Teaching Points With 3-Dimensional Mapping of Cardiac Arrhythmias

Abstract

The map obtained of a tachycardia is greatly influenced by how meticulously individual activation points are annotated to indicate the timing of activation. The annotation window is typically set to display surface leads and intracardiac electrograms.1,2 These include the electrogram or ECG lead used as the timing reference as well as the bipolar and unipolar signals from the mapping catheter.3–5 Assuming that the point of reference electrograms remains stable and the window of interest and tachycardia cycle length are unchanged, the consistency of annotating the timing of mapping catheter–derived electrograms is the defining factor for the accuracy of the map. The operator must have a consistent plan as to how to annotate the electrogram timing as well as a method of handling double potentials and fragmented signals. ### Electrogram Annotation Several potential options as to how to annotate the electrogram timing exist, including whether to use unipolar or bipolar signals, taking the maximum amplitude of the electrogram, earliest portion of the electrogram, and so forth. #### Earliest Part of the Electrogram This method is the least desirable approach. The earliest signal may represent far-field activation, and in some instances, especially on the septum or where there are neighboring electrically active structures or in the vicinity of scar/slow conduction, a marked discrepancy between the earliest recorded far-field signal and the timing of actual activation at the site can exist (Figure 1). Although such discrepancy is magnified with unipolar recordings, the problem also exits with standard spaced bipolar recordings. Figure 1. Probably the least accurate method of taking activation points involves simply taking the earliest or start of the bipolar signal. The schematic shows possible findings for assessing activation times on adjacent sides of the septum, with early activation at the right side of the septum. Although this approach may correctly identify the ablation target in some …