Signal-averaged electrocardiograms in patients with atrial fibrillation or flutter.

The signal-averaged QRS complex that is prolonged because of low amplitude late potentials predicts ventricular tachycardia. This study investigated if signal-averaged low amplitude atrial potentials predict atrial fibrillation or flutter (AFF). Low amplitude potentials were considered to be high-frequency, high amplitude P (HiFP) duration recorded between 50 and 250 Hz at 1.0 mm/microV amplitude minus unfiltered P (UnFP) duration at 0.1 mm/microV. In nine normals, HiFP averaged 115.6 msec +/- 9.8 SD. HiFP were wider in 26 control patients (133.5 msec +/- 15.7, p less than 0.005) but HiFP-UnFP (11.2 msec +/- 8.5) and signals less than 10 microV terminating HiFP inscription (21.7 msec +/- 23.4) were similar to normal values. Seventeen patients with paroxysmal or recently cardioverted AFF did not have significantly longer intervals than controls (HiFP averaged 138.8 msec +/- 23.0, HiFP-UnFP 13.2 msec +/- 9.3, and signals less than 10 microV 32.4 msec +/- 19.5). Therefore, signal-averaged P waves do not identify patients with AFF.