What are we looking at?
How would you interpret the following electrogram?
Is it completely normal, just here to get you thinking?
Is there pacing? If so, from which site? Did it capture & conduct?
Anything other observations?
Answer:
In this electrogram we can observe ventricular pacing and capture with each pacing impulse.
Notice the pacing spike on the surface ECG immediately followed by the wide QRS complex.
We are performing decremental pacing as observed with the decreasing pacing cycle length (pacing faster… 380, 370, 360 …).
The first three impulses display fairly concentric activation. It doesnt look quite “normal” as CS 1,2 is slightly earlier than CS 3,4; however, the earliest atrial activation still appears to be on the His cathter (not seen well) or the proximal CS. So it appears that the impulse is traveling from the ventricle to the atrium through the AV node / septal region.
Next, look at the last three impulses. Do you see the difference? What changed?
Notice the shift in atrial activation in which now the earliest A is on CS 1,2 or distal CS. This is eccentric activation, or abnormal activation, via an accessory pathway on the left side of the heart. It was not clear on the first three impulses as the impulse was traveling up to the atrium through the AV node as well as the pathway. This is observed in the following example.
At 360 ms (impulse #4), the AV node blocked but was still able to travel up to the atrium through the accessory pathway. This is what causes the shift in activation observed here, treatment would be ablation of the pathway.
More information on accessory pathways and electrophysiology from the basics through advanced may be found in Understanding EP: A Comprehensive Guide by Dr. Paul Haas.
