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 discussed 1,2 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. Figure 1. Activation map of a focal tachycardia ablated in the supravalvar pulmonic area. In each map, colors reflect activation time relative to the QRS with earliest activation shown as red; yellow, green, blue, and purple indicate progressively later activation. A, Activation map of the right ventricle (RV) with earliest activation at the left anterior right ventricular outflow tract (RVOT) at Ϫ97 ms before the reference time. B, Activation map of a limited area of the left ventricular outflow tract (LVOT) has been added, showing that earliest activation remains in the RVOT at Ϫ97 ms. C, Activation map of the proximal pulmonary artery (PA) has been added. Earliest activation is now identified in this supravalvar region at Ϫ106 ms. D, Activation map of the aortic root (AO) is added. There is no further change in the earliest activation point, which remains above the pulmonary valve, identifying the successful ablation site.

Three-Dimensional Mapping of Cardiac Arrhythmias

“…When the catheter is manipulated within the heart, the recorded electrograms are combined with the location of the catheter to create activation and/or voltage maps as a 3-D geometric representation. [1][2][3][4][5] In the impedance-based system (NavX), a constant highfrequency and low-level current is emitted between 6 patches that are placed on the skin so as to locate the pair in 3 orthogonal axes (x, y, z), in which 1 patch of each pair acts as a sender of the current, and the other as a receiver. When the fixed electrical current goes through the heart, a voltage shows a linear decrease along its axis between each pair of the patches, depending on the distance from the sender to receiver.…”

How to Approach Reentrant Atrial Tachycardia After Atrial Fibrillation Ablation

“…[15][16][17][18][19] A stimulus that captures the tissue in the excitable gap of the reentrant circuit resets the tachycardia during entrainment pacing. The resulting orthodromic wave front returns to the pacing site after completing one revolution along the circuit.…”

Editor’s Perspective: The Isthmus of Uncertainty

“…Timing is based completely on the empirical choice of a reference electrogram and the setting of the mapping window. 2 Although this principle is apparent and most experienced electrophysiologists will either map and define the entire circuit of tachycardia or use entrainment mapping to identify appropriate sites for ablation, several corollaries to this principle are equally important but not as readily recognized. 3,4 P-Wave Morphology P-wave vector and morphology (or QRS morphology in the case of ventricular tachycardia) can be invaluable in estimating location of origin for a focal arrhythmia.…”