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

Background-Activation mechanisms through gaps in ablation lines and resulting electrograms are poorly understood. Methods and Results-Eight patients tall men; age, 59 +/- 9 years) were studied 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 estimated, Maps created with 96 +/- 19 points revealed 0.8 +/- 0.3-cm gaps of recovered conduction in the ablation line. A broad wave front entered the lateral isthmus with a CV of 1.8 +/- 0.7 m/s, halted on the lesion line, and penetrated slowly through the gap with a CV of 0.3 +/- 0.1 m/s. Activation then 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 line with slow transverse activation (CV, 0.4 +/- 0.3 m/s) parallel to it. The ablation line was demarcated by an incomplete line of convergent double potentials with isoelectric intervals (from 123 +/- 34 to 62 +/- 16 ms); each potential corresponded to local activation upstream and downstream of the lesions, while the intervening delay was produced by slow conduction through the gap combined with the progressively longer curved pathway of downstream 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 antidromically activating its downstream flank, this detour producing wide double potentials on the line.