This electrogram was recorded during a cryoballoon PVI procedure. The PV catheter (Achieve) is in the LIPV.
What rhythm is observed in the following electrogram?
1. Atrial Tachycardia
2. Atrial Fibrillation
3. Sinus Rhythm
4. Junctional
Answer
Sinus Rhythm
The activation sequence is high to low and right to left such as in sinus rhythm. There is a P wave before each narrow QRS complex. The P wave is positive in Lead I (right to left) and positive in Lead aVF (high to low) Measurements are not displayed, but appear to be within the normal range.
Signal Recognition
What signals are circled on the pulmonary vein channels?
What is your interpretation?
1. Entrance Block
2. Exit Block
3. PV firing
4. Not Isolated
Answer
Pulmonary Vein Signal & Far-field Ventricular Signal
A sharp signal is typically seen with near field signals such as the first signal observed on the PV catheter in this example. A far-field signal is a smaller/blunted signal. The ventricle has a large mass or myocardial recruitment with depolarization; therefore, a small far-field V is often observed in the atria. The LIPV is closer to the ventricle hence the far-field ventricular signal.
During cryoballoon ablation, there is not an RF ablation catheter in the heart and typically only one transseptal access. Therefore, the LAA is not able to be paced to decipher if this is truly PV signal or far-field signal from the LA or LAA.
How may the physician test in order to make this determination?
Testing
What did the physician do to determine if this is truly a PV signal or far-field LA or LAA signal?
What is your interpretation?
Answer
Pace the PV
In this example, the physician is pacing the PV via the PV channel with the largest signal (PV 4,5).
The impulse captured the local tissue and conducted out the left atrium. This is observed by the CS rate matching the increased pacing rate.
The pulmonary vein is not isolated and further ablation is needed. During an RF ablation, the same thing may be performed. In addition, the physician may pace the RF ablation catheter from the LAA to help differentiate signals.
More Information:
For more information, please see: EP Essentials – Understanding EP: A Comprehensive Approach.
