Locating ectopic foci

Locating Ectopic Loci. introduction: Successful radiofrequency ablation of an ectopic focus requires accurate localization of the region of enhanced automaticity. Present localization techniques require detailed electrical mapping that is time-consuming and involves much trial and error. Here, we propose two new localization techniques which were used to locate a pacemaker in a computer simulation, Methods and Results: We suggest that an ectopic focus can be located by measuring the activation sequence of three or more intracardiac electrodes subsequent to an ectopic depolarization. Furthermore, the resetting response of an ectopic pacemaker can be used to estimate the distance from the stimulation electrode to the ectopic focus. We derive simple geometric localization strategies based on these ideas and examine the sensitivity of the strategies with respect to measurement uncertainties and electrode arrangements. Our localization strategies were tested using a numerical simulation of a pacemaker in a sheet of excitable media described by modified FitzHugh-Nagumo equations. The strategy based on electrode activation sequences located the pacemaker region in a homogeneous isotropic sheet after an average of 2.2 +/- 0.8 iterates In 10 out of 10 trials starting from random initial catheter positions. In the case of an inhomogeneous anisotropic sheet, the pacemaker was located after an average of 4 +/- 3 iterates in 9 out of 10 trials. The localization strategy based on resetting successfully found the pacemaker in a homogeneous isotropic sheet after an average of 1.2 +/- 0.4 iterates in 5 out of 5 trials and localized the pacemaker in an inhomogeneous anisotropic sheet after an average of 1.4 +/- 0.5 iterates in 5 out of 5 trials. Conclusions: Simple geometric strategies can be used to locate an ectopic focus, Although our basic localization strategies are sensitive to the electrode arrangement and measurement uncertainties, we show that iteration of our techniques quickly locates the pacemaker.