Are you sure you have entrance and exit block?

• how to verify isolation of pulmonary veins
• what exit and entrance block means
• what is the best sign of complete isolation

Isolation of the PV is confirmed by recording from within the isolated vein (most frequently with a spiral catheter). We want to have both entry and exit block of all veins.

• Entry block can be observed immediately after placing catheter in the veins if no local signal can be recorded on spiral catheter (be aware that frequently a far field signal from atrium will be present).
• For confirmation of exit block a pacing within all veins from all available electrodes is needed. No conduction from the pacing side distal to ablation line into left atrium can occur.
• One of the best spontaneous proof of the vain isolation is so called isolated/dissociated activity or potential of the pulmonary vain. It is an isolated signal occurring at spiral catheter but not conducting to atrium. It is frequently observed due to mechanical stimulus during catheter placement but can also occur as an automaticity beat.
• Another very important finding ensuring solid isolation is local capture within the veins when pacing from one of the catheter electrodes evoke potential within the vein that can be detected by other electrodes within being conducted to the atrium. This phenomenon is best to observe just behind ablation line where myocardial sleeves of the vain are still of substantial thickness.