Toronto, ON - A small meta-analysis published last week, which attempted to address the inconsistencies in the data on fish-oil supplementation in patients with implantable cardioverter defibrillators (ICDs), suggests that there is significant heterogeneity in cardiac patients' responses to the long-chain fatty acids [1].

Published in the January 15, 2008 issue of the Canadian Medical Association Journal, the researchers, led by Dr David Jenkins (University of Toronto, ON), say the reasons for observed differences in response are not clear but conclude that "caution should be used when prescribing fish-oil supplementation for patients with ventricular tachycardia."

The meta-analysis included three trials presented and published in the past few years, all reported by heartwire: the Study on Omega-3 Fatty Acids and Ventricular Arrhythmia (SOFA) [2], a trial showing that supplementation with fish-oil capsules over one year did not reduce the risk of ventricular tachycardia/ventricular fibrillation (VT/VF) or death in patients with secondary-prevention ICDs; a study by Dr Merritt Raitt (Oregon Health and Science University, Portland) et al showing that the use of fish-oil supplements over two years failed to protect against VT/VF in patients who had received an ICD because of recent sustained ventricular arrhythmia [3]; and a study by Dr Alexander Leaf (Harvard Medical School, Boston, MA) and colleagues showing that regular ingestion of fish-oil fatty acids for 12 months failed to reduce the risk of potentially fatal ventricular arrhythmias in patients with secondary-prevention ICDs [4].

In the study by Leaf and colleagues, however, an "on-treatment" analysis hinted that there was a longer time to first ICD event for VT/VF or death from any cause among patients randomized to fish oil than among those randomized to olive-oil placebo.

The meta-analysis of ICD discharge in the three studies of fish-oil supplementation showed that the prescription of fish oil to these patients failed to reduce arrhythmia. In a meta-analysis of all-cause mortality, an outcome common to all three studies, the overall relative risk was nonsignificant.

Jenkins and colleagues point out that two other meta-analyses failed to "show a clear advantage of increased fish-oil consumption, either for secondary prevention of coronary heart disease or restenosis after angioplasty." They note, however, that fish oils have complex and pleiotropic effects on the heart," including blocking cardiac ion channels, reducing fibrosis in response to mechanical stress, decreasing blood coagulation, reducing serum triglycerides, and possibly altering immune function." Moreover, drug-nutrient interactions, such as fish oil with antiarrhythmic medications, might be partly responsible for the observed differences between studies.

They conclude by stating that further research is needed, but, "at present, the use of fish oils in patients with implantable cardioverter defibrillators appears to warrant caution."