Teaching Points With 3-Dimensional Mapping of Cardiac Arrhythmias

Abstract

Before creating a detailed 3-dimensional map of an arrhythmia, the electrophysiologist should already have a reasonable idea regarding which cardiac chamber contains either the focal site of origin of an automatic tachycardia or the relevant substrate for reentry. Typically, a combination of careful review of the ECG during tachycardia and knowledge of the location of abnormal substrate (such as myocardial infarction, atriotomy scar, etc) will allow focused mapping in the appropriate chamber. Prior teaching points have already discussed1,2 the fact that an isolated “early site of activation” is essentially meaningless for guiding ablation of macroreentry. However, in some circumstances, even for a focal “automatic” tachycardia, the apparently early site is not a suitable site to target for ablation. After constructing the activation map during tachycardia before ablation, especially if the earliest site of activation obtained does not appear to be particularly early compared with the surface ECG reference, the following should be considered. ### Overlapping Cardiac Structures Mapping a chamber other than the actual chamber where the tachycardia originates will clearly lead to a wrong conclusion. For example, when mapping premature ventricular tachycardias or monomorphic ventricular tachycardia in a structurally normal heart, a detailed map of the right ventricular outflow tract may show the “earliest site” of activation to be in the posterior wall of the right ventricular outflow tract. The true site of origin may, however, be in a coronary cusp or the subvalvar anterior left ventricular outflow tract. The posterior right ventricular outflow tract may appear to be early because a far-field signal is detected on the mapping electrode or because of breakthrough in the right ventricular outflow tract from the wave front originating on the other side of the region.3,4 After mapping the left ventricle and coronary cusps and combining the maps, the earliest activation …