The role of vagal stimulation on atrial arrhythmogenesis

Atrial fibrillation remains poorly understood. despite being the most common form of cardiac arrhythmia. Two differing views exist as to the nature of the underlying activity sustaining atrial fibrillation: (1) Moe´s multiple wavelet hypothesis suggests that multiple meandering wavefronts exist which continuously fractionate and collide, while (2) Lewis´s mother wavelet hypothesis posits a stable circuit off of which break unstable daughter wavelets. Vagal stimulation converts flutter into fibrillation by reducing action potential duration (APD) but does so in a spatially nonuniform way. This study uses a morphologically realistic computer representation of the atria to examine reentrant activity resulting from vagal stimulation of a flutter circuit. Effects of vagal stimulation were incorporated by introducing islands of reduced APD which were varied in number, size and extent of APD reduction. With uniform APD, reentry was not inducible in the right atrium for the stimulation region chosen. Decreasing the APD in the islands increased the chance of inducing reentry with the premature stimulus. In the left atrium, reentry was initiated by an ectopic beat.