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Figure 6-1: Explanation
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The PVC programmed into the cardiac cycle is relatively late coupled with minimal fusion and yet preexcites the next atrial cycle, so it is clearly AVRT. Earliest atrial activation is still near the CS os as identified on the ABL atrial electrogram, but now the atrial activation in the coronary sinus has shifted (long arrow) from distal to proximal, although the far-field PCS EGM is relatively earlier (short arrow). One may speculate that there is a now a left pathway but the atrial activation at the CS os (ABL catheter) is still very early. Ablation at this site terminated tachycardia and this was no longer inducible. The initial ablation at the CS os region likely resulted in interatrial block over the CS interatrial connection. Although AVRT was still occurring over a posteroseptal accessory pathway, there was a change in atrial activation of the LA resulting in a distal to proximal CS activation in spite of the origin of preexcitation near the CS os. This is infrequently seen with minimal ablation in the CS os region but is an interpretative issue that has consequences for successful ablation.
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Figure 6-2: Explanation
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The first observation is that there is some local activation after each pacing spike (asterisk) so that the spike is capturing the PV. The second is that the underlying rhythm is sinus (CL 890 milliseconds) and is dissociated from the paced activity inside the PV. The potentials in the pulmonary vein are "far field" coming from the left atrial appendage and this characteristically shows the biggest far-field potentials in the anterior part of the circumferential mapping catheter (i.e., 13–14, 11–12, 9–10, 7–8). Thus, "exit block" ...