Characteristics of intracardiac electrograms II: Atrial endocardial electrograms.

The intra-atrial electrograms (P-wave and QRS complex) of newly implanted electrodes were recorded, and the time and frequency domain characteristics compared. The sensing impedance properties of the atrial electrode were studied in relation to the characteristics of both atrial and ventricular electrograms, and specific differences between the P and R-waves were identified. These values, particularly the amplitude and frequency components, were sufficiently distinct to make differentiation by pacemaker sensing circuits selective and reliable.