Collateral Blood Supply May Cut Death Risk in CAD
By Todd Neale, Senior Staff Writer,
October 02, 2011
Action Points
Explain that patients who have coronary artery disease (CAD) and strong coronary collateral circulation appear to have improved survival.
Point out that the risk reduction was more pronounced in studies in which most patients underwent percutaneous coronary intervention, and those in which the collateral circulation was assessed using intracoronary pressure measurements versus visual inspection.
Review
Patients who have coronary artery disease (CAD) and strong coronary collateral circulation appear to have improved survival, a meta-analysis showed.
For patients with stable or acute CAD, a high degree of collateralization was associated with a 36% reduction in the risk of dying during follow up for as long as 10 years (RR 0.64, 95% CI 0.45 to 0.91), according to Christian Seiler, MD, of the University Hospital Bern in Switzerland, and colleagues.
The risk reduction was more pronounced in two types of studies: those in which most patients underwent percutaneous coronary intervention (PCI) versus those with no PCI (RR 0.42 versus 0.70), and those in which the collateral circulation was assessed using intracoronary pressure measurements versus visual inspection (RR 0.38 versus 0.71), the researchers reported online in the European Heart Journal.
Coronary collateral circulation is found in individuals with and without coronary artery disease. If one of the epicardial arteries becomes blocked, the collateral arteries can enlarge to provide an alternative source of blood to the heart.
"The coronary collaterals may represent a useful prognostic marker," they wrote. "Patients with a low collateralization have an increased mortality risk and may be monitored more closely."
They added that diagnostic angiography remains important to define the coronary anatomy and the degree of collateralization, which is best accomplished by measuring the intracoronary pressure; an alternative is to use an intracoronary ECG.
The researchers stated that for patients with an MI, increased collateralization has been associated with the following:
Smaller infarct size
Preserved cardiac function after an acute infarction
Reduced post-infarct ventricular dilatation
Reduced post-infarct aneurysm formation
But the relationship between increased collateralization and mortality is less clear.
Seiler and colleagues performed a meta-analysis of 12 studies that included 6,529 patients with stable or acute CAD and reported the degree of coronary collateralization and mortality statistics.
The lower mortality risk with a high degree of collateralization was consistent in patients with stable disease (RR 0.59, 95% CI 0.39 to 0.89), those with subacute MI (RR 0.53, 95% CI 0.15 to 1.92), and those with acute MI (RR 0.63, 95% CI 0.29 to 1.39). The differences among the relative risks were not statistically significant (P=0.149).
The researchers noted that the lack of statistical significance for the relationship in the MI groups was mostly due to limited power from a small sample size.
Although a causal relationship between better collateralization and mortality could not be established, the authors speculated on some possible underlying mechanisms.
Collateral circulation has been shown to reduce QT interval prolongation resulting from acute myocardial ischemia, which puts patients at risk for fatal arrhythmias, they wrote.
In addition, they noted that reductions in infarct size and post-infarct ventricular dilatation and preservation of cardiac function likely have mortality benefits.
"The results of this study highlight the importance of finding means to induce collateral growth," Seiler and colleagues wrote, adding that experimental studies have shown that promoting growth is feasible.
"We further need larger-scale interventional studies which test whether the therapeutic promotion of collaterals translates into improved clinical outcomes," they wrote.
They acknowledged that the analysis was limited in that all of the included studies were observational and most were small and retrospective.
The study was supported by the Swiss National Science Foundation.
The authors reported that they had no conflicts of interest.
Primary source: European Heart Journal
Source reference:
Meier P, et al "The impact of the coronary collateral circulation on mortality: A meta-analysis" Eur Heart J 2011.
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