Larval zebrafish electrocardiography electrodynmaic modelling and sensor design

This thesis presents the first model of the electrical activity of the larval zebrafish heart as well as the design and fabrication of novel electrode arrays that were created to measure the electrocardiogram. The model consists of realistic 3D geometry of a 3 day’s post fertilisation zebrafish heart and body with a bidomain electrical model that uses the Fitzhugh-Nagumo equations as the ionic model. The model is able to replicate experimentally observed conduction velocities and action potentials by using region specific parameters and simulate electrocardiograms that are comparable to measurements. The electrode arrays are constructed from flexible polyimide films with gold microelectrodes. These devices have the potential to improve the measurement of the electrocardiogram for drug screening applications as an alternative to the use of micropipette electrodes. Gold plating and PEDOT:PSS coating techniques were applied to the devices to successfully reduce electrode impedance with the effectiveness of each technique categorised using impedance spectroscopy. The devices were tested $in$ $vivo$ with larval zebrafish with limited success and so $in$ $vitro$ tests were conducted using an artificial current source

3D finite element electrical model of larval zebrafish ECG signals

Assessment of heart function in zebrafish larvae using electrocardiography (ECG) is a potentially useful tool in developing cardiac treatments and the assessment of drug therapies. In order to better understand how a measured ECG waveform is related to the structure of the heart, its position within the larva and the position of the electrodes, a 3D model of a 3 days post fertilisation (dpf) larval zebrafish was developed to simulate cardiac electrical activity and investigate the voltage distribution throughout the body. The geometry consisted of two main components; the zebrafish body was modelled as a homogeneous volume, while the heart was split into five distinct regions (sinoatrial region, atrial wall, atrioventricular band, ventricular wall and heart chambers). Similarly, the electrical model consisted of two parts with the body described by Laplace’s equation and the heart using a bidomain ionic model based upon the Fitzhugh-Nagumo equations. Each region of the heart was differentiated by action potential (AP) parameters and activation wave conduction velocities, which were fitted and scaled based on previously published experimental results. ECG measurements in vivo at different electrode recording positions were then compared to the model results. The model was able to simulate action potentials, wave propagation and all the major features (P wave, R wave, T wave) of the ECG, as well as polarity of the peaks observed at each position. This model was based upon our current understanding of the structure of the normal zebrafish larval heart. Further development would enable us to incorporate features associated with the diseased heart and hence assist in the interpretation of larval zebrafish ECGs in these conditions

Model ECG at different positions with overlaid action potentials.

<p>A) atrial position, B) middle position, C) ventricular position. Red dots mark the key stages in each ECG (P, R and T waves). Atrial repolarisation is also marked (AR, green circle). No voltage scale is shown as the action potentials were scaled so that the ECG was visible on the same axes.</p

Final parameter values used within the model.

<p>Final parameter values used within the model.</p

Comparison between model and recorded action potential properties.

<p>Comparison between model and recorded action potential properties.</p

A comparison between model relative peak heights and measured relative peak heights.

<p>A comparison between model relative peak heights and measured relative peak heights.</p

Comparison between recorded action potentials [9] from a 2 dpf heart and model action potentials.

<p>A) atrium B) atrioventricular band C) ventricle. Action potentials were recorded from explanted 2 dpf hearts at room temperature using patch pipettes and current clamp techniques.</p

Comparison between ECG recordings and model ECG.

<p>The recorded ECG at three positions was compared to the model output. A) model comparison to atrial recording, B) model comparison to middle recording and C) model comparison to ventricular recording. Model 1 has fitted action potential durations, model 2 has a reduced action potential duration that gives a similar QT length to the recordings. No voltage scale is shown as the model ECG voltages are much smaller than the recordings.</p

Conductivity values used within the model for each heart region.

<p>Conductivity values used within the model for each heart region.</p

Activation wave conduction velocities in an adult human and a 3 dpf zebrafish heart.

<p>Activation wave conduction velocities in an adult human and a 3 dpf zebrafish heart.</p