response of pulmonary vein potentials to burst pacing background pulmonary vein potentials recorded at the ostia of pulmonary veins pv are a useful guide for segmental isolation of the pv in patients with atrial fibrillation af even during coronary sinus pacing at 600 ms atrial a and pv potentials can overlap in 5060 of patients making the accurate identification of pv potentials very difficultmethods nineteen patients mf 154 with paroxysmal af underwent segmental isolation of one or more pv coronary sinus cs pacing was performed at cycle lengths of 600550500450400350300 ms and bipolar electrograms were recorded from the 10 or 20 pole lasso catheter placed at the atrialpv junction in 27 pulmonary veins stimulus s to a spvp and apvp intervals were measured during cs pacing at the different cycle lengths at sweep speed of 200 mmsecresults during cs pacing at 600 ms the a and pv potentials were significantly overlapped apvp or 25 ms in 9 of the 15 veins where a and pv potentials overlapped and 21 of all 27 78 veins in two patients pacing at 300 ms was associated with 21 conduction block from atrial to pv fascicleconclusions coronary sinus pacing at cycle length of 300 ms demonstrated better separation of a and pv potentials compared to pacing at 600 ms this strategy is easier and less time consuming compared to extrastimuli testing it also confirms that the electrophysiological properties of pv fascicles are different from that of the adjacent atrial musculature