Catheter-mediated linear block in the atria.

To the Editor: In a recent issue of Circulation, Pappone et al1 report their experience with catheter ablation for atrial fibrillation using long atrial linear lesions. Because they emphasized their difficulty in assessing the completeness of lines, we would like to clear up certain misconceptions concerning this issue. First, the idea that the spatial continuity of marked lesional points indicates line completeness is erroneous because no information about the electrophysiological consequences is incorporated. Furthermore, the completeness of linear lesions can be verified simply by recording widely separated double potentials all along the line (during orthogonal activation). The requirement for $60 ms of conduction delay between 2 points separated by ,1 cm has no rationale because the interval obviously depends on the length of the line as well as on the site of pacing, average velocity, and relationship to other regions of anatomical block. We reported endocardial (all along the line) and epicardial (through the coronary sinus) double potentials of 104635 ms with complete lines from the right superior pulmonary vein ostium down to the mitral annulus.2,3 For such a line, a coronary sinus catheter recording double potentials provides the simplest evidence of its completeness. The addition of another complete line joining both superior pulmonary veins typically increases the double potential interval to 160 to 200 ms.2,3 The ablation schema chosen by Pappone et al1 in the left atrium is, in fact, ideal for demonstrating the completeness of linear lesions because it creates regions of complete electrical isolation (which should produce either dissociation or no recordable electrical activity). Any evidence of 1:1 activation in these encircled regions (as indicated by the late activation in Figure 2) is proof of $1 electrically incomplete boundary.