Fish-oil supplementation in patients with implantable cardioverter defibrillators: a meta-analysis

Background

A recent Cochrane meta-analysis did not confirm the benefits of fish and fish oil in the secondary prevention of cardiac death and myocardial infarction. We performed a meta-analysis of randomized controlled trials that examined the effect of fish-oil supplementation on ventricular fibrillation and ventricular tachycardia to determine the overall effect and to assess whether heterogeneity exists between trials.

Methods

We searched electronic databases (MEDLINE, EMBASE, The Cochrane Central Register of Controlled Trials, CINAHL) from inception to May 2007. We included randomized controlled trials of fish-oil supplementation on ventricular fibrillation or ventricular tachycardia in patients with implantable cardioverter defibrillators. The primary outcome was implantable cardioverter defibrillator discharge. We calculated relative risk [RR] for outcomes at 1-year follow-up for each study. We used the DerSimonian and Laird random-effects methods when there was significant heterogeneity between trials and the Mantel-Hanzel fixed-effects method when heterogeneity was negligible.

Results

We identified 3 trials of 1–2 years'' duration. These trials included a total of 573 patients who received fish oil and 575 patients who received a control. Meta-analysis of data collected at 1 year showed no overall effect of fish oil on the relative risk of implantable cardioverter defibrillator discharge. There was significant heterogeneity between trials. The second largest study showed a significant benefit of fish oil (relative risk [RR] 0.74, 95% confidence interval [CI] 0.56–0.98). The smallest showed an adverse tendency at 1 year (RR 1.23, 95% CI 0.92–1.65) and significantly worse outcome at 2 years among patients with ventricular tachycardia at study entry (log rank p = 0.007).

Conclusion

These data indicate that there is heterogeneity in the response of patients to fish-oil supplementation. Caution should be used when prescribing fish-oil supplementation for patients with ventricular tachycardia.There is a public perception that fish and fish oil can be recommended uniformly for the prevention of coronary artery disease.^1–3 However, the scientific evidence is divided^4,5 and official agencies have called for more research.⁶It is estimated that 0.5% of patients with coronary heart disease, 1% of patients with diabetes or hypertension and 2% of the general population at low risk of coronary heart disease take fish-oil supplements.⁷ In 2004, the price of fish oils overtook that of vegetable oils, and in 2006, the price rose to US$750 per ton.⁸ The value of fish oil as a nutraceutical in the European market was US$194 million in 2004, and it is anticipated that the price will continue to rise as availability declines.⁸ Canada is both a consumer and an exporter of fish oil, and it exported 15 000 tons in 2006.⁹The scientific debate over the clinical value of fish oil is highlighted by a recent Cochrane review, which concluded that long-chain omega-3 fatty acids (eicosapentaenoic acid and docosahexaenoic acid) had no clear effect on total mortality, combined cardiovascular events or cancer.⁴ Furthermore, another recent meta-analysis¹⁰ only showed a significant positive association between fish-oil consumption and prevention of restenosis after coronary angioplasty in a select subgroup after excluding key negative papers.¹¹ Finally, the antiarrhythmic effect, which is proposed to be the principal mechanism of their benefit in cardiovascular disease, has not been demonstrated clearly in clinical trials.^12–14We therefore performed a meta-analysis of randomized controlled trials that examined the effect of fish-oil supplementation in patients with implantable cardioverter defibrillators who are at risk of ventricular arrhythmia to determine the overall effect of fish oils. We also sought to investigate whether there was significant heterogeneity between trials.