Chris O'Shea

Doctoral Researcher
Physical Sciences for Health CDT

Thesis project - "Developing a high-resolution optical mapping setup with integrated high-throughput analysis capabilities for dissecting molecular mechanisms of cardiac arrhythmias"

Supervisors: Dr D Pavlovic, Institute of Cardiovascular Sciences
Dr L Fabritz, Institute of Cardiovascular Sciences
Dr K Rajpoot, School of Computer Science
Dr R Neely, School of Chemistry

Industrial Partner: Cairn Research

Cardiac arrhythmias can result from defective ion handling and electrical conduction slowing within the heart. Better understanding of molecular mechanisms leading to these irregularities in ion handling patterns is required to develop novel antiarrhythmic therapies. Optical mapping utilises potentiometric or ion-specific fluorescent dyes to allow detailed study of cardiac electrophysiology (EP) in intact cardiac tissue. Progress in optical mapping experimentation however is currently hindered by limitations with respect to data acquisition and processing. These include low signal to noise ratios (SNR), ineffective tissue illumination, cardiac motion artefacts, suboptimal spatio-temporal resolution and computational processing challenges associated with large and often noisy data. The work proposed here will build upon previous optical mapping developments to produce a system which combines improved data acquisition abilities, such as improved SNR and spatio-temporal resolution, with integrated processing capabilities. This will aid uncovering of novel molecular mechanisms driving cardiac arrhythmias.

This project proposes to achieve these aims by inter-disciplinary contribution and collaboration from physical, computer, and biological sciences. To improve SNR and spatio-temporal resolution new illuminators will be developed, tested and characterised in collaboration with industrial partner (Cairn Research). These novel illuminators will combine ultra-high stability, fast digital modulation (microseconds), high optical power (>1W at relevant wavelengths), efficient thermal management and homogenous macroscopic field illumination of intact tissue. This work will also extend to custom optics dedicated to macro imaging of intact tissue. LED pulsing to reduce photobleaching and phototoxicity will also be tested in this project, as will the dynamic range and effectiveness of available fluorescent dyes.

The integration of data processing and analysis capabilities within the proposed setup will require development of novel algorithms for calculating key EP parameters in a contracting and non-contracting cardiac tissue. This will include image processing such as thresholding, methods for calculating conduction velocity and techniques for studying arrhythmic data such as phase mapping. This will involve development and implementation of algorithms novel to optical mapping followed by testing on experimental data. Equally the use of chemical contraction uncouplers, which can modify metabolic state of the heart, will be circumvented by computational approaches to account for motion artefacts. One such approach will be to investigate the effectiveness of techniques such as image registration, spatially matching consecutive image frames of contracting tissue, against established models for studying cardiac EP.

The improved system will be used to generate novel mechanistic insights into pathogenesis of atrial and ventricular arrhythmias. Specifically, we will examine how cardiotonic steroids such as ouabain and marinobufagenin affect action potential conduction, morphology and calcium ion handling. We will also examine the effects of drugs, e.g. digoxin, on the effects of these cardiotonic steroids on cardiac conduction, action potential morphology, calcium cycling and ultimately development of arrhythmias. Furthermore, we will investigate the role of genetic factors in arrhythmia development like ion channel mutations, desmosomal proteins and transcription factors. Thus, computational and physical advances developed in this project will allow for a greater understanding of mechanisms leading to development of cardiac arrhythmias.

This project will develop greater understanding of cardiac EP, optical mapping, data processing, algorithm development and characterising, testing and developing novel illuminators and optics, as well as the use of animal models to decipher mechanisms of atrial fibrillation development.