High-density mapping of activation through an incomplete isthmus ablation line

Background-Activation mechanisms through gaps in ablation lines and resulti ng electrograms are poorly understood. Methods and Results-Eight patients tall men; age, 59 +/- 9 years) were stud ied during a recurrence of typical atrial flutter (cycle length, 233 +/- 19 ms) after a previous catheter ablation in the cavotricuspid isthmus. High- density 3-dimensional mapping of the isthmus was performed with the Cordis- Biosense EP Navigation system, and local conduction velocity (CV) was estim ated, Maps created with 96 +/- 19 points revealed 0.8 +/- 0.3-cm gaps of re covered conduction in the ablation line. A broad wave front entered the lat eral isthmus with a CV of 1.8 +/- 0.7 m/s, halted on the lesion line, and p enetrated slowly through the gap with a CV of 0.3 +/- 0.1 m/s. Activation t hen curved and returned antidromically to activate the downstream flank of the line with a CV of 1.1 +/- 0.7 m/s. This front fused downstream of the l ine with slow transverse activation (CV, 0.4 +/- 0.3 m/s) parallel to it. T he ablation line was demarcated by an incomplete line of convergent double potentials with isoelectric intervals (from 123 +/- 34 to 62 +/- 16 ms); ea ch potential corresponded to local activation upstream and downstream of th e lesions, while the intervening delay was produced by slow conduction thro ugh the gap combined with the progressively longer curved pathway of downst ream antidromic activation as a function of distance from the gap. Conclusions-High-density isthmus mapping during recurrent flutter indicates slow conduction through gaps of recovered conduction of varying dimensions in the ablation line followed by a curved front of activation antidromical ly activating its downstream flank, this detour producing wide double poten tials on the line.