fWhat is happening in this electrogram during baseline testing?
Resist the urge to jump ahead; instead, start with the basics.
- Where are each of the catheters located?
- Are we pacing?
- What type of pacing and from where?
- Did we capture?
- Did it conduct?
- What was the activation pattern?
Answer:
The catheter positions match the color of the channel displayed.
Green – Decapolar (10 electrode) catheter in the coronary sinus (CS), which originates in the posterior septal area of the right atrium (RA). The CS then travels epicardially in between the left atrium (LA) and left ventricle (LV), therefore displaying an A (atrium) and V (ventricular) signal.
Yellow – Quad at the AV Node / Bundle of His location, which is positioned partially in the atrium and partially in the ventricle, just passed the tricuspid valve (TV). There should be three signals observed (A, H, V) with correct placement; however, the catheter was advanced further into the ventricle to be able to pace the RV.
RV pacing is occurring via the His catheter, and capture is observed by the immediate ventricular depolarization (image below). This is best seen on the surface ECG with the wide QRS complex. Decrmental pacing is being performed in which the pacing rate is slowly increased (faster and faster). Notice pacing begins at 550 ms and then is paced faster at 540, 530 ms.
Notice the circled beat. This does not correspond with a pacing artifact, and the QRS complex came in earlier than expected. This is a PVC or premature ventricular contraction. The PVC did not conduct to the atrium, as you can tell by the lack of a corresponding A signal on the CS.
What is observed at the circled event?
Answer:
The circled pacing artifact is too soon after the PVC. The ventricular tissue is still refractory from the PVC and is unable to depolarize at this time. The cells have not repolarized to a sufficient level to be able to depolarize again.
If you looked at the original electrogram too quickly, you may have mistaken this as a VA block.
