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Figure 4 Random re-entry in a patient with chronic atrial fibrillation. A time window of 100 ms is shown. Spline locations were: splines A and B in the posterior wall, splines C and D in the septal wall, spline E across the tricuspid annulus and splines F, G and H in the lateral wall. At time 0, two wave fronts in the right atrium were observed. After 20 ms, the posterior wave front goes up the posterior wall, whereas the lateral wave front is divided into two wave fronts going up and down the lateral wall. After 40 ms the posterior activation front reaches the high right atrium. The lateral wave fronts move toward the higher and lower areas. A new wave front moves toward the tricuspid annulus (electrode pair G 5/6). At 60 ms, posterior and lateral wave fronts enter the high septal region. At 80 ms, a collision of wave fronts is observed in the high septal region, and a new division is observed in the low lateral region. At 100 ms, one of the lateral wave fronts crossed the isthmus region and entered the septal region, whereas the other wave front re-enters the midlateral wall. Meanwhile, the septal wave front is divided into two wave fronts, heading for collision with the wave front coming through the isthmus and the other one (electrode pair A 3/4) moving toward the midposterior section.