Figure 2 . Tracings show surface electrocardiograms in leads I, aVF, and V1, and electrograms of the tricuspid annulus (TA) and right atrial lateral wall (LW). A: During atrial tachycardia. Counterclockwise activation was observed in both the TA and LW. Activation was blocked in LW1, located on the posterior part of the cavotricuspid isthmus (CTI), and conduction delay was observed between TA4 and TA1, located on the anterior part of the CTI. B: During entrainment pacing from the lateral TA. The asterisks indicate the last captured beats, which returned with the pacing cycle length. The TA was captured directly by pacing (arrow a), whereas the LW was captured one cycle later than the TA (arrow b). Note that the LW was captured later than the proximal CS (TA1). C: During entrainment pacing from the proximal coronary sinus (TA1). The TA and LW were captured simultaneously by pacing (arrows c and d).