Electrocardiographic features of atrial depolarization during pacing of right atrial appendage

Identification of atrial capture during pacing from right atrial appendage is frequently difficult. Electrocardiograms of forty five patients implanted with AAI/DDD pacemakers (thirty unipolar, fifteen bipolar) were analysed to characterize the specific morphology of paced P waves. Compared to sinus P waves, atrial pacing resulted in atrial depolarization of lower amplitude (0.16 +/- 0.05 mv vs 0.11 +/- 0.032 mv, P less than 0.005) but increased duration (0.07 +/- 0.009 sec vs 0.08 +/- 0.017 sec, P less than 0.005). P wave morphology was similar in unipolar and bipolar pacing units. It was positive in lead I (80%), II (71.11%), III (80%) and aVF (75.55%). In lead aVL, paced P waves were usually diphasic with an initial negative deflection (35.55%). Precordial leads showed paced atrial depolarization of small amplitude and did not help in identification of atrial capture. In unipolar pacing P waves were best seen in lead III because of small pacing spike in this lead. Lead II was suitable for identification of paced P waves in bipolar pacing. Thus careful examination of standard ECG leads for paced P waves of low amplitude, prolonged duration and specific morphology can help in confirming atrial capture following pacing stimulus from right atrial appendage.