Three-dimensional mapping of cardiac arrhythmias: what do the colors really mean?

Catheter mapping and ablation are increasingly performed for complex arrhythmias that require a complete understanding of mapping techniques to identify the arrhythmia substrate. In this session of Teaching Rounds, we begin a 3-part series that focuses on key issues related to 3-dimensional electroanatomic mapping. The general principles, rationale, and working of the various mapping systems have been explained well in the existing literature.1–4 In brief, these systems use an electromagnetic or impedance-based catheter location method that allows creation of a 3D anatomic shell of the cardiac chamber of interest. During mapping, the electrogram obtained at a given site is stored and the activation time catalogued as compared with some selected electric signal preference. The accrued points in the map are assigned to an isochronal color scale based on their respective activation times. In addition to the activation map, maps that display the voltage of the recorded electrograms can be created. For successful interpretation of these maps, a variety of considerations must be understood and meticulously managed. Good catheter contact, correct interpretation of the colors in the map, appropriate choice of reference electrogram, complete mapping of the correct chamber of interest, and strategies to address catheter tip migration with respiration or change in cardiac rhythm and annotation of complex intracardiac signals are all examples of such requisites for success.5–8