Part 1 - Baseline Testing
A 36-year-old female presents to the EP lab with complaints of palpitations which occur spontaneously regardless of activity. She says that it may last for several minutes and then spontaneously terminates. She has discovered that she can often cough and self-terminate the rhythm. It is occurring more frequently, so she decided to get it corrected.
An abbreviated case study is to follow.
The following electrogram was recorded during baseline testing.
What is observed?
- AV Block
- VA Block
- AVN ERP
- Retrograde AVN ERP
Answer: VA Block
In this example, we are pacing the ventricle (decremental pacing) and watching the activation up the AV node to the atrium. Notice the early atrial event is seen on the His channel showing concentric activation.
The 4th impulse captures the ventricle but no longer conducts to the atrium – VA block.
What is observed in the following electrogram?
- AV Block
- Dual AV nodal physiology
- Activation switch to accessory pathway
Answer: Dual AV Nodal Physiology
This example is of decremental atrial pacing via the HRA catheter. The PR interval in a normal heart will decrement or slowly stretch out; however, in this example, the PR goes from 186 to 253 ms. It “jumped” out 67 ms. This is evidence of a slow pathway in which the fast pathway reached ERP and the impulse “jumped” to the slow.
Part 2 - Tachycardia
What is the most likely rhythm observed in the following electrogram?
- Atrial Tachycardia
This rhythm appears to be AVNRT. Notice how the A and V signals appear to be stacked (a VA interval <60 ms.) Retrograde activation of the atria is concentric although a good His signal was not acquired.
Though this appears to be AVNRT, differential pacing maneuvers should be performed.
Part 3: Tachycardia Testing & Ablation Site
Interpret the following ventricular overdrive pacing attempt.
- VAV – AVNRT vs. AVRT
- VAV – Atrial Tachycardia
- VAAV – AVNRT vs. AVRT
- VAAV – Atrial Tachycardia
- Not entrained
Answer: VAV- AVNRT vs. AVRT
Ventricular overdrive pacing met all the rules of entrainment. We captured the ventricle, sped up the atrial rate, and tachycardia continued when pacing ceased. This pacing maneuver helps rule out atrial tachycardia which has a VAAV response. To further identify the rhythm, the tachycardia cycle length (TCL) is subtracted from the post pacing interval (PPI). A result less than 115 ms correlates with AVRT and greater than 115 with AVNRT.
PPI – TCL = 654 – 430 = 224 ms.
This result is greater than 115 leading to a diagnosis of AVNRT.
To understanding the meaning behind this measurement instead of just memorizing the numbers, please view the Understanding EP online program and/or textbook.
Part 4: Ablation Strategy
Where is the ablation target for this rhythm?
Site of AV fusion
Answer: Slow Pathway
The target location is at the slow pathway. The fast pathway is needed for normal conduction and should not be ablated. During RF ablation of the slow pathway, slow junctional beats are observed.
In this 3D image, an RAO and LAO view is displayed. The fast pathway is located anterior and septal and marked here with the yellow His catheter and yellow tags. The slow pathway is located more posteriorly. The colored lesions displayed are where RF energy is applied. The various colors are related to the impedance drop seen with the lesion.