Characterisation of Atrial Electrophysiology with respect to Atrial Fibrillation - A Non-Invasive Approach

Abstract: Atrial fibrillation (AF) is the most common form of cardiac arrhythmia encountered in clinical practice, accounting. Recent findings highlight the need for better characterisation of the arrhythmia in each patient, in order to improve patient treatment. The main objective of this work was to characterise atrial electrophysiology with respect to AF by means of non-invasively obtained data. Spectral analysis of QRST-cancelled ECG recorded during AF was used in Studies I-IV. The derived parameter, atrial fibrillatory rate (AFR), was used as an index of atrial refractoriness. Analysis of signal-averaged P waves was used in Study V when studying patients with hypertrophic cardiomyopathy (HCM) during sinus rhythm (SR). In Study I, patients with permanent AF were investigated using long-term ECG recordings. AFR was estimated once every hour. A lower fibrillatory rate was observed during night-time, indicating that the withdrawal of the sympathetic nervous system is affecting the atria more than the increased parasympathetic tone. In Study II, patients with permanent AF and third degree AV block treated with pacemaker were investigated. Baseline recordings were compared with recordings made during controlled respiration with and without preceding atropine injection. The results demonstrate that the atria are modulated by the parasympathetic nervous system during AF. In Studies III and IV, the possible clinical applications of AFR were investigated. In Study III, the correlation between AFR and parameters obtained from transoesophageal echocardiography was studied. Although a strong correlation was found between AFR and left atrial appendage outflow velocity, the correlation was not strong enough to allow predictions of the latter based on the former. In Study IV, it was found that the AFR in patients relapsing to AF following cardioversion was significantly higher than in patients maintaining SR. In patients with limited arrhythmia duration it is probable that AFR can be used as a clinical predictor of relapse probability. In Study V, it was shown that the interatrial conduction in the AF prone HCM population is different than in a healthy control population. The morphological changes in the P wave appear to be best explained by a higher prevalence of blocking of one or more of the interatrial conduction routes. The present work sheds further light on the characteristics of AF electrophysiology. It is also demonstrated that by applying non-invasive techniques, important information may be obtained that is likely to affect everyday AF treatment.