This week’s electrogram interpretation:
The following electrogram was recorded during an RF PVI ablation. The ablation catheter and HD Grid mapping catheter are located in the LSPV at the time of this recording.
The CS and His catheters are in their standard positions.
#1 – What are we trying to determine in this recording?
#2 – What signals/waveforms are despited as sites 1, 2, 3, and 4?
#3 – What is your interpretation?
Answer
Exit Block
#1:
During this maneuver, we are pacing the left superior pulmonary vein via the ablation catheter.
#2:
Signal at 1 is the A on the CS catheter, 2 is a far-field A on the HD grid recorded from within the PV, 3 is the local PV potential, and 4 is a far-field ventricular signal.
#3:
Exit block is observed in this example. Pacing within the pulmonary vein captured the local pulmonary vein tissue as noticed by the immediate signal observed on the HD Grid at arrow 3. Each pacing artifact captured the local PV tissue seen throughout the electrogram.
Now looking at the atrial activation on the CS catheter you will observe that the left atrial rate did not speed up to the pacing rate… the CS and pacing rate are completely unrelated.
This shows that the pacing from the PV captured the tissue but did not exit to the left atrium = exit block. Exit block aka isolating the pulmonary vein from the LA is the goal of this ablation. If this patient’s atrial fibrillation was triggered by firing within the pulmonary vein, it will now be corrected. If pulmonary vein firing remains, the signal will be unable to conduct to the left atrium and cause AF.
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If you like this, find hundreds of electrograms to interpret in our Understanding EP workbook – included in the Understanding EP book set.
For more information: EP Essentials – Understanding EP: A Comprehensive Approach
