Intermittent Complexity Fluctuations during Ventricular Fibrillation

by Alexander Schlemmer
Doctoral thesis
Date of Examination:2017-03-16
Date of issue:2018-01-31
Advisor:Prof. Dr. Ulrich Parlitz
Referee:Prof. Dr. Ulrich Parlitz
Referee:Prof. Dr. Florentin Wörgötter
Persistent Address: http://dx.doi.org/10.53846/goediss-6706

 

 

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Abstract

English

Ventricular fibrillation is a lethal cardiac arrhythmia that is one of the major causes of death worldwide. A prevalent treatment is the application of a high-energy shock using a cardiac defibrillator. These defibrillation shocks can cause severe pain and might injure the cardiac tissue further, leading to an increased risk for future cardiac arrhythmias. Understanding the mechanisms leading to and sustaining lethal arrhythmias can help to develop improved defibrillation methods. The research questions of this thesis focus on the investigation of complexity fluctuations in the electrocardiogram during ventricular fibrillation and their relation to the spatiotemporal dynamics of electrical excitation waves that drive the contraction of the heart. Using experimental data employing optical mapping and data from cardiac simulations these complexity fluctuations are quantified and characterized using different complexity measures. It is found that periods of low complexity in the ECG can be associated with more organized states with a low number of scroll waves in simulated excitable media. The application of an experimental protocol using low energy shocks targeted at periods of specific complexity in ex vivo experiments using rabbit and pig hearts is presented. While a significant advantage when pacing into low complexity regimes could not be found, one possible reason for this result could be identified: Using multi electrode electrocardiogram data from cardiac simulations it was revealed that there can be a strong dependency of the measurements of complexity fluctuations on the angle of observation. By analysing the surface activity on the simulated heart details about the mechanism behind this heterogeneity were identified. Furthermore, the relation between the spatiotemporal complexity and the complexity observed by external electrodes is quantified for different numbers of electrodes. The implications for the development of angle-resolved measurement devices for complexity are analysed and discussed and provide the basis for future multi-channel complexity measurements.
Keywords: Heart; Arrhythmia; Ventricular Fibrillation; Defibrillation; Complexity
 
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