Entrainment? Let’s break it down!

This is atrial flutter. Notice the regular atrial rate and that there are more atrial events than ventricular. We can also see that the CS is depolarizing from proximal to distal.

Is this typical AFL? How do you know? How can we test?

Entrainment! (As well as a nice 3D map shown later)

Entrainment is a pacing technique used to determine if the pacing electrodes are within the reentrant tachycardia circuit and in this AFL will help determine if the electrodes are in the critical isthmus. 

Entrainment for Atrial Flutter: 

1. Measure the TCL (tachycardia cycle length, A-A)
2. Pace, from the electrodes in question, approximately 20 ms faster than the TCL. Ensure that the pacing stimulus indeed captured the tissue and the the A-A sped to the PCL (pacing cycle length). Tachycardia MUST continue after pacing is stopped. 
3. Compare the pacing morphology to the tachycardia morphology.
4. Measure the PPI (Post Pacing Interval). This is measured from the last pacing stimulus to the return A on the pacing channel. 
5. Subtract the TCL from the PPI

Let’s practice!

 Pacing is occuring via the proximal coronary sinus. We paced faster than the TCL and the A-A during that time sped up to the pacing rate. When we stopped pacing, tachycardia continued. 

Next, we measured the PPI from the pacing stimulus to the return A on THAT channel. This equals 102 ms. If we divide that in half, it demonstrates that it takes 51 ms from the pacing electrodes to enter the AFL circuit, one trip around the circuit (340) and 51 ms back to the pacing electrodes. 

We want this number to be as close to zero as possible. The pacing morphology is similar to the AFL morphology, but with the long PPI – TCL, this is not in the critical isthmus of the tachycardia. 

In other words, this is not the area we want to ablate to successfully terminate the atrial flutter. 

Now we are pacing the distal coronary sinus which is on the left lateral aspect of the heart. We followed all the same rules of entrainment as explained before.

Here, notice that the pacing morphology on the CS is very different from the tachycardia morphology on the right. This is manifest entrainment.

Next, you can see with a PPI – TCL of 130 divided by 2 is 65 ms. So this is even further from the tachycardia circuit. 

In this final example, you can see we have concealed entrainment as the pacing morphology and the tachycardia morphology are identical.

The PPI – TCL is 8 ms.

With this information and concealed entrainment, we are in the critical isthmus for the tachycardia. A CTI ablation was then performed to treat the rhythm.

To close, here is the associated 3D map of the atrial flutter.

This map will be explained in future posts. However, notice the wave of depolarization from red/orange/yellow/green/blue/purple around the tricuspid valve shows the impulse traveling through the CTI, up the septum, over the roof, down the lateral wall, and back through the CTI again.  

This demonstrates typical counterclockwise atrial flutter.