This week’s electrogram interpretation:
A 56-year-old female came into the EP lab with complaints of palpitations.
During initial catheter placement, the following electrogram was recorded. Only the His and CS catheters are in the heart at this time (CS in standard position / His catheter positioning is being obtained).
#1 – What was observed?
#2 – What should you think about preparing?
Answer
Ectopy revealing a left-sided accessory pathway
#1: Positioning the His catheter is inducing PACs. We can see this is coming from the His catheter because the earliest atrial activation is coming from the distal His (tip of the catheter). If it were originating from the SA node we would expect the earliest atrial activation on His proximal. An HRA catheter would also help differentiate this.
#2: There appears to be a left-lateral accessory pathway; therefore, transseptal equipment may be located to prepare for the next steps after the study is performed.
Let’s walk through each impulse… the first PAC from the His catheter travels down the AV node to the ventricle (notice the QRS and V signals).
The second impulse blocks in the AV node and does not conduct to the ventricle (no QRS or V).
The 3rd impulse travels down the AV node to the ventricle with delayed activation. Notice the longer A to QRS duration. This is a decremental property of the AV node in response to the faster rate (ectopy). Once this impulse reaches the ventricle it is able to travel back up to the atrium via an accessory pathway.
How do we know the location of the AP??
The earliest activation is on the distal CS which is located on the left lateral aspect of the heart. The signal is not bracketed so the catheter should be advanced for the EP study for a more complete evaluation.
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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
