  Virtual heart models have been proposed to enhance the safety of implantable
cardiac devices through closed loop validation. To communicate with a virtual
heart, devices have been driven by cardiac signals at specific sites. As a
result, only the action potentials of these sites are sensed. However, the real
device implanted in the heart will sense a complex combination of near and
far-field extracellular potential signals. Therefore many device functions,
such as blanking periods and refractory periods, are designed to handle these
unexpected signals. To represent these signals, we develop an intracardiac
electrogram (IEGM) model as an interface between the virtual heart and the
device. The model can capture not only the local excitation but also far-field
signals and pacing afterpotentials. Moreover, the sensing controller can
specify unipolar or bipolar electrogram (EGM) sensing configurations and
introduce various oversensing and undersensing modes. The simulation results
show that the model is able to reproduce clinically observed sensing problems,
which significantly extends the capabilities of the virtual heart model in the
context of device validation.
