Background The relation between abnormalities in the signal-averaged P wave and atrial size has not been determined in patients with paroxysmal atrial fibrillation (PAF) without structural heart disease. Methods Signal-averaged electrocardiograms of P waves were recorded in 38 patients with idiopathic PAF and 34 control subjects. Filtered P wave duration (FPD) and root-mean-square voltages for the last 20 ms of the vector magnitude were measured. Atrial volume was calculated by cine magnetic resonance imaging. Results FPD was longer (131.7 +/- 10.9 ms vs 120.8 +/- 8.6 ms, P < .0001) and roof-mean-square voltage was lower (2.89 +/- 1.29 mu V vs 3.62 +/- 1.48 mu V, P < .05) in the PAF group than in control subjects. However, the various atrial volumes were similar in the 2 groups. in controls, FPD was significantly correlated with left (r = 0.593, P < .0001) and total (r = 0.492, P < .005) atrial volume but not with right atrial volume, in patients with PAF, no significant correlations were found between FPD and any of the atrial volumes. Elderly patients with PAF (age greater than or equal to 60 years) showed longer FPD than younger patients with PAF (139.2 +/- 9.4 ms vs 125.6 +/- 8.0 ms, P < .0001). Conclusions FPD is influenced by the left and total atrial volumes in the normal heart without PAF. Prolonged FPD seems to be a useful predictor of idiopathic PAF among patients without atrial enlargement, especially in the elderly.
