This week’s electrogram interpretation:
This patient is in the lab for an SVT study. A four-catheter EP study was performed with the catheters in the standard locations.
The following series of electrograms were recorded during baseline extra-stimulus testing.
#1 – What was observed?
#2 – Which SVT is essentially ruled out with this finding?
Answer
VA decrement – Ruling out AVRT
Extra-stimulus testing is performed from the RV catheter as seen by local RV capture as well as a wide surface QRS complex. Here the drivetrain is not shown, just the extra-stimulus for the ability to easily compare.
After each drive, the PVC was continuously brought in sooner by 10 msec. For ease of display, not each run is shown. Notice how the interval from the V to the A gets progressively later. This is referred to as decremental conduction which is associated with AV nodal conduction.
Accessory pathways do NOT conduct (rare exceptions may be seen).
Therefore, AVRT is essentially ruled out with this baseline pacing maneuver.
EP is all out ruling things out.
Notice the last run with the extra-stimulus at 240 ms the VERP was reached. The impulse came in so soon that the ventricular tissue itself was unable to depolarize.
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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
