Teaching Rounds in Cardiac Electrophysiology

Case Presentation No. 1 A 52-year-old man was referred for recurrent palpitations after 2 prior electrophysiology studies and ablations at an outside institution targeting right anteroseptal and left posterolateral accessory pathways (AP) for orthodromic reentrant tachycardia (ORT). Baseline ECG revealed sinus rhythm without preexcitation and an incomplete right bundle branch block. An ECG from his most recent tachycardia episode demonstrated a long RP tachycardia, with an incomplete right bundle branch block pattern at a rate of 135 beats per minute. Prior echocardiogram showed no evidence of structural heart disease. At electrophysiology study, the baseline atrial-His (AH) and His-ventricular (HV) intervals were both 58 ms. There was no preexcitation with incremental atrial pacing. There were spontaneous echo beats, which had a ventriculoatrial (VA) interval of 230 ms with concentric-appearing retrograde activation. Tachycardia with a cycle length (CL) of 460 ms was reproducibly initiated with programmed ventricular stimulation after a retrograde VA jump. Entrainment from the right ventricle (RV; mid-septum) showed a V-A-V response and a postpacing interval (PPI) of 583 ms without significant AH prolongation (Figure 1). Stim-A minus V-A time was 97 ms. Premature ventricular complexes (PVCs) from the septum during tachycardia advanced the atrium only if they were delivered ≥45 ms before the His deflection. Differential pacing was performed with entrainment from the RV apex yielding a PPI of 605 ms, whereas RV basal pacing resulted in a PPI of 601 ms. PPI from the proximalcoronary sinus (CS) was markedly prolonged (>50 ms over tachycardia CL) and was even longer from the mid CS (Figure 2). Mapping of the annular septum showed earliest retrograde activation at the mid right atrial (RA) septum. PPI with entrainment from here was 20 ms >tachycardia CL. What is the mechanism of the tachycardia, and what is the appropriate next step?