What are we doing??
Tachycardia is displayed on the right half of the electrogram, and the differential pacing attempt is on the left.
Where do we even begin?
- Where are we pacing?
- What type of pacing?
- Did we capture?
- What maneuver is being performed?
- Are we able to interpret the maneuver?
Answer:
We are pacing the right ventricle as noted by the pacing spike immediately followed by a wide QRS. Ventricular capture is also observed on the RV electrogram (blue).
Pacing is occurring 20 ms faster than the tachycardia cycle length (TCL). This is observed with the cycle length annotation on the right (circled) at 260 ms and on the left (circled) at 280 ms.
Burst pacing is performed or pacing at a fixed rate.
The maneuver that is being performed is ventricular overdrive pacing. This may also be referred to as a type of entrainment.
Lets work on interpretation.
Did we successfully performed ventricular overdrive pacing?
How would you interpret this result?
What does it mean?
Answer:
As noted previously, we did successfully capture the ventricular myocardium while pacing 20 ms faster than the TCL. The corresponding atrial activity also advanced to 260 ms and the tachycardia continued after pacing was completed; therefore, the results may be interpreted.
- Notice the post entrainment response of VAV. This rules out atrial tachycardia which displays a VAAV response.
- The post pacing interval measured 379 ms, we then subtract the TCL.
- 379 (PPI) – 280 (TCL) = 99 ms
- This result is in favor of AVRT (over AVNRT)
- PPI-TCL = <115 = AVRT
- PPI-TCL = >115 = AVNRT
This first example shows an accessory pathway on the right side just out of ease of illustration.
Notice that from the pacing site, it takes minimal time to enter into the circuit (<115 ms). This is because the ventricle is part of the circuit.
In this 2nd example of AVNRT, the dashed line represents the time it takes to travel to the circuit which is confined to the AV node. This time to travel through the ventricular myocardium takes longer than the previous example, or >115 ms.
For more detailed information and examples, please refer to the Understanding EP: A Comprehensive Guide book set.