Signal-averaged P wave duration predicts early recurrence of atrial fibrillation after cardioversion.

Thirty-two patients had signal-averaged P wave duration measured after electrical cardioversion of AF, and were followed for 1 year or until there was a recurrence. The use of antiarrhythmic medications was left to the discretion of the attending physician. Among 20 patients not taking antiarrhythmic medication, the 11 patients who had a recurrence of AF within 3 months of cardioversion had a significantly longer signal-averaged P wave duration compared to the 9 patients who did not (148 +/- 17 vs 135 +/- 20 ms, P = 0.005). There was no difference in clinical parameters or left atrial diameter. A signal-averaged P wave duration cutoff anywhere between 130 and 135 ms correctly classified 85% of patients with a sensitivity of 81% and a specificity of 89%. In patients taking antiarrhythmic medications, signal-averaged P wave duration did not correlate with the risk of recurrence. In patients not taking antiarrhythmic medications, signal-averaged P wave duration can be used to predict the risk of an early recurrence of AF after cardioversion. The poor predictive value in patients taking antiarrhythmics may be due to changes in the atrial refractory period, which are not reflected in P wave duration.