Dr.-Ing. Gunnar Seemann

Mathias Wilhelms

The autonomous activity of the heart is caused by a small, but complex part of the right atrium,
the sinus node (SN). Here, specialized cells permanently effect an electrical excitation of the sur-
rounding tissue in a sinus rhythm. From this primary pacemaker the action potentials propagate
over the atria and via the atrioventricular node to the ventricles, where the main contraction of
the heart actually takes place.
The sinus node is a heterogeneous structure, i.e. there is a difference between center and periphery
regarding cell morphology, electrophysiology and electrical coupling. In contrast, the behavior of
the whole SN differs from that of single central and peripheral cells. Investigating the reasons for
this phenomenon experimentally is very diffcult. Therefore, realistic computer models are helpful
to understand the electrophysiological mechanisms.
In the past, different attempts were made considering sinus node heterogeneity. One possible de-
scription of the electrical conduction is the mosaic model, in which the density of two discrete cell
types is varied from the center to the periphery. Another approach for this task is the gradient
model, in which, as the name implies, a gradual transition is between the center and periphery.
Without a satisfactory description of the sinus node it is difficult to delineate the activity of the
whole heart which builds on these results. These further investigations will help to better under-
stand and describe the processes concerning generation and propagation of electrical excitation.
Diagnosis and treatment of dysfunction of the heart will also be improved by this.

The ob jective of this work is to benchmark different electrophysiological models of the sinus node
to determine the closest approach to reality. For this purpose, a preliminarily chosen cell model is
used for the implementation of the various geometrical models of the SN. The simulated results
are then compared with experimental data.