Electrophysiologic characteristics and radiofrequency catheter ablation in patients with clockwise atrial flutter

RF Catheter Ablation of Clockwise Atrial Flutter, introduction: Although the mechanism and radiofrequency catheter ablation of counterclockwise (typical) atrial nutter have been studied extensively, information about the electrocardiographic and electrophysiologic characteristics and effects of radiofrequency ablation in patients with clockwise atrial Butter is limited, Methods and Results: Thirty consecutive patients with clinically documented paroxysmal clockwise atrial Butter were studied, Endocardial recordings and entrainment study using a ''halo'' catheter with 10 electrode pairs in the right atrium were performed, Radiofrequency energy was applied to the inferior vena cava-tricuspid annulus (IVC-TA) and/or coronary sinus ostium-tricuspid annulus (CSO-TA) isthmus to evaluate the effects of linear catheter ablation, Eighteen patients had both counterclockwise and clockwise atrial Butters, and 12 patients had only clockwise atrial Butter, Both forms of atrial nutter had similar nutter cycle lengths (232 +/- 30 vs 226 +/- 25 msec, P = 0.526) but reverse activation sequences, Right atrial pacing at a cycle length 20 msec shorter than the nutter cycle length from the CSO-TA isthmus, IVC-TA isthmus, and the area between the two isthmuses revealed concealed entrainment with stimulus-to-P wave intervals of 32 +/- 19, 95 +/- 14, and 50 +/- 17 msec (P = 0.022) in the counterclockwise form, and 110 +/- 12, 40 +/- 20, and 60 +/- 15 msec (P = 0.018) in the clockwise form. In clockwise atrial nutter 20 patients with biphasic P waves in the inferior leads had the presumed exit site of slow conduction area located at the low posterolateral right atrium; 10 patients with positive P waves in the inferior leads had the presumed exit site located at the mid-high posterolateral right atrium, Among the IS patients with both forms of atrial nutter, linear ablation lesions directed at the IVC-TA isthmus eliminated both forms of atrial nutter in 14 patients; in the remaining 4 patients, CSO-TA linear lesions eliminated the counterclockwise form and IVC-TA lesions eliminated the clockwise form. Among the 12 patients with the clockwise form only, CSO-TA linear lesions eliminated nutter in 2 and IVC-TA linear lesions eliminated nutter in 10 patients. Successful ablation was confirmed by creation of bidirectional conduction block in the IVC-TA and/or CSO-TA isthmus during pacing from the proximal coronary sinus and right posterolateral atrium sandwiching the linear lesions. During the follow-up period of 17 +/- 8 months, 2 patients had recurrence of clockwise atrial nutter, 1 patient had new onset of atypical atrial Butter, and 2 patients had new onset of atrial fibrillation. Conclusions: Counterclockwise and clockwise atrial flutters may have overlapping slow conduction areas with different exit sites. Radiofrequency catheter ablation using the linear method directed at the IVC-TA and CSO-TA isthmuses was feasible and effective in treating both forms of atrial nutter.