CASE PRESENTATION
A 37-year-old man was referred to our institution for ablation of a
cavotricuspid isthmus (CTI)-dependent atrial tachycardia (AT). The AT
was terminated by linear ablation to the CTI. However, the same AT
recurred, and a second procedure was performed. A surface
electrocardiogram showed flutter waves with a negative deflection in the
inferior leads (Fig. 1A). To assess the detailed activation sequence of
the AT, two 20-pole deflectable electrode catheters were placed in a
parallel position on the tricuspid annulus (TA) and right atrial lateral
wall (LW) (Fig. 1B–D). During AT (cycle length: 280 ms),
counterclockwise activation was observed in both the catheters, and a
gap with conduction delay was observed on the anterior part of the CTI
block line (Fig. 2A). During entrainment pacing from the lateral TA, the
LW was captured one cycle later than the TA (Fig. 2B). In contrast,
during entrainment pacing from the proximal coronary sinus (CS), the TA
and LW were captured simultaneously (Fig. 2C). AT was terminated during
radiofrequency application to the gap on the CTI block line. After the
termination of AT, the completion of the CTI block line was confirmed.
AT did not recur after the procedure. What is the mechanism of the
delayed capture of the LW during entrainment pacing from the lateral TA?