Unpinning of a rotating wave in cardiac muscle by an electric field

The possibility of terminating cardiac arrhythmias with electric fields of moderate intensity is a challenging problem from a fundamental point of vie w and an important issue for clinical applications. In an effort to underst and how anatomical re-entries are affected by electric fields, we found tha t a weak shock, with an amplitude of an order of magnitude less than the de fibrillating shock, may unpin the vortices rotating around the defects (obs tacles). The unpinning results from a depolarization of the tissue near the obstacle, induced by an external electric field within a distance of order lambda similar to 1 mm. Unpinning was observed both in the FitzHugh model of excitable tissue, and in a specific Beeler-Reuter model of cardiac tissu e. This theoretical observation suggests that anatomical re-entries can be transformed into functional re-entries, an effect that can be tested in exp eriments with cardiac muscle. (C) 1999 Academic Press.