The signal-averaged electrocardiogram of P wave in patients with documented atrial fibrillation or flutter and in patients with left or right atrial overload without atrial fibrillation.

To evaluate the significance of the signal-averaged P wave in various pathological conditions of the atrium, signal-averaged electrocardiograms and echocardiograms were studied in the following 4 groups: (1) 10 normal subjects (control group), (2) 24 patients with paroxysmal atrial fibrillation or flutter (AF) (AF group), (3) 12 patients with left atrial overload without AF (LA group), and (4) 10 patients with right atrial overload without AF (RA group). Original P wave durations showed no significant difference among the 4 groups. Filtered P wave durations (F-PDs) in the AF and LA groups were significantly longer than that in the control group. F-PD correlated significantly with left atrial dimension (LAD). F-PD in AF patients with LAD shorter than 40 mm was significantly longer than that in the control group, but there was no significant difference in F-PD between AF patients with LAD longer than 40 mm and the LA group. Root mean square voltages of original P waves were significantly higher in the LA and RA groups than that in the control group, but in AF patients it did not differ from that in the control group. In conclusion, the signal-averaged P wave is useful to predict atrial fibrillation, but prolongation of F-PD is seen not only in patients with AF but also in patients with LA overload.