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Background-The extent of ostial ablation necessary to electrically disconnect the pulmonary vein (PV) myocardial extensions that initiate atrial fibrillation from the left atrium has not been determined. Methods and Results-Seventy patients underwent PV mapping with a circumferential 10-electrode catheter during sinus rhythm or left atrial pacing. After assessment of perimetric distribution and activation sequence of PV potentials, ostial ablation was performed at segments showing earliest activation, with the end point of PV disconnection. A total of 162 PVs (excluding right inferior PVs) were ablated. PV potentials were present at 60% to 88% of their perimeter, but PV muscle activation was always sequential from a segment with earliest activation (breakthrough). Radiofrequency (RF) application at this breakthrough eliminated all PV potentials in 34 PVs, whereas a secondary breakthrough required RF applications at separate segments in 77; in others, Ͼ2 segments were ablated. A median of 5, 6, and 4 bipoles from the circular catheter were targeted in the right superior, left superior, and inferior PVs, respectively, to achieve PV disconnection. Early recurrence of arrhythmia was observed in 31 patients as a result of new venous or atrial foci or recovery of previously targeted PVs, most related to a single recovered breakthrough that was reablated with local RF application. Conclusions-Although PV muscle covers a large extent of the PV perimeter, there are specific breakthroughs from the left atrium that allow ostial PV disconnection by use of partial perimetric ablation.

AF 5 atrial fibrillation; LOE 5 Level of Evidence; HCM 5 hypertrophic cardiomyopathy. **A decision to perform AF ablation in an asymptomatic patient requires additional discussion with the patient because the potential benefits of the procedure for the patient without symptoms are uncertain.

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