Organized micro-activity in chronic atrial fibrillation

The mechanisms maintaining chronic atrial fibrillation (AF) are still poorly understood while the number of affected patients is increasing. Recently, rapidly firing foci located mainly in the pulmonary vein ostia were identified as targets which enable a curative inter-ventional treat-ment of AF by radio-frequency (RF) ablation. In most cases a burst of rapidly dis-charging foci triggers the onset of AF, while only in a few cases stable focal activity was identified as the maintaining mechanism of AF. Thus, RF therapy should be most effective in patients with frequent paroxyms of AF. Interestingly, RF ablation is highly effective in patients with chronic AF, too. This outcome suggests that RF delivery in the posterior left atrium has an additional interaction with micro re-entry circuits maintaining the tachycardia. In the past decades it was mainly suspected that irregular propagating re- entrant waves maintain AF (multiple wavelet hypothesis). In con-trast recent findings in the sheep model indicate that a stable micro re-entry circuit using anatomical structures as e.g. the pulmonary vein ostia as anchor points can act as the maintaining mechanism (mother wavelet hypothesis). The project applied for is based on the hypothesis that in a high number of patients such a stable micro-reentrant circuit sustains AF. It should be verified by means of a computer model which parameters (e.g. electrical remodeling, increased anisotropy by aging, enlarged left atrium, fibrous micro structure of venous ostia, etc.) could favor the formation of stable driving micro re-entries. Particular effort will be made for finding a reasonable compromise between necessary detail in the model and computational load. In order to ensure realistic model predictions the comparison with intra-cardiac data is a key link in the project. Invasive studies will be carried out at the University Hospital Innsbruck, Department of Cardiology. Simulated and measured electrograms should be compared by a spectral analysis which has been previously applied in animal and computer models. The application of this technique to humans could enable the identification of stable micro re-entries in individual patients. The effect of RF delivery on the stability of such pathways will be investigated by computer simulation. Currently, procedure times are extremely long and the success rate is small compared with other supraventricular tachycardias. The insight obtained from the performed computer simulations and intra-cardiac measurements should lead to new ablation strategies with shorter procedure times and a higher success rate.