Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Physiology

Supervisor

Dr. Doug Jones

Abstract

Arrhythmia mechanisms rely on multiple factors including structural (myogenic), nervous (neurogenic), and interrelated (the neuro-myogenic interface) factors. I hypothesized that due to this neuro-myogenic interface, the intrinsic cardiac autonomic nervous system (ICANS) is involved in most atrial arrhythmias. This thesis also provides a "Threshold Model" as a tool to assess the role of different physiological factors influencing arrhythmia. This model allows relative comparison and interpretation of the role of various factors influencing arrhythmogenesis. The mouse allows relatively simple manipulation of genes to determine their role in arrhythmia. This thesis determined what atrial arrhythmias are inducible in the mouse (in vivo) and how to systematically study those arrhythmias. I found that atrial tachycardia/fibrillation (AT/F) and junctional tachycardia (JT) are inducible in the mouse. AF and JT pose significant clinical challenges as many patients do not respond well to current interventions. Neurogenic AF relies on acetylcholine, while myogenic AF relies, in part on gap junctions formed by connexins (Cxs). The atria has muscarinic M2 and M3 receptors. The duration of M2R/M3R G protein signalling is regulated by GTP hydrolysis, a process accelerated by the regulators of G protein signalling (RGS). RGS2 deficient (RGS2-/-) mice had reduced refractory periods that were normalized with a selective M3R blocker (Darifenacin) and increased susceptibility to AT/F induction compared to littermates. For the first time, this showed a role of M3 and RGS in atrial arrhythmia. Cx40 deficient (Cx40-/-) mice were protected from carbachol induced AT/F, while Cx43 G60S mutant (Cx43G60S/+) mice, with an 80% reduction in phospho-Cx43 in the atria were highly susceptible to AT/F that was terminated by darifenacin. This shows a novel neurogenic component to what was previously described as myogenic arrhythmia. Another novel finding was that JT has a neurogenic component, resulting from inappropriate AV nodal pacemaker activation initiated by autonomics. Ivabradine hydrochloride, a selective pacemaker channel blocker, prevented JT and may be useful in patients with JT.

In conclusion, this thesis has provided novel findings of the vital role of the neuro-myogenic interface in atrial arrhythmias and has provided the basis for future investigations of potential therapeutic options for patients.

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