Analysis of the P wave with signal averaging to assess the risk of atrial fibrillation after coronary artery bypass surgery.

P wave signal averaging was performed in 91 consecutive patients undergoing coronary artery bypass grafting to detect patients at risk of postoperative atrial fibrillation (AF). Sixteen patients (17.5%) developed AF after surgery. The P wave duration on the signal-averaged electrocardiogram (ECG) and on surface ECG was prolonged in AF patients compared to others (respectively 141 +/- 12 vs. 132 +/- 12 ms and 124 +/- 9 vs. 113 +/- 9 ms). The root mean square voltages (RMS) of the total P wave were not different between the two groups; the RMS of the late portion of the P wave (late RMS) was significantly higher (0.25 +/- 0.15 vs. 0.17 +/- 0.10 microV) and the RMS of the first 110 ms of the P wave (early RMS) significantly lower (0.88 +/- 0.28 vs. 1.09 +/- 0.33 microV) in AF. The late/ early RMS ratio was different (0.29 +/- 0.16 vs. 0.17 +/- 0.11). In a multivariate analysis only age and the late/early RMS ratio were predictive for AF.