Ectopic and reentrant activation patterns in the posterior left atrium during stretch-related atrial fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in humans and is predicted to dramatically increase its prevalence in the future. There is experimental evidence that increasing stretch increases the dominance of the pulmonary veins (PVs) during AF in isolated hearts and ectopic activity in the isolated PVs, but the ionic mechanisms underlying such effects are not clear and the ability of the PVs to favorably host functional reentry during stretch cannot be excluded. We used a combination of endocardial-epicardial optical mapping with phase and spectral analysis to study stretch-related AF (SRAF) in normal isolated sheep hearts. We have found rapid AF sources in the posterior left atrium (PLA) and PV region and their activation frequency and level of organization correlated with intra-atrial pressure. Analysis of the surfaces' optical mapping data in the phase domain reveals that activation of the PLA consisted of alternating patterns of breakthroughs, reentries and relatively simple waves swiping across the mapped field. The patterns on the endocardial and epicardial PLA surface at any given moment of time of the SRAF could be either identical or not identical, and the activity in the thickness of the PLA wall is hypothesized to conform to either ectopic discharge or scroll waves, but a definite evidence for the presence of such mechanisms is currently lacking. Thus the understanding of the manner by which the mechano-electric feedback effects in the PLA, including the PVs, become important in the initiation and maintenance of AF requires further detailed investigation.