STOCKHOLM, SWEDEN. Electrical cardioversion is often used in an attempt to convert persistent afibbers to normal sinus rhythm (NSR). Unfortunately, the relapse rate is high and even with the use of class I or class III antiarrhythmic drugs, only about 50% of electro-cardioverted patients remain in NSR for 6 months or longer.

Researchers at the Karolinska Institute now report that pretreatment with the beta-blocker metoprolol (time-release version, Toprol XL) significantly improves the success rate for cardioversion. Their study involved 168 persistent afibbers who were randomized to receive metoprolol or a placebo starting at least a week prior to cardioversion (NOTE: only about 15% of the study participants were lone afibbers). On average, the participants were on metoprolol or placebo for 28 days prior to cardioversion and they were also prescribed warfarin (INR 2.1 – 3.0) for at least 3 weeks before and 6 weeks after cardioversion. The starting dose of metoprolol was 50 mg/day with a 50 mg stepwise increase to a target dose of 200 mg once a day.

The participants were checked with an ECG 2 hours after cardioversion and then every week for 6 weeks, and then 3 and 6 months after cardioversion. During the first 6 weeks, 49% in the metoprolol group and 47% in the placebo group developed afib again and were given a second cardioversion. At the 6-month checkup, 46% of patients in the metoprolol group were still in NSR as compared to only 26% in the placebo group. It is also of interest to note that while 8% of placebo group members relapsed into afib within 2 hours of their first cardioversion, none of the patients in the metoprolol group did.

Nergardh, AK, et al. Maintenance of sinus rhythm with metoprolol CR initiated before cardioversion and repeated cardioversion of atrial fibrillation. European Heart Journal, Vol. 28, 2007, pp. 1351-57

Editor's comment: It is likely that the metoprolol pretreatment would be beneficial for adrenergic and perhaps mixed afibbers, but it is not at all clear that it would benefit vagal, persistent afibbers. Researchers at the Mayo Clinic have reported that a high blood level of C-reactive protein (CRP), a marker of systemic inflammation, prior to cardioversion is associated with a greater probability of afib recurrence within one month. There is also evidence that a low level of potassium is associated with poorer outcome of cardioversion. Thus, combating inflammation with Moducare or beta-sitosterol, and supplementing with potassium and magnesium prior to cardioversion may improve both the short- and long-term outcome of the procedure.