Sometimes, the conversations in our FOAMfrat Slack channel are too good to be left behind closed doors. Follow along in a FOAMfrat slack channel conversation as myself (Tyler), and Josh Kimbrell (author of "False Electrical Capture in Prehospital Transcutaneous Pacing by Paramedics: A Case Series") collaborate to create a graphic illustrating true vs. false capture with transcutaneous pacing.
Tyler Christifulli 6:57am:
I’m throwing together a quick little group of trusty ECG peeps. Damian (our motion graphic designer) and I are working on building visual representations for the “False Capture” podcast I did with @Josh Kimbrell and Judah Kreinbrook. We are bottlenecking a little regarding accurately illustrating the difference between a “phantom complex” and actual ventricular depolarization. The only difference I can tell is a clear T wave follows that true ventricular depolarization. So here are my questions
In this case, we have TRUE capture because we see a clear T-wave
In this case, we also have TRUE capture
Tyler Christifulli 6:58 am:
The ventricular depolarization or downstroke following the pacer spike is wider in the second picture than in the first. In Tom’s OG blog, he shows how this complex gets bigger with more electricity.
So, that can’t be the heart depolarizing because it wouldn’t get bigger every time you increase the electricity, right?...... Lol, but if there was a T-wave after it, it would be.
Josh Kimbrell: 7:30 am
Yes, and this arcing phantom complex is a morphology that is often clearly not a QRS (it looks like an immediate return to the isoelectric line rather than more defining features of the QRS). As Tom noted, this is difficult because it gets bigger with larger currents.
Josh Kimbrell: 7:31 am
Here is another example
Josh Kimbrell: 7:32
This is a relatively obviously false electrical capture from the 12L, with some leads showing a very small phantom complex, but as you can see in aVF, it can be tricky.
Josh Kimbrell: 7:33
Here, they increase the current until they get a large QRS with a T wave
Josh Kimbrell: 7:52 am
I'm not sure how to articulate the difference more clearly, but let me try. The phantom complex is an electrical artifact, so the waveform is narrow and returns to the isoelectric baseline quickly (it may, as seen in some of these examples, overshoot slightly and need to arc back down a little). The QRS is a larger morphology with more on its agenda, so to speak than returning to baseline. It should be large, broad, and discordant.
Tyler Christifulli: 8:58 am Is the phantom complex hidden by the ventricular depolarization in true capture? I think that is the main point I am trying to articulate with this illustration.
Josh Kimbrell: 9:01 am
It is not always hidden; it is in the first one you sent.
Tyler Christifulli: 9:02 am
Where is the phantom complex here?
Josh Kimbrell: 9:02 am
There is none there. It's not always gonna be there.
Tyler Christifulli: 9:03 am
Where is it here?
Josh Kimbrell: 9:04 am
Here, I would say the first upstroke.
Tyler Christifulli: 9:04 am
ok, that helps! I swear I am not trying to harass you about this just want to make sure we illustrate it as accurately as possible, and with ECG, it can be hard to account for nuance/artifact, etc.
Tyler Christifulli: 9:10 am
@Josh Kimbrell, does this look correct?
Tyler Christifulli: lol sorry for the random airport noises in the back
Josh Kimbrell: 9:14 am
Yes, that's exactly right. Tom Bouthillet argued that the final bump you didn't have illustrated is actually an artifact from a muscular contraction, but totally not necessary for this educational illustration.
Tyler Christifulli: 9:16 am
I just set a record for the fastest meme
Josh Kimbrell: 9:16 am
Lmao! I love that; incredible
Tyler Christifulli: 9:23 am
reminded me of this because when it peaks through it is only half of the complex lol
Tyler Christifulli: 9:23 am
Oh, snap! I have an idea!
Tyler Christifulli: 9:32 am
Something like this for an infographic
Tyler Christifulli: 10:02 am
I also talked to Tom, and I will make a few changes to the false capture one. Tom said the false one has more of a slope on the way up, overshoots a tad, and then comes back down.
Tyler Christifulli: 10:39 am
and now for the final graphic!
References:
Kimbrell, J., Kreinbrook, J., Poke, D., Kalosza, B., Geldner, J., Shekhar, A. C., Miele, A., Bouthillet, T., & Vega, J. (2024). False Electrical Capture in Prehospital Transcutaneous Pacing by Paramedics: A Case Series. Prehospital emergency care, 1–9. Advance online publication. https://doi.org/10.1080/10903127.2024.2321287
