Atrial fibrillation (AF) is a heart rhythm disorder that usually involves a rapid heart rate. People who take fish oil supplements may reduce the risk of a recurrence of AF. This study will evaluate the effectiveness of fish oil at decreasing the recurrence of AF and will examine the reasons why fish oil may reduce this risk.

AF is the most common type of serious heart arrhythmia. It affects approximately 2% of the population and is becoming more common. In AF, the heart's atria, or upper chambers, contract in a very disorganized and abnormal manner and are unable to correctly pump blood into the heart's ventricles, or lower chambers. Symptoms may include a rapid or irregular pulse, dizziness, fainting, or breathing difficulty. Recent studies suggest that inflammation plays a fundamental role in the development of AF. Inflammation, and the resulting oxidative stress, can cause cellular and tissue damage. In turn, this may alter heart function, potentially leading to both the onset and recurrence of AF. Markers of inflammation, such as C-reactive protein (CRP) and interleukin-6 (IL-6), are often elevated in patients with AF, providing further evidence of inflammation's role. While there are several treatment options for AF, they are usually only moderately effective. Previous research has shown that fish oil supplements have anti-inflammatory, antifibrotic, and antioxidant effects and can reduce the risk of AF following surgery. However, it is not known exactly how fish oil reduces this risk and whether the same positive effect will carry over in people who experience the more common type of AF that is unrelated to surgery. The purpose of this study is to evaluate the effectiveness of fish oil supplementation at decreasing the recurrence of AF in adults who have not undergone recent surgery. Researchers will also examine the ways in which fish oil reduces AF recurrence.

This study will enroll people who have had at least two occurrences of AF. Participants will be randomly assigned to receive either fish oil supplements or placebo for 24 weeks. At study visits at baseline and Weeks 2, 4, 8, 12, 18, and 24, participants will undergo a medical and social history review, a physical exam, and blood and urine collection. At the baseline study visit, an electrocardiogram will also occur.

Inclusion Criteria:

• >=21 years of age
• a history of atrial fibrillation
• a history of at least two occurrences of atrial fibrillation or atrial flutter, at least one of which is atrial fibrillation
• an electrocardiogram that was recorded within 12 months of randomization showing atrial fibrillation or atrial flutter
• sinus rhythm at the time the first dose of randomized medication is taken
• stable antiarrhythmic medications
• if the patient has had an ablation for atrial fibrillation or flutter or a MAZE procedure, the qualifying episode of atrial fibrillation must have occurred at least 3 months post-procedure
• normal serum potassium level within the last 28 days
• provided informed consent

Exclusion Criteria:

• permanent atrial fibrillation or flutter
• New York Heart Association class III or IV heart failure or Canadian Cardiovascular Society class III or IV angina pectoris
• cardiac or thoracic surgery within the previous 3 months
• acute pericarditis within the previous 3 months
• other reversible causes of atrial fibrillation such as thyrotoxicosis
• acute myocardial infarction or unstable angina within the previous 3 months
• history of neurologic event (TIA or stroke)within the past 3 months
• history of acute congestive heart failure precipitated by atrial fibrillation, and the patient is not receiving rate-control therapy
• Wolff-Parkinson-White syndrome
• a medical condition that is likely to be fatal in less than one year
• active, uncontrolled co-morbid inflammatory condition (e.g., rheumatoid arthritis, inflammatory bowel disease, SLE)
• receiving cytotoxic chemotherapy or radiotherapy for cancer
• taking a fish oil supplement
• allergic to fish
• bleeding event not related to trauma or surgery requiring hospitalization or transfusion in previous year
• systolic blood pressure < 90 mm Hg or heart rate <50 beats/minute
• history of ventricular fibrillation or sustained ventricular tachycardia, or presence of an implanted defibrillator placed for the occurrence of such an event or the presence of an Implantable Cardioverter-Defibrillator (ICD) that has discharged appropriately for a ventricular arrhythmia
• pregnant or breast feeding
• enrollment in another research study involving an intervention
• on dialysis or recipient of a renal transplant
• use of potentially cardiotoxic illegal drugs (cocaine, methamphetamine, opioids) in the last 12 months
• Treated for alcoholism and currently drinking alcohol to excess or alcoholic cardiomyopathy as the primary clinical diagnosis and currently drinking alcohol to excess
• presence of an iron-storage disease, such as hemochromatosis, transfusional hemosiderosis, or those subjects in whom a daily dose of up to 20 mg elemental iron (in and of itself or in addition of current iron supplementation) would post a risk for toxicity from iron overload
• subjects receiving or anticipated to receive intravenous iron therapy

Adverse event data were collected during the 24 week study, after participants took first dose of study medication or placebo.

We determined recurrence of Atrial Fibrillation(AF) by both routine and symptomatic TTM transmissions. We did not examine the effect of therapy on total AF burden. Sample size was relatively small, and included a heterogeneous patient population.