Figure 3

The retrograde right atrial (RA) activation sequence of Halo catheter mapping by low lateral right atrium (LLRA) pacing (left two panels) and coronary sinus ostium (CSO) pacing (right two panels) in sinus rhythm in a patient with atrial flutter (atrial flutter +) and a patient without atrial flutter (atrial flutter −). Note that in the patient without atrial flutter, the collision site of the RA free wall and RA septal wavefronts is at Halo 5. However, in the patient with atrial flutter, the collision site shifts to Halo 7 during LLRA pacing and to Halo 3 during coronary sinus ostium pacing. S, pacing spike. The pacing cycle length was 250 ms, and the paper speed was 100 mm/s in all four panels.