Does atrial fibrillation cause false-positive late potentials?

We hypothesized that atrial fibrillation may cause false-positive late potentials due to the recording of baseline atrial activity. We performed signal-averaged ECGs in 26 patients with atrial fibrillation before and after conversion to normal sinus rhythm. Signal-averaged ECGs were recorded for > 200 cycles with a noise level of < or = 0.5 microV. The signals were band-pass filtered at 40-250 Hz. We examined filtered QRS duration (fQRS), duration of low amplitude signal < 40 microV (LAS), and the root mean square (RMS) of the terminal 40 msec of the QRS complex. A late potential was considered present when two of the following three criteria were met: fQRS > or = 114 msec, LAS > or = 38 msec, and RMS < or = 20 microV. The mean +/- standard deviation of the fQRS in atrial fibrillation and sinus rhythm were 113 +/- 28 and 110 +/- 25 msec; of the LAS 38 +/- 17 and 37 +/- 15 msec; of the RMS 27 +/- 22 and 28 +/- 21 microV; of the noise 0.25 +/- 0.08 and 0.22 +/- 0.07 microV (P = NS). Ten signal-averaged ECGs in atrial fibrillation had late potentials. With reversion to sinus rhythm one of these 26 patients gained a late potential; two others lost a late potential (P = NS by McNemar's Chi-square). There was no significant difference in the signal-averaged ECG parameters or noise levels. In conclusion, signal-averaged ECG parameters are not significantly changed by cardioversion of atrial fibrillation to normal sinus rhythm.(ABSTRACT TRUNCATED AT 250 WORDS)