Since the original observations that Greenland Eskimos eating a diet high in omega-3 polyunsaturated fats (PUFAs) from sea mammals and fish had an unexpectedly low risk of cardiac death, multiple lines of evidence have suggested that omega-3 PUFAs have antiarrhythmic properties, according to background information in the article. Several clinical trials have shown that dietary changes or supplements to increase omega-3 PUFA intake result in a reduced risk of sudden death without a consistent change in risk of heart attack.

Merritt H. Raitt, M.D., of Oregon Health and Science University and the Portland VA Medical Center, Portland, Ore., and colleagues conducted a study to determine if fish oil supplements would have antiarrhythmic properties in patients with a recent episode of sustained ventricular arrhythmia. The double-blind, placebo-controlled trial was performed at 6 U.S. medical centers with enrollment from February 1999 until January 2003. The study included 200 patients with an implantable cardioverter defibrillator (ICD) and a recent episode of sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). Patients were randomly assigned to receive fish oil, 1.8 g/d, 72 percent omega-3 PUFAs, or placebo and were followed up for a median of 718 days.

The researchers found that at 6, 12, and 24 months, 46 percent, 51 percent, and 65 percent of patients randomized to receive fish oil had ICD therapy for VT/VF compared with 36 percent, 41 percent, and 59 percent for patients randomized to receive placebo. In the subset of 133 patients whose qualifying arrhythmia was VT, 61 percent, 66 percent, and 79 percent of patients in the fish oil group had VT/VF at 6, 12, and 24 months compared with 37 percent, 43 percent, and 65 percent of patients in the control group. Recurrent VT/VF events were more common in patients randomized to receive fish oil.

"This study was undertaken to better understand the previously observed reduction in sudden death mortality after myocardial infarction associated with fish oil supplementation. The fact that we were not able to demonstrate an antiarrhythmic effect of fish oil does not call into question the potential benefits of fish oil or dietary fish intake in patients who have had a myocardial infarction. Instead, our results suggest that the mechanism of benefit, if due to antiarrhythmic properties, may not be due to the suppression of reentrant VT or VF. The lack of benefit and the suggestion that fish oil supplementation may increase the risk of VT or VF in some patients with ICDs can reasonably be interpreted as evidence that the routine use of fish oil supplementation in patients with ICDs and recurrent ventricular arrhythmias should be avoided," the authors conclude.

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