Chronic atrial fibrillation in man. Activation, organisation and characterisation

Abstract: Chronic atrial fibrillation (CAF), with a prevalence progressively increasing with age, is one of the most common cardiac arrhythmias in man and associated with increased morbidity and mortality. Previous studies have shown that, in animals as well as in man, experimental atrial fibrillation is based on different types and dimensions of intra-atrial electrical re-entry. However, there is a lack of data on the electrical phenomena during the chronic type of this arrhythmia. By exploring the activation of the right atrial free wall during open-heart surgery in patients with CAF and an underlying heart disease, we confirmed the previous experimental findings. In addition, areas with organised activation were identified in a majority of the patients. The nature of the organised activation suggested re-entry in an anatomical structure, like the right annular bundle surrounding the tricuspid valve. In patients without signs of organised activation, multiple activation waves continuously re-enter either themselves or each other due to functional properties of the atrial myocardium. However, we failed to demonstrate that anisotropy in conduction velocity was a general property of the epicardial right atrial free wall of the intact human heart, both in patients with stable sinus rhythm and in patients with CAF. For non-invasive characterisation of CAF, we developed and validated a new ECG method for assessment of the magnitude and the dynamics of the atrial fibrillation cycle length. This new method was subsequently used to explore the influence of anaesthesia and heart exposure on atrial refractoriness in patients with CAF. We found that inhomogeneous cooling of the atrial myocardium, anaesthesia and modulation of the autonomic tone increased both the atrial refractory period and the heart rate significantly. These findings suggest that intra-operative data do not represent entirely normal conditions.