A 36-year-old female presents to the EP lab with complaints of palpitations. They come on 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. Many complete case studies of all the common tachycardias may be found in the Understanding EP online course.
Baseline Testing
What is observed in the following electrogram?
1. AV Block
2. VA Block
3. AVN ERP
4. 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.
Baseline Testing
What is observed in the following electrogram?
1. AV Block
2. Crossover
3. Dual AV nodal physiology
4. Activation switch to accessory pathway
Answer:
Dual AV Nodal Physiology
What is the most likely rhythm observed in the following electrogram?
1. VT
2. AVRT
3. AVNRT
4. Atrial Tachycardia
Answer:
AVNRT
This rhythm appears to be AVNRT. Notice how the As and Vs appear to be stacked or 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.
Interpret the following ventricular overdrive pacing attempt.
1. VAV – AVNRT vs. AVRT
2. VAV – Atrial Tachycardia
3. VAAV – AVNRT vs. AVRT
4. VAAV – Atrial Tachycardia
5. Not entrained
Answer:
VAV – AVNRT vs. AVRT
Ventricular overdrive pacing met all the rules of entrainment. We captured the ventricles, 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.
Where is the ablation target for this rhythm?
1. Site of AV fusion
2. Fast Pathway
3. Slow Pathway
4. Crista Terminalis
5. CTI
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.
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If you like this, find hundreds of electrograms to interpret in our Understanding EP workbook – included in the Understanding EP book set.
For more information: EP Essentials – Understanding EP: A Comprehensive Approach
