The Dangling Electrogram: Discerning Spatial from Electrophysiological Distance

A 63-year-old male who had previously undergone an orthotopic cardiac transplant with a cavocaval anastamosis presented with persistent atrial tachycardia. Catheters were placed using a femoral approach for a conventional EP study. There was difficulty cannulating the coronary sinus and therefore, the decapolar catheter was placed along the lateral right atrium (RA). A 4 mm tip ablation catheter was used for mapping in the RA. During mapping, a site of apparent early endocardial activation was identified along the mid lateral RA. Figure 1 shows atrial pacing from the mapping catheter (labeled “MAP” in the figure) at cycle length (CL) 300 ms dur-