How to Minimize Atrial Fibrillation after Electrical Cardioversion

Analysis of more than 5,000 successful electrical cardioversions performed without anticoagulation suggests that patients and doctors must act fast to minimize the chances that acute atrial fibrillation (AF) will lead to thromboembolic events.

Existing guidelines recommend that the heart should be shocked back into rhythm no more than 48 hours after the outset of symptoms. New research from Finland, which just appeared in the Journal of theAmerican Medical Association, reportsthat the actual window for optimal outcomes is closer to 12 hours.

The study team pulled records from three medical centers in Finland, including every case that provided clear information about 30-day outcomes and the time that elapsed between disease onset and successful treatment.

Overall, the records showed, 31 patients had strokes within one month of cardioversion and another 7 developed blood clots. The authors noted the events were all documented by imaging, surgery, or autopsy.

Patients who endured less than 12 hours of AF before treatment, however, fared much better than patients whose hearts beat irregularly for 12. That was also true of patients whose hearts beat irregularly for to 24 hours or 24 to 48 hours. The event rate for the first group was just 0.3%, while the event rate for the second two groups was 1.1%.

The study team calculated adjusted odds ratios (OR) and found that people in the 12-24 hour group were 4times as likely to suffer a thromboembolic event as those in the under-12 hour group (95% confidence interval [CI], 1.7-9.1; P = .001) and that those in the 24-48 hour group were 3.3 times as likely to suffer an event than those in the under-12 hour group (95% CI, 1.3-8.9; P = .002).

That same analysis identified several other factors that were significantly associated with greater risk of thromboembolic events: advanced age (OR=1.06; 95% CI, 1.03-1.09 per year), being female (OR=2.1; 95% CI, 1.1-4.3), heart failure (OR=3.5; 95% CI, 1.4-8.6) and diabetes (OR=2.7; 95% CI, 1.3-5.8).

The authors noted that although 48 hours has long been considered the “safe window” for performing cardioversion without anticoagulation, few previous studies had ever investigated the optimal timing for such procedures.

They also wrote that the 0.3% rate of thromboembolic events they found for cardioversions performed within the 12-hour window without anticoagulation compared favorably to the 0.3% to 0.8% risk of stroke found by studies of cardioversion performed after three weeks of anticoagulation.

Reported limitations to the study included the impossibility of verifying patient statements about exactly when they began to experience their irregular heartbeat. Still, the study authors concluded, the patient numbers involved and the size of the detected event suggest a robust and significant finding.

The practical impact of that finding, however, remains uncertain. The delay between the onset of AF and the restoration of heart rhythm typically hinges more upon the time it takes a patient to seek care than the time it takes physicians to treat a patient who presents with AF.

Still, the results from Finland do suggest that emergency department doctors must treat acute AF as quickly as possible rather than allowing afflicted patients to wait as long as 48 hours.