INTRODUCTION: The coronary collateral circulation (CCC) is an alternative source of blood supply in coronary artery disease (CAD). The prognostic value of the presence of CCC at the time of acute coronary syndrome (ACS) is undefined with regards to hard outcomes, particularly reduction in mortality. The study's aim is to determine if the presence of CCC demonstrated by coronary angiography during an ACS is associated with a reduction in mortality. 

METHODS: We conducted a systematic search of studies using MEDLINE, EMBASE, ScienceDirect, Scopus, and Cochrane Central Register of Controlled Trials databases in all languages and examined reference lists of studies. The inclusion criteria were 1) observational; 2) population included adults >19 years old with an acute coronary syndrome; 3) reported data on mortality in association with the presence or absence of CCC on angiography; and 4) should have controlled for confounders by using logistic regression analysis. Study quality was assessed using the Newcastle-Ottawa Quality Assessment Scale for observational studies. The outcome of interest was reduction in all-cause mortality, assessed using Mantel-Haenzel analysis of random effects to compute for risk ratios.

RESULTS: Pooled analysis from 11 identified trials with 8,370 subjects showed that among patients with ACS who underwent coronary angiography, the presence of CCC showed a trend towards benefit in terms of mortality, but was not statistically different from those without CCC [RR 0.65, (95% CI 0.38 to 1.12), p<0.0001, I2=74%]. In those ACS patients with CCC treated with PCI, a significant reduction in mortality was found [RR 0.43, (95% CI 0.29 to 0.64), p< 0.0001, I2=0%].

CONCLUSION: The presence of CCC during ACS showed a trend towards mortality reduction. Further, among patients treated with PCI, those with CCC had an incrementally significant reduction in mortality compared to those without CCC.