Patients with stable coronary artery disease (CAD) who had high coronary collateral circulation (CCC) showed a significantly reduced mortality risk compared with patients with low collateralization, according to the results of a meta-analysis published online Oct. 3 in the European Heart Journal.
CCC, which is present in patients with and without CAD, has shown benefits in cases of MI but its general impact on mortality in CAD patients is not clear, Pascal Meier, MD, of the Heart Hospital at University College London Hospitals in London, and colleagues noted. To assess survival, they conducted a meta-analysis based on 12 studies that looked at the association of mortality and the degree of coronary collateralization.
They searched EMBASE, PubMed, BIOS and ISI Web of Science between 1980 and April 2011 and scoured abstracts and conference listings to identify prospective studies that reported on mortality and CCC. Retrospective case-control studies were not included. Two investigators reviewed a total of 123 articles. The two investigators needed to agree the study addressed the association of mortality and the degree of coronary collateralization to be included in the meta-analysis.
Data from 12 studies and 6,529 participants then were combined to estimate the pooled impact of high versus low collateralization. The meta-analysis primary endpoint was all-cause mortality, with the exception of one study that provided results only on cardiovascular mortality.
The meta-analysis found that CAD patients with high collateralization had a 36 percent reduced mortality risk compared with patients with low collateralization. The risk ratio was 0.59 for patients with stable CAD and high collateralization and 0.63 for patients with acute MI and high collateralization.
“The meta-analysis of 12 studies and 6,529 patients shows that the CCC is associated with relevantly improved survival,” Meier and colleagues wrote. “The result was consistent whether patients underwent PCI or a diagnostic angiogram only, and whether collaterals were assessed visually or with CFI [collateral flow index].”
The authors suggested that coronary collaterals could serve as a prognostic marker using methods such as diagnostic angiography and intracoronary electrocardiograms to identify patients with low collateralization. They argued that their results also supported the need for clinical evaluations of therapies that promote collateral growth to determine whether the therapies improve survival.
The meta-analysis had several limitations linked to the 12 studies, they noted. The studies were small, observational, had no standardized definition of some terms, had different primary objectives and their data did not capture the dynamics of coronary collateral functions. They added that future prospective studies can avoid these shortcomings if they are large, protocol-driven, include well-defined endpoints, use quantitative measurements and control for confounders.