This week’s electrogram interpretation:
What is observed in the following electrogram?
The ablation catheter is located in the CTI.
Answer
Concealed Entrainment of Right Atrial Flutter
The rhythm on the right half of the electrogram is atrial flutter with activation from proximal to distal coronary sinus. However, the CS activation sequence alone does not rule out left atrial flutter. If the flutter circuit is traveling around the mitral valve in the counterclockwise direction it will demonstrate this sequence.
So, how do you determine if this is a right or left atrial flutter?
…Entrainment.
In this example, entrainment was performed via ABL D which is located in the cavotricuspid isthmus. To entrain, pace 20 ms faster than the tachycardia cycle length. After pacing, the tachycardia must continue and the post pacing interval is measured on the pacing channel from the pacing artifact to the return A. The tachycardia cycle length is then subtracted from the PPI to determine the distance the pacing electrodes are from the tachycardia circuit. If the resulting number is less than 30 ms the pacing electrodes are within the circuit.
In this example, 300 (PPI) – 300 (TCL) = 0 ms.
With the PPI – TCL of 0 ms, the pacing electrodes are within the tachycardia circuit. This is a right atrial flutter.
Also of note is the concealed appearance. The pacing morphology is the same as the tachycardia morphology. Since the PPI – TCL is less than 30 ms with concealed entrainment, the pacing electrodes are within the critical isthmus.
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For more information: EP Essentials – Understanding EP: A Comprehensive Approach – section on atrial flutter entrainment.
