Atrial fibrillation substrate mapping with emphasis on voltage-based guidance

Figure 3 To show variability of atrial fibrillation electrograms (patient with persistent atrial fibrillation) the frequency spectrum was first computed for electrograms acquired at dual sites in proximity in the left atrium. Similar values of dominant frequency (DF) are evident (left panels), and it is apparent that the DF in each case is the predominant frequency–only a few lesser frequency components are evident in each spectrum. Addressing this scenario, the time series was windowed based on the period of each DF, with the resulting segments evident in the right panels. The electrogram deflections for each DF cycle are often overlapping. In the top right panel, the electrogram is broad and biphasic, starting with a negative deflection and ending with a positive deflection. Although there is some cycle-to-cycle variability, the gross morphologic properties appear mostly consistent. The same basic shape and pattern are evident in each cycle, except for a few deviations. The deviations include earlier onset of the early deflection, which corresponds to earlier arrival of the wavefront at the negative pole of the bipolar electrode. The abscissa is given as sample number, and for the digitization rate of 1200 Hz it is an approximation of the time in milliseconds. Likewise, for the overlap of the lower right panel electrogram, there is similarity between segments, although the entire biphasic deflection sometimes occurs earlier in the cycle, suggesting earlier breakthrough from the source or earlier completion of the reentrant circuit, with variable degree of earliness. DF: Dominant frequency.