How do we determine success?
A patient undergoing PVI (pulmonary vein isolation) for paroxysmal atrial fibrillation is in the lab. After completion of the WACA (wide area circumferential ablation), there was remaining signal in the left superior pulmonary vein. The physician is unsure if this is local pulmonary vein signal or if the vein is truly isolated and the signal is far field from the LAA.
What would you recommend?
Answer:
Testing for exit block may be beneficial to differentiate signal.
How do you interpret this electrogram?
Testing for exit block may be beneficial to differentiate signal. This was performed in the following 
electrogram. The catheters displayed are a decapolar CS and an Octaray (8 spline catheter) that is currently in the LSPV.
Answer:
Pacing is occurring via B1,2 as noticed by the distortion on the channel. Immediately after the pacing artifact, local capture of the pulmonary vein is observed. However, this is not able to conduct out of the PV to the atrium. Notice that the atrial signal on the CS was not brought in early with pacing. The pulmonary vein pacing did not exit the vein, this is exit block. This helps to show that the signal the physician observed earlier (not displayed) was far field left atrial/LAA signal and LSPV isolation is complete.
In the following illustration, the octaray is in the LSPV with pacing, but the wave of depolarization is unable to travel past the line of block created with ablation.
For more information, please refer to the Understanding EP: A Comprehensive Guide.
