Cavotricuspid isthmus conduction is dependent on underlying anatomic bundle architecture: observations using a...

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

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

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.

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%).

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.