Patient Example (Case 4)
Figure 1 shows ECGs during sinus (A) and reentrant arrhythmia (B) of a patient example (Case 4) who underwent 3 slow pathway ablations prior to the current study. This patient had been in this incessant arrhythmia shown in panel B after the 3rd ablation. The surface ECG showed a very slow junctional type arrhythmia (HR 75/min), and the patient was significantly symptomatic when in this arrhythmia. The patient was treated as having a junctional arrhythmia, and beta-blocker therapy was prescribed, which did not improve her symptom. Due to the inefficacy of this treatment, the patient was referred for further possible ablation. Intracardiac studies showed simultaneous VA activation with septal VA timing of 59ms. VOD showed V-A-V response with PPI-TCL 177ms (Figure 2). AES delivered during the slow pathway refractory period (on time with retrograde fast pathway depolarization) terminated the tachycardia, which proved that slow pathway conduction was part of the tachycardia mechanism (Figure 3) . AOD delivered from CS 1-2 successfully entrained the tachycardia. The septal PPI-TCL confirmed a reentrant mechanism (Figure 4) . After the successful slow pathway ablation, this tachycardia could never be inducible, and the patient became asymptomatic.