* Patients used a high-dose prescription form of fish oil
* No benefit seen after six months (Adds company, researcher comments throughout)
By Julie Steenhuysen
CHICAGO, Nov 15 (Reuters) - Taking a high dose of fish oil does not prevent symptoms of atrial fibrillation, a common heart rhythm problem that can cause strokes, U.S. researchers said on Monday.
Several small trials have hinted that omega-3 fatty acids from fish oil might improve treatment of atrial fibrillation, which affects an estimated 2.2 million Americans.
But a study of more than 600 patients who took GlaxoSmithKline's (GSK.L) prescription-strength fish oil drug, known as Lovaza, for six months showed it did not keep the heart rhythm problem from coming back, researchers told the American Heart Association meeting in Chicago.
"This was a study that showed no benefit," said Dr. Robert Eckel, professor of medicine at the University of Colorado and a past president of the American Heart Association.
"There has been some evidence that fish oil supplements may be beneficial because of their effect on abnormal cardiac rhythms. This study really challenges that view," Eckel, who was not involved in the study, said in a telephone interview.
In people with atrial fibrillation, the heart's two small upper chambers, the atria, quiver instead of beating efficiently, allowing blood to pool. This can form clots that travel to the brain and cause strokes.
Atrial fibrillation is treated with a battery of therapies. Anti-arrhythmic drugs can help restore a normal rhythm; beta blockers, digitalis, calcium channel blockers or amiodarone can help slow the heart rate.
People often take the blood thinner warfarin to prevent strokes, and radiofrequency energy is sometimes used to destroy tissues that cause the irregular heartbeat.
Dr. Peter Kowey of the Lankenau Institute for Medical Research in Wynnewood, Pennsylvania, and colleagues studied a high-dose, purified formula of omega-3 from fish oil for preventing recurrent atrial fibrillation.
The study, which was also released online in the Journal of the American Medical Association, included 663 U.S. patients who were prone to sudden attacks of atrial fibrillation, and a small group who had persistent symptoms.
People in the study got either prescription fish oil or a placebo. They also took beta blockers and ACE inhibitors or angiotensin receptor blockers, but no anti-arrhythmic drugs. After 6 months of follow-up, the researchers found fish oil offered no benefit in this group of patients.
Dr. Christine Albert of Brigham and Women's Hospital in Boston said other studies are being done to see if the drug might prevent people from developing atrial fibrillation, but Kowey said he thought it was unlikely.
"The fact that this drug failed in this population makes it highly unlikely that you would be able to prove efficacy in other groups," Kowey told a news briefing.
In a statement, Glaxo said it will continue to review data from the study in the context of other studies with Lovaza and other fish oil treatments, but, "in this patient population, there was clearly no benefit from Lovaza."