Permanent biatrial and/or multisite atrial pacing may prevent atrial fibril
lation (AF), but the effects on atrial electrophysiology remain incompletel
y understood. Acute biatrial pacing was studied in 20 patients with and 28
without (controls) a history of atrial fibrillation and/or flutter. Twelve-
lead electrocardiograms were recorded during pacing from the high right atr
ium (RA), from the distal coronary sinus (LA), and biatrial pacing. P wave
duration was measured in each lead and the difference between maximum and m
inimum P duration was termed P wave dispersion. Effective refractory period
s (ERPs) were measured during each pacing mode. The dispersion of P wave du
ration was 35 +/- 14 ms in controls and 40 +/- 29 ms in AF patients (P = 0.
17). Compared to RA pacing, LA pacing shortened P duration in controls (127
+/- 28 to 107 +/- 16 ms, P < 0.05) and biatrial pacing markedly shortened
P duration in controls (127 +/- 28 to 93 +/- 14 ms, P < 0.05) and AF patien
ts (114 +/- 43 to 97 +/- 21 ms, P < 0.05). P wave dispersion rs as unaffect
ed. In controls, the LA ERP was longer than the RA ERP. This phenomenon was
not present in AF patients, whose LA ERP was shorter than that of controls
. Biatrial pacing had no effect on atrial ERPs or the dispersion of atrial
refractoriness. In conclusion, acute biatrial pacing does not affect atrial
repolarization but it does cause a marked shortening of global biatrial de
polarization. Distal coronary sinus pacing produces a shorter P wave than R
A pacing. There is substantial dispersion in the surface P wave of the elec
trocardiogram, the significance of which awaits further study.