TCP False capture - True Capture?

[rhan101277]

I had a call for a 83 y/o female with SOB. We get there she is not responsive but had adequate RR with diffuse rales and a hx of CHF and heart problems, previous strokes and MI's.

I put her on oxygen because I am getting sats of 65%. I then put her on the monitor and have 3rd degree HB at a rate of 20 and I can't hear a BP.

I pace at 70bpm/50ma and I feel I have got capture even though the QRS looks like "phantom QRS waves". Her b/p comes up and sats come up so treating the patient not the monitor. Still it appears that the underlying rhythm is marching through the paced QRS at where the absolute refractory period should be and this is impossible. My vitals signs increased and I checked the underlying rhythm several times during pacing and it was the same. Any thoughts? Normal paced rhythm has broader QRS and wide T waves, but I treated patient.

Thoughts?

 

[Maine iac]

Did her pulse match what the EKG was showing? It looks like there are a few ectopic beats in there, but appears to capture.

I was always told that once I get capture increase the amps by 1 (push the increase button once more).

 

[rhan101277]

Yeah it did match, but the QRS and t wave looks much like what they call "phantom QRS" in this article.

http://ems12lead.com/2008/11/transcutaneous-pacing-tcp-the-problem-of-false-capture/

There are many factors that lead me to believe I had full capture, mechanical and electrical. The first QRS wave in my paced strip looks to be in the absolute refractory period to me and if it is it can't be electrical capture.

All the patient vitals went up though including sats, this article just throws a wrench in it though and makes me wonder. A good paced rhythm looks like this.

http://3.bp.blogspot.com/_2MjIeQJj8UM/SR8Di9Zy34I/AAAAAAAAAXU/Gdvvc5T-ZR4/s1600-h/TCP+case+14.jpg

Last one on the bottom

Also this..

http://www.physio-control.com/uploadedFiles/learning/clinical-topics/Pacing_Artifact_3207454-000.pdf

 

[Maine iac]

If I was to only compare your second EKG to the one in the EMS12lead link I'd say it was not a capture. But, you were there and I wasn't, so if you say everything improved then I guess that answers your question.

Did you try going higher than 50mA? Or did you stop there because things improved.

I've only paced plastic before so I am just going off that article and what I've read/been taught.

 

[rhan101277]

If I was to only compare your second EKG to the one in the EMS12lead link I'd say it was not a capture. But, you were there and I wasn't, so if you say everything improved then I guess that answers your question.

Did you try going higher than 50mA? Or did you stop there because things improved.

I've only paced plastic before so I am just going off that article and what I've read/been taught.

Yeah this was my first time pacing a real person, I need to quit being such a tough critic on myself, just because it looks like it might not be capture when all other signs point to is being capture.

 

[abckidsmom]

It's capture because you have a negative deflection and then a positive wave for the repolarization. You want to see repolarization, which is the indicator that depolarization has occurred.

If you run the milliamps up, the pad can hold some of the energy and be slow to let go of it, making a smear that can look like a qrs.

I tried to draw a pic of this. Hopefu

 

[MSDeltaFlt]

I had a call for a 83 y/o female with SOB. We get there she is not responsive but had adequate RR with diffuse rales and a hx of CHF and heart problems, previous strokes and MI's.

I put her on oxygen because I am getting sats of 65%. I then put her on the monitor and have 3rd degree HB at a rate of 20 and I can't hear a BP.

I pace at 70bpm/50ma and I feel I have got capture even though the QRS looks like "phantom QRS waves". Her b/p comes up and sats come up so treating the patient not the monitor. Still it appears that the underlying rhythm is marching through the paced QRS at where the absolute refractory period should be and this is impossible. My vitals signs increased and I checked the underlying rhythm several times during pacing and it was the same. Any thoughts? Normal paced rhythm has broader QRS and wide T waves, but I treated patient.

Thoughts?

You say her BP came up. To what? If it was at least 90 sys, then you did fine. If it was still low, you probably could have upped the voltage.

Did on those complexes that didn't capture, did she have pulses? If is she did, then you did fine. If she didn't then she could've used more voltage.

Were her symptoms resolved? If They were, good job. If they weren't then don't worry use it as a learning experience. I do everyday. My last cardiac pt (occluded recent stent), should've had dopamine sooner.

 

[rhan101277]

You say her BP came up. To what? If it was at least 90 sys, then you did fine. If it was still low, you probably could have upped the voltage.

Did on those complexes that didn't capture, did she have pulses? If is she did, then you did fine. If she didn't then she could've used more voltage.

Were her symptoms resolved? If They were, good job. If they weren't then don't worry use it as a learning experience. I do everyday. My last cardiac pt (occluded recent stent), should've had dopamine sooner.

Yeah I do the best I can, its medicine and you learn everyday.

BP was 100/65 at destination and she had spontaneous respirations and some hand movement probably to pain, GCS 3 on scene to GCS 6 at destination.

 

[systemet]

My vote is for, you don't have electrical capture, just looking at the ECG.

* You have this very steep negative Q wave, that's not that wide, and you don't have a clear big, broad T wave.

* You have QRS complexes that look exactly like the original unpaced rhythm, including one in second beat that's falling in what would be the T wave, if this was capturing.

If the patient improved, fantastic. The pain and stimulation from the pacer may have caused an increase in sympathetic tone, perhaps.

Did you find out what had happened? RCA occlusion? RVMI?

 

[TomB]

Definitely not capture. The second "phantom" paced cardiac cycle shows the intrinsic rhythm in the absolute refractory period which is impossible. 50 mA generally will not achieve capture on a LP12. At least, not in my experience. I've seen one case where capture was achieved at 80 mA. All others were 90-120 mA. However, you are correct in your suspicion that these complexes show classic false capture morphology (almost vertical downstroke, slight curved return stroke but not particularly wide, and non-distinct ST/T). Don't feel badly. 99% of health care professions in the nation are doing this wrong. That's why I wrote the article at ems12lead.com. Now you know. It takes a lot of guts to stand up and say, "Wow, I missed this because I'm new." (Actually it has nothing to do with the fact that you're new. It's poorly taught and poorly understood.) What I'm saying is, it bodes well for your future as a health care professional.

 

[abckidsmom]

Definitely not capture. The second "phantom" paced cardiac cycle shows the intrinsic rhythm in the absolute refractory period which is impossible. 50 mA generally will not achieve capture on a LP12. At least, not in my experience. I've seen one case where capture was achieved at 80 mA. All others were 90-120 mA. However, you are correct in your suspicion that these complexes show classic false capture morphology (almost vertical downstroke, slight curved return stroke but not particularly wide, and non-distinct ST/T). Don't feel badly. 99% of health care professions in the nation are doing this wrong. That's why I wrote the article at ems12lead.com. Now you know. It takes a lot of guts to stand up and say, "Wow, I missed this because I'm new." (Actually it has nothing to do with the fact that you're new. It's poorly taught and poorly understood.) What I'm saying is, it bodes well for your future as a health care professional.

Well, thanks.

Can you explain how it is that there is a positive deflection? This was a pet peeve of a medical director of mine, and he explained it the way I did above.

Or, I guess, that just doesn't matter?

 

[rhan101277]

While it definitely does not look like classic capture, I had increased sats to 100% and good blood pressure as well as a palpated carotid rate equal to what I was pacing at. This makes me wonder if some false capture morphologies can still be true capture. Maybe the strip I posted wasn't but maybe I had some occasional capture, I am going to recognize this next time.

 

[46Young]

In addition, if you have quantitative capnography, I would expect someone in cardiogenic shock to have a low ETCO2 (low flow > low ETCO2).

When you get true capture, I would expect the number to rise, not unlike when you get ROSC in an arrest, albeit less dramatic.

 

[TomB]

This blog post explains why there is often an increase in BP, improvement in LOC, and even a detectable arterial waveform with false capture:

http://ems12lead.com/2008/11/transcutaneous-pacing-tcp-the-problem-of-false-capture/

Just keep in mind that you cannot have mechanical capture without electrical capture. However, you can have electrical capture without mechanical capture (a sort of "paced PEA" although I suspect that often this is due to low fluid status and a bedside echo would show ventricular contraction).

Here is a post that shows successful TCP with increase in ETCO2.

http://ems12lead.com/2010/12/using-capnography-to-confirm-capture-with-transcutaneous-pacing-tcp/

@abckidsmom I'm not sure what you mean by positive deflection but if you're talking about the pseudo T-wave I think it's a rebound phenomenon. The phantom QRS is actually created by the mA traveling across the combo-pads. The computer filter "closes its eyes" during the transmission of the pacing impulse (otherwise the artifact would shoot off the ECG paper) but often it "opens its eyes" and the tail end of the current creates phantom QRS complexes.

I don't know, but I suspect that placing the limb lead electrodes on the arms and legs (as far as possible from the combo-pads) might help limit this artifact. Another point is that the phantom QRS complexes will "grow" without changing morphology as you dial up the mA. Then, the morphology will change when you achieve true electrical capture.

 

[TomB]

Here's a picture-perfect ECG of TCP with capture (although the patient did not survive).

http://ems12lead.com/2011/02/transcutaneous-pacing-tcp-for-asystole/

 

[abckidsmom]

Thanks. I learned a lot because of this thread and what you are saying makes perfect sense. I don't know what I have been thinking all this time.

 

[46Young]

Thanks. I learned a lot because of this thread and what you are saying makes perfect sense. I don't know what I have been thinking all this time.

This is why I turned bunch of providers at my FD on to EMS12lead.com.

 

[systemet]

Tom's website is excellent. I've learned a lot from it.

Thanks Tom!

 

[rhan101277]

While this is good information and will be remembered, How can you explain a pulse ox reading of 100% if the rate was still 20? I also had a good manual blood pressure measurement. Not saying anyone is right/wrong here.

I know you said the skeletal muscle contraction could cause "wishful thinking" on pulses, but I did get an increase in vital signs and a huge increase in pulse ox.

 

[systemet]

While this is good information and will be remembered, How can you explain a pulse ox reading of 100% if the rate was still 20? I also had a good manual blood pressure measurement. Not saying anyone is right/wrong here.

My opinion -- and it's just that, I may be wrong:

* The initial reading of 65% might be inaccurate. I'm guessing the perfusion at the probe site wasn't that good.

* You're giving her a high FiO2, which might be expected to raise the SpO2 by itself, anyway.

* I think the blood pressure measurement reflects a change in patient condition, and if it's improved the perfusion at the probe site, it will raise a false-low reading on the SpO2. I just don't think that that change is due to a properly capturing pacer.

Just looking at the ECG tracing, I'm certain that the pacer isn't capturing. If there's doubt about this on a call, you can probably look at the pulseox waveform, and see if you're getting pleth complexes corresponding to the paced beats.

I know you said the skeletal muscle contraction could cause "wishful thinking" on pulses, but I did get an increase in vital signs and a huge increase in pulse ox.

But the improvement in the vital signs might be due to the oxygen if she was critically hypoxic? If she's sitting at anything close to 65% when you first met her, she's going to be profoundly cyanotic. And if you end the call at 100%, the difference is going to be night and day. Critical hypoxia also isn't going to help cardiac output any.

Just wanted to add, like Tom said, lots of respect that you're willing to put this case up and discuss it.