Far-field effect in unipolar electrograms recorded from epicardial and endocardial surface: Quantification of epi-endo dissociation during atrial Fibrillation in Humans

In this study we explore whether endo-epicardial dissociation during atrial fibrillation (AF) can explain origin of some of the far-field components in unipolar electrograms. To assess the number of far-field deflections in unipolar electrograms that have a source on the contralateral side of the atrial wall we used simultaneous endo-epicardial high-resolution contact mapping. 30s endo-epicardial electrograms were recorded using two 64 electrode arrays directly opposing each other, placed on the right atrial wall in 5 patients with persistent AF. For all far-field deflections that could not be explained by local activation within the same plane, we searched for a passing wavefront on the other side of the atrial wall. 74±3% of detected far-field deflections could be explained by activation on the same side of the atrial wall. Within the remaining deflections, 42±5% had a source in the activity taking place directly on the other side of the atrial wall. 15±3% of all detected far-fields were of unknown origin. High proportion of the far-field deflections detected using contact mapping during AF results from endo-epicardial dissociation may have an impact on proper annotation of local activity, and therefore on identification of conduction patterns. Calculating the number of far-field deflections in unipolar electrograms due to endo-epi dissociation may help to quantitatively describe transmural dissociation.