An integral equation model for intracardiac electrogram sensing

The electrogram sensed by an intracardiac electrode has long been characterized based on two approaches: (1) presuming that the electrode is very small and does not disturb the potential prior to applying the electrode; and (2) taking an average of the prior potential over the electrode surface. In fact, any intracardiac sensing electrode has a finite surface area where electrical charges are induced and disturb the external potential field, thus, the sensed potential is different from the potential prior to placing the electrode. In this paper, an integral equation model is proposed based on the current continuity equation in a homogeneous myocardial medium. The new model can accurately characterize the electrogram sensed by an electrode with a nonnegligible surface area and a load impedance. The new model can be solved numerically via the method of moments to obtain the potential induced on the electrode surface by an arbitrary dipole volume source. As an application of the proposed theory, several electrode configurations with different loads have been analyzed with an intent to show that a finite electrode surface will significantly reduce the electrogram peak amplitude and slope, and a load impedance lower than 20 kΩ will also degrade the electrogram sensitivity.