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Figure 3 Display of lead II, bipolar electrograms (A) at 10 endocardial locations (B) and body surface potential maps (C) acquired during CW typical atrial flutter in patient 5. The ECG waveform below each map was sampled at the C1 lead site (right upper anterior torso) (see Fig. 1 and 2 for further explanation). The potential maps obtained during the first 76 ms demonstrate stable inferiorly oriented forces while craniocaudal excitation of the medial anterior free wall (site 1), septum and CSO (site 2) is occurring. For the next 80 ms a second stable map pattern emerges and shows leftward directed forces as a result of concurrent activation of the isthmus (site 3 is located at the exit) and CS in opposite directions. Finally, a third pattern may be observed featuring stable right superior forces during the remaining 64 ms of the Fl wave when the entire free wall is activated in a caudocranial direction (sites 4 to 9). It may be noted that septal activation and subsequent combined isthmus and CS activation occur during the first and second part of the positive M-shaped component in lead II, respectively. The anatomic diagram of the right atrium is reproduced with permission of Gower Medical Publishing. CSO = coronary sinus os; CT = crista terminalis; FO = fossa ovalis; IVC = inferior vena cava; SVC = superior vena cava.
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