associated with a significant reduction in IS. Clinically, this finding is important as a smaller IS is associated with a reduction in long-term mortality and hospitalization for heart failure after AMI treated with primary PCI. We also found a trend toward improved LVEF in patients who experienced AMI with more extensive collaterals, although these results were not significant. Based on these results, the impact of coronary collaterals on IS rather than LVEF may be a more promising area of research for improving patient survival after AMI.