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Arrhythmia termination using Global Optogenetic Stimulation in ChR2 mice hearts

Raul Alejandro Quinonez Uribe
Doctoral thesis
Date of Examination: 2020-08-27
Date of issue: 2021-03-04
Advisor: Luther, Stefan Prof. Dr.
Referee: Luther, Stefan Prof. Dr.
Referee: Fiala, André Prof. Dr.

Persistent Address: http://hdl.handle.net/21.11130/00-1735-0000-0005-1593-D

 

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Abstract

English

Cardiac arrhythmias represent a health threat worldwide that can end in sudden death. Treatments which include electrical shocks, anti-arrhythmic drugs and ablation show various disadvantages such as discomfort for the patients, side and pro-arrhythmic effects as well as lack of specificity. Moreover, arrhythmias display complex spatio-temporal behaviors making their study a challenging task. Cardiac optogenetics is an emerging field used to enable photo-control of cardiomyocytes by inscribing in them light-sensitive ion channels such as Channelrhodopsin-2 (ChR-2). Optogenetic stimulation offers a new dimension to investigate cardiac electrophysiology, from high spatial and temporal resolution to cell specificity and intensity dependent effects. Previous studies have shown the capability of arrhythmia control and termination using optogenetics in ChR-2 transgenic mice hearts. However, these studies relied on local stimulation, which requires either high intensities or long pulses. In this doctoral thesis I seek to investigate the advantages of globally illuminating the heart as a method of optogenetic cardioversion. In order to do so, I first characterized the attenuation of light by the cardiac tissue as well as the response to light stimulation of our model of ChR-2 transgenic mice hearts using the Langendorff-perfusion technique. The effect of the intensity, pulse width and diameter of the fiber under different experimental conditions involving tyrode, blebbistatin and the voltage sensitive dye Di-4-ANBDQPQ were investigated in this first step. Next, I designed an experimental setup that allowed global illumination of the isolated heart. Arrhythmia induction was facilitated using the drug pinacidil before stimulating the hearts using pulses of varying intensities and lengths. I also analyzed the efficiency of optogenetic cardioversion to different arrhythmia wave morphologies, and lastly investigated the time it takes an arrhythmia to be terminated using light in order to better understand the mechanisms behind this phenomenon. My results show that both intensity as well as the length of the pulse affect every aspect of optogenetic stimulation. With a higher effect from intensity, increasing these parameters leads to a higher success in pacing and cardioversion and shortens the time required to terminate an arrhythmia. Furthermore, optical mapping analysis allowed the visualization of spatio-temporal electrical waves on the heart surface. It could be shown that most arrhythmias were terminated by light stimulation of the excitable gap which caused the collision of the arrhythmic wave. The results obtained improve the understanding of optogenetic cardioversion from different perspectives and offer a head start in the design of experiments using large animal models with aims on a future clinical translation.
Keywords: optogenetics; arrhythmia; cardioversion; defibrillation
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