[A method of determining the location of the pacemaker in the canine right atrium]

Theoretical calculations and experiments on hearts of open-chest dogs have demonstrated a possibility of localizing a spontaneous excitation focus by recording 2 intra-atrial delays representing differences in activation moments at 3 sites of the right atrium. Assuming myocardial homogeneity with respect to excitation spread velocity, it has been shown that the pacemaker can be localized by intersection of two hyperbola-like intra-atrial delay isochronisms with recording electrodes at their foci. In natural, i.e. nonhomogeneous myocardium, experiments have been conducted to simulate pacemakers with known co-ordinates by electrical stimulation of various sites within the right atrium. Comparison of experimental and theoretical data showed the present method to be able to localize the pacemaker with an error of +/- 3 mm, provided the pacemaker is between the recording electrodes where the intra-atrial delays do not exceed 60% of their maximum values.