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Figure 5 Pacing at a remote bystander site where an isolated potential (IP) is present is shown. From the top of the figure are 10-ms time lines, surface electrocardiogram leads I to V6 and bipolar recordings from the distal (A-BI-D) and proximal (A-BI-P) electrode pair of the left ventricular mapping catheter and the right ventricular apex (RVA). Sustained monomorphic ventricular tachycardia with a cycle length (CL) of 320 ms is present. The last three stimuli (S1) of a stimulus train at the mapping site are shown. Pacing at a CL of 310 ms entrains tachycardia with QRS fusion. In the left ventricular recording the postpacing interval (PPI) is 380 ms and therefore exceeds the tachycardia CL by 60 ms, consistent with a bystander site. An IP is present marked with arrowheads and the main component of the electrogram is marked with arrows. The amplitude of the IP is 0.7 mV and duration is 40 ms. All measurements are in milliseconds.
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