| dc.description.abstracteng | The heart is an excitable medium which supports the propagation of waves of electrical excitation.
While these excitation waves enable the normal functioning of the heart,
they also allow for self-sustained arrhythmic activity.
Such self-sustained spiral wave activity underlies life-threatening cardiac arrhythmias such as ventricular fibrillation,
and has to be treated with high-energy electrical shocks.
However, electrical defibrillation may have severe side effects,
including tissue damage and intolerable pain.
Therefore, improving cardiac defibrillation is an important aim
and requires a sound understanding of the mechanisms underlying
the dynamics of fibrillation.
This thesis focuses on the experimental characterization of the spatio-temporal
dynamics and its control during ventricular fibrillation in Langendorff-perfused rabbit hearts.
One aspect of the heart tissue is that its dynamical properties may change
over time or be spatially heterogeneous.
For example, ischemia due to reduced flow of blood affects spatial-temporal dynamics
on the organ level as well as spatially localized variations of the tissue properties.
In the first part of this thesis, the emphasis is on the characterization of the dynamics of ventricular
fibrillation and in particular the dynamics of phase singularities at the core of the
spiral waves.
To achieve this goal for the optical mapping data, a novel approach for phase singularity identification and
tracking is introduced.
This method is applied to a pharmacological model of ischemia in the rabbit heart using Pinacidil.
It is used to study the effect on spatial-temporal activation dynamics of ventricular fibrillation.
Furthermore, the temporal fluctuations of the number of phase
singularities observed on the heart surface is then investigated using a stochastic
Markov model approach.
We show that the Markov model captures essential properties and dynamics of
phase singularities during ventricular fibrillation.
The second part of the thesis studies the effect of spatial heterogeneity
on fibrillatory dynamics.
Using numerical simulations we investigate the interaction of phase singularities
with heterogeneities and provide experimental observations of similar dynamical
phenomena in the heart.
The third part then analyzes how electrical shocks exert control
on the ventricular fibrillation.
The effect of a shock depends on its timing, and here
a statistical approach is used to visualize and quantify its control.
In summary, this thesis introduces and applies new methods to allow a more
detailed characterization of the dynamics during ventricular fibrillation and
its interaction with electrical shocks. | de |