Teaching Transcutaneous Pacing: Capture, Thresholds, and How to Simulate It

By the X·Sim team · Updated July 10, 2026 · 6 min read

Transcutaneous pacing (TCP) is the most under-trained skill in the ACLS toolbox. It comes up rarely, so providers get almost no live reps — and when the unstable bradycardia finally shows up at 3 a.m., the most common real-world failure isn't forgetting the button. It's believing you're pacing when you're not.

The one concept that matters: capture

Pressing "start pacer" makes the device fire. It does not make the heart respond. That gap is where patients get hurt, and it has two layers:

Electrical capture

Every pacing spike is followed by a wide QRS complex and a T wave. Spikes marching through the underlying rhythm without a QRS after each one = no capture, no matter how confident the monitor looks. The fix is almost always the same: turn the current up.

Mechanical capture

Electrical capture with no pulse is still failure. Confirm a palpable pulse (or better, a pleth/arterial waveform or EtCO₂ improvement) that matches the paced rate. Femoral pulse beats carotid here — pacing makes chest-area muscle twitch that fools fingers at the neck.

What current should students expect?

Typical adult capture thresholds run roughly 40–80 mA, and patient factors (chest wall, positioning, ischemia) push it higher. Two teaching points fall out of that range:

Starting at 20 mA and quitting at 40 doesn't treat anyone. Teach students to step the output up deliberately until every spike captures, then add a small safety margin above threshold.
Sedation is part of the skill. Effective TCP hurts. A plan that doesn't include analgesia/sedation (per local protocol) is incomplete.

Demand vs fixed mode — the sneaky failure

In demand mode, the pacer inhibits itself whenever it senses an intrinsic rate faster than its set rate. Students set the pacer to 60, the patient's escape rhythm wobbles around 65, nothing paces, and the class stares at the screen wondering if it's broken. That's not broken — that's the device working, and it's exactly the kind of thing students should meet in simulation before they meet it on a patient. (Fixed mode paces regardless; it's the fallback when sensing is unreliable.)

The errors instructors should hunt for

Student error	What it looks like	The teaching moment
Spike worship	"We're pacing!" at 30 mA with spikes and no QRS	Show them capture vs non-capture strips side by side; make "spike ≠ capture" a mantra
No pulse check	Electrical capture declared, nobody touches the patient	Mechanical capture confirmation is a required scenario step
Rate set below the escape rhythm	Demand pacer inhibited, team confused	Set pacer rate meaningfully above the intrinsic rate
Atropine tunnel vision	Repeated dosing in an infranodal 3° block while pressure falls	Wide-complex 3° block rarely answers to atropine — pads early
Forgetting the patient hurts	Capture at 70 mA, patient grimacing, no sedation discussion	Analgesia/sedation belongs in the algorithm

How to simulate TCP honestly

Most cheap simulations give students capture the moment they press start — which trains the exact overconfidence that hurts patients. A realistic TCP simulation needs three behaviors:

A capture threshold. The instructor sets the mA at which this patient captures (say, 70). Below it: spikes without QRS complexes. At/above it: paced complexes with a perfusing rate.
Demand-mode inhibition. If the intrinsic rate beats the set pacer rate, the pacer holds off — and the monitor should say so.
A patient that responds to real capture only. Perfusion (pressure, pleth, mentation in the narrative) improves when capture is achieved — not when the pacer merely starts.

In X·Sim: instructors set the capture threshold per case (e.g., "captures at ≥70 mA"), demand-mode inhibition is modeled, and scenario rules can key off real capture — the case's "patient improves" transition fires when capture is obtained, not when the pacer is switched on. The built-in unstable-bradycardia sample case (3° AV block, hypotensive, atropine scripted to fail) runs this exact lesson in about 5 minutes. Try the monitor free or see instructor plans.

A 10-minute TCP station plan

2 min: Strips on screen — capture vs non-capture. Name the difference out loud.
5 min: Run the unstable bradycardia case. Let atropine fail. Watch who steps the current up past threshold and who confirms a pulse.
3 min: Debrief from the action log: time to pads, mA at capture, was sedation mentioned?

X·Sim (xsimlab.com) is an education and training tool — not a medical device — from Brickell Bay Group LLC. Pacing care must follow your medical direction and current AHA/ERC guidance; thresholds cited are typical teaching ranges, not clinical targets.