What is happening in this electrogram?
Where to begin….?
- 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 – Quadripolar (4 electrode) catheter in the HRA (high right atrium) near the SA node. This channel will display atrial activation (A).
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 3 signals observed (A, H, V).
Blue – 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 and A (atrium) and V (ventricular) signal.
Red – Quad at the RVa (right ventricular apex). This catheter should only display ventricular activation.
Pacing is occurring via the RV 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 300 ms and then is paced faster at 290 ms.
On the first portion of the electrogram, each ventricular paced beat conducts to the atrium. This can be watched in various ways but is often easiest for newer staff members to watch the surface QRS to the HRA channel.
The activation pattern is concentric or normal, traveling to the atrium through the bundle of His / AV node. This is observed by the earliest atrial activation seen on the His channels.
Of interesting note, the VA conduction time is very delayed. We don’t often seen this much VA decrement (VA or AV stretching) on a patient unless they have a slow pathway as well.
On the last portion of the electrogram (below), you observe one impulse that was unable to conduct to the atrium. It did capture the local ventricular activation as seen by the wide QRS complex but there is no corresponding A on the HRA or CS channels. This is VA block. The next impulse then conducts as the AV node had more time to recover. If pacing were to continue, block would continue to be observed.
