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

Abstract

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.

Figure 1: Selection of studies for meta-analysis.

Figure 2: Meta-analysis of implantable cardioverter defibrillator discharge in studies of fish-oil supplementation. Significant heterogeneity was detected between trials (p = 0.04). Note: CI = confidence interval.

Figure 3: Sensitivity analysis of the trials by (A) Leaf et al and Brouwer et al; (B) Raitt et al and Brouwer et al; and (C) Raitt et al and Leaf et al. Significant heterogeneity was detected between the trials by Raitt et al and Leaf et al (p = 0.01). Note: CI = confidence interval. *Number of participants who experienced an implantable cardioverter defibrillator discharge.

Figure 4: Meta-analysis of all-cause mortality in studies of fish-oil supplementation among patients with implantable cardioverter defibrillators. No significant heterogeneity was detected (p = 0.29). Note: CI = confidence interval.