• atrial flutter;
  • cavotricuspid isthmus;
  • ablation;
  • voltage guide

Objectives: We hypothesized an ablation strategy directly targeting muscle bundles might demonstrate functionally distinct “routes” of conduction, potentially shortening ablation times.

Background: Pathological study demonstrated that the cavotricuspid isthmus is composed of distinct anatomically defined bundles, many with intervening gaps of connective tissue.

Methods: A line was mapped in the “6 o'clock” region and bipolar electrogram amplitude measured during pullback. Zones of peak voltage were ablated first regardless of position. RF was delivered using either a 5-mm externally irrigated catheter, or an 8-mm nonirrigated catheter. The zone of largest remaining voltage was then sequentially targeted until conduction.

Results: Eighteen patients were recruited and followed for 7.9 ± 1.9 months block occurred (mean age 64 ± 11.6 years, male:female ratio 14:4). Bi-directional block was achieved in all patients with recurrence of atrial flutter in 1 patient. Mean total RF times was 4.7 ± 2.8 minutes with a mean of 6.1 ± 3.3 applications, procedure time was 127.3 ± 37.7 minutes, and fluoroscopy time was 25.5 ± 12.0 minutes. Two patterns of block were observed in the study group. Pattern A described no change in conduction times until block, observed in 6 (33%); pattern B described a stepwise block with discrete “jumps,” observed in 12 (67%).

Conclusions: An ablation strategy targeting high-voltage isthmus electrograms obviates the need for a complete anatomic line. This finding together with discrete “jumps” during ablation is consistent with the concept of conduction over discrete bundles rather than a diffuse sheet of muscle.