Anyone trained in transcutaneous pacing (TCP) needs to be able to identify the rhythm below instantly.
It shows a patient being transcutaneously paced at 80 bpm and 125 mA on a LifePak 12 [the strip is labelled 130 mA but that refers to a point just past the end of the paper, I promise].
Well, actually, it shows attempted pacing. Despite the generous current being delivered there is no evidence of successful electrical capture. Without electrical capture there cannot be mechanical capture, so the patient’s pulse at the moment is only 10 bpm.
Here are the patient’s two native QRS complexes — the only ones generating a cardiac output as a result of his exceedingly slow baseline rhythm.
Though they resemble QRS complexes, the fourteen other “blips” you see on the strip are actually just artifact from the pacer. This phenomenon is commonly referred to as “false capture” and it is a huge problem.
The Problem of False Capture
On November 12, 2008, Tom Bouthillet published an article on this blog that hit me as a revelation and changed the way I approach transcutaneous pacing.
You need to go read it right now. I’ll wait here.
Before encountering that post I had no idea how difficult it could be to achieve and identify successful transcutaneous pacing. Since then I’ve seen dozens of cases of attempted TCP — both in person and shared by colleagues and readers — but very few of them have demonstrated even intermittent capture.
There’s a catch: in most of those cases, the treating providers were absolutely certain they had achieved good capture. Patients woke up; non-invasive blood pressures improves; mechanical capture was confirmed with pulse palpation — but regardless of how confident the team managing the patient was, in almost every case the rhythm strips they showed me were pathognomic of false capture.
Tom turned me into a TCP skeptic and that is in every way a good thing.
I don’t care how strong a patient’s radial pulse feels while they are being transcutaneously paced; you cannot have mechanical capture without electrical capture. And without true mechanical capture, any improvement in the patient’s condition is merely the result of noxious stimuli being provided 60-80 times a minute — often for hours on end. The patient might become more alert, but it is not because their heart rate has increased significantly.
Patients get admitted overnight on ineffective transcutaneous pacing.
While pacing isn’t always a terrible experience if the current is increased slowly and the patient understands what is going on, being shocked all night to zero benefit sounds like torture to me.
Again, for more information on the problem of false-capture and how to identify ineffective pacing go re-read Tom’s article, but what follows is a case that demonstrates false-capture, true-capture, and two objective ways of confirming mechanical capture.
The details of the case are not overly relevant, but let’s say a patient presents quite unwell with a pulse of 20 bpm. No es bueno. Here is his initial 12-lead:
Atropine is administered and fails to improve the heart rate. Time to start transcutaneous pacing. Here’s what we see when we turn the monitor’s Pacer function on.
The current is increased from 0 mA to 10 mA.
The current is increased from 10 mA to 30 mA.
The current is increased from 30 mA to 50 mA.
The current is increased from 50 mA to 70 mA.
The current is increased from 70 mA to 90 mA.
Most providers give up on transcutaneous pacing before even reaching 90 mA; having read Tom’s article though, you know that is a fallacy.
The current is increased from 90 mA to 110 mA.
The current is increased from 110 mA to 125 mA.
Don’t give up yet…
The current is increased from 125 mA to 130 mA.
We finally see a few complexes that demonstrate true electrical capture! Note how the true-capture beats are followed by wide, obvious T-waves, while the false-capture pacer artifacts are only followed by diminutive pseudo-T-waves.
Spurred on by signs of success, the current is increased to 135 mA.
The patient will be leaving the emergency department to go to radiology so the current is increased from 135 mA to 145 to ensure safe capture through the trip. Just before leaving the resus bay a problem is noted though…
What started out as a couple of dropped complexes has progressed to a string of six non-captured pacer spikes… This will not do.
Time to up the current a bit more to 150 mA.
The current is increased to 155 mA…
Not one to give up, you increase the current to 165 mA. Remember: Tom taught us that the monitors go up to 200 mA for a reason — if a patient needs 200 mA to capture and stay alive then that is simply what they need. The rate is also decreased to 70 bpm (just because).
We finally see consistent 100% capture, a pattern which continues through the patient’s trip to radiology and persists over the next hour.
Note that the above strip shows lead II; below are two more strips with the same 100% paced pattern but viewed through leads I and III (just to show how pacing can look different depending on the lead used).
Below is one more perspective of successful electrical capture; this time from a GE DASH bedside monitor.
An hour later, after the patient has stabilized, a change is noted on the monitor.
Success! You’ve supported the patient through his bradycardic ordeal (hitting a lowest-recorded HR of 10 bpm) and now he has resumed a sinus rhythm of his own volition. A 12-lead ECG is captured.
The rest of the patient’s emergency department and intensive care unit courses are uneventful (and his labs, including potassium, unremarkable) and he is discharged back home in healthy condition… with the addition of an implanted pacemaker.
For the sake of brevity today’s discussion only focused on identifying electrical capture. Check out Part 2 of this case where we discuss two objective methods of confirming mechanical capture.
Can’t get enough TCP? As a companion to the original article by Tom, Christopher Watford wrote a second in-depth review examining just why we are programmed to miss false capture so often.
Alternatively, check out everything our blog has written on the topic of transcutaneous pacing.