"Atrial fibrillation is believed to double the risk of death and quadruple the risk of strokes," coauthor Concepcion Moro, M.D., says. "In addition, atrial fibrillation may accompany many cardiac conditions such as valvular heart disease, cardiomyopathies, and ischemic heart disease. It can also appear along with high blood pressure and other systemic diseases such as hyperthyroidism, although in many patients the cause is unknown."

According to Moro, the dysrhythmia is typically treated with antiarrhythmic drugs such as amiodarone, anticoagulants, and electrical cardioversion. However, new therapeutic options are needed because the dysrhythmia frequently recurs despite treatments.

"The clue for this work was evidence that patients treated with angiotensin II antagonists for other conditions developed fewer atrial arrhythmias than expected," she explains.

In the study, 154 patients who had continuous atrial fibrillation for more than seven days were randomized to one of two treatments: amiodarone or amiodarone plus irbesartan. All of the patients were scheduled to have electrical cardioversion three weeks after initiation of therapy.

At the three-week point, 62 patients had stable heart rhythms on medication alone and 92 received electrical cardioversion, which was successful in 83 patients. During the next two months, 26 patients had a recurrence of atrial fibrillation. An analysis found that the two-month probability of maintaining a normal rhythm was nearly 85 percent for subjects who received irbesartan compared with 63 percent for those who received only amiodarone.

"Our analysis revealed that using the angiotensin II receptor antagonist was the only significant variable related to maintaining heart rhythm after cardioversion," the researchers write.

One of the most important factors to predict recurrence was duration of dysrhythmia before randomization.

"There were a very low number of adverse events, well within the expected limits, and the incidence rate was similar in both groups," Moro notes. One 51-year-old man in the group receiving both drugs had sudden cardiac death three weeks after successful cardioversion, but researchers believe the death was unrelated to the procedure because of the time lag. In addition, three patients in the group receiving amiodarone and two in the group receiving both drugs had adverse events requiring discontinuance of therapy.