BROOKLYN, NEW YORK. Fish oils and its main components eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have electrophysiological and anti-inflammatory effects which would be expected to be beneficial in the primary (initial episode) and secondary (recurrence) prevention of atrial fibrillation (AF). For example, fish oils inhibit the sodium and calcium currents in myocytes (heart cells) and enhance potassium currents. They also increase membrane fluidity, decrease inflammation and oxidative stress, and increase effective refractory periods (ERPs), thus decreasing the time interval during which the heart is vulnerable to initiation of an AF episode. Furthermore, fish oil increases vagal activity and improves the function (emptying velocity and fraction) of the left atrial appendage. There is also substantial evidence that fish oil reduces the incidence of fatal coronary heart disease and sudden cardiac death.

With all these benefits, one would expect fish oils to be effective in preventing both the initiation and recurrence of AF. Unfortunately, there is no consensus that this is universally the case. Electrophysiologists associated with the SUNY Downstate Medical Center have just published a review detailing what is known about the efficacy of fish oils in the primary and secondary prevention of AF. Highlights of their findings follow.

• Continuous fish oil supplementation decreases the risk of developing new-onset AF in patients without structural heart disease.

• Supplementation with high-dose (more than 6 grams/day) fish oil for more than a month reduces the risk of AF episodes originating in the pulmonary veins and reduces heart rate during episodes of paroxysmal AF.

• Fish oil supplementation is beneficial in the primary prevention of AF in the elderly with structural heart disease, but may be detrimental in younger patients with vagal AF. NOTE: Fish oil increases vagal tone.

• There is some evidence from animal studies that fish oil, especially EPA, decreases fibrosis resulting from inflammation.

• No clear evidence exists that fish oil supplementation decreases the risk of recurrence in paroxysmal AF. However, there is evidence that supplementation decreases the risk of early recurrence in patients having undergone a pulmonary vein isolation procedure. This is no doubt related to the anti-inflammatory properties of fish oils. Several clinical trials are underway to finally settle the question � Is fish oil useful in preventing AF recurrence in paroxysmal and persistent AF?

• Several clinical trials have been carried out to determine if fish oil supplementation prior to and following coronary artery bypass surgery prevents post-operative AF. Some trials show a benefit, while others do not; however, it is clear that supplementation is associated with a shorter hospital stay, shorter stay in the intensive care unit, and a reduction of post-operative complications.