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Figure 3 Three-dimensional activation patterns in a patient with paroxysmal atrial fibrillation. Isochrones are drawn every 5 ms. Splines A and B are located in the posterior wall, splines B, C and D in the septal wall, spline E across the tricuspid annulus and splines G and H are located in the lateral wall of the right atrium (RA). Electrode pairs 1/2 are located in the upper RA, whereas electrode pairs 7/8 are located in the lower RA. Grey ellipse shows position of the tricuspid valve. Red represents the head of activation front. At time 0, an early breakthrough is observed in the high septal region. After 74 ms, almost the entire RA was activated from that spot. At the level of electrode pair B 6/7 (low posterior region), the main wave front is divided into two wave fronts heading toward the low posterior (electrode B 7/8) and posteroseptal (electrode C 5/6) regions. After 107 ms, the lateral wave front crossed the isthmus region and emerged at the low septal region, whereas the posteroseptal wave front activated most of the posteroseptal area. At 174 ms, two wave fronts are just re-entering the posterior and the lateral regions again.