Effect of Bipole Configuration on Atrial Electrograms During Atrial Fibrillation

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Abstract
Despite an increasing body of work on the nature of fibrillatory rhythms, and the application of different bipole configurations in antifibrillatory devices, little published work has assessed the effect of bipole configuration on the endocardial recordings of fibrillatory rhythms. To address this issue, a specially designed 6 Fr decapolar catheter was used to record intra‐atrial electrograms during sustained atrial fibrillation in 15 patients. Simultaneous filtered (30–500 Hz) and unfilfered (0,05–5,000 Hz) recordings of atrial fibrillation were performed of four different bipole configurations: (a) 1‐mm interelectrode spacing adjacent to the atrial wall; (b) 10‐mm interelectrode spacing adjacent to the atrial wall; (c) 10‐mm inter‐electrode spacing 24 mm from the distal catheter tip; (d) 1‐mm interelectrode spacing 24 mm from the distal catheter tip. One minute of such data was recorded, and each 4.27‐second segment (X 14 segments) was analyzed for atrial rate, electrogram amplitude, amplitude probability density function (apdf), median frequency in the 2–9 Hz band, and elecfrogram morphology. Changes in bipole configuration resulted in profound changes in calculated afrial rate, amplitude, and apdf (P < 0.001 by two‐way ANOVA in each instance). Specifically, closer interbipole spacing and closer proximity to the atrial wall resulted in lower calculated atrial rates, higher electrogram amplitudes, and higher apdf values. In contrast, median frequency proved to be a more robust measure despite multiple configurations (P> 0.10 by two‐way ANOVA). These changes significantly affected the predictive value of previously published detection criteria for rate (P < 0.01) and apdf (P < 0.000001). Bipole location also affected morphology, with locations adjacent to the atrial wall and with closer interbipole spacing having more discrete electrograms and greater apparent organization (P < 0.0001). Further, when data segments from all patients and bipole configurations were grouped, rate and apdf were found fo be strongly inversely correlated (r = ‐0.808). In conclusion: (1) Bipole configuration has important effects on calculated atrial rate, electrogram amplitude, and apdf during atrial fibrillation; (2) Median frequency and frequency domain analysis may be a more robust way of characterizing atrial fibrillation despite the use of different bipole configurations; (3) Changes in bipole configuration affect the efficacy of detection criteria, and considerations about the level of organization of a cardiac rhythm; (4) Rate and apdf may be largely redundant measures of fibrillatory rhythms; and (5) Traditional estimates of atrial rates up to 700/min during atrial fibrillation, based on the unipolar or widely spaced bipolar leads of the surface electrocardiogram, reflect the effects of their recording methods. and are an overesfimation of the true atrial rate.