CAPTURE — Cardiac And Pacing Training Using Realistic Emulation

A temporary transvenous pacing simulator for ICU/CCU medical and nursing staff.

▶ Run it: https://ectope.github.io/capture/

⚠️ Simulation for education only — not for guiding patient care

This is not a medical device and is not validated for clinical use. It must not be used to guide the care of a real patient.

• Confirm everything locally. Every threshold, interval, safety margin and procedure here is a teaching approximation. Check it against your own unit's policy and the manual of the generator you actually use. Devices differ. Where this simulator and your local policy disagree, your local policy is right.
• It is an adjunct, not a replacement. It is a teaching aid, meant to be used alongside experienced clinical instruction, with a supervisor in the room who can correct it. It is not a substitute for that instruction, nor for supervised practice on the real device.
• The device is generic, modelled on a typical dual-chamber external pulse generator rather than any particular manufacturer's. Some scenarios depend on features a given box may not have — Scenario 10 (cross-talk) assumes no ventricular safety pacing, which many temporary units lack but some do not.
• The physiology is simplified: it simulates cardiac timing and events, which is the level at which pacemaker behaviour operates. It is not a cellular model.

The simulator can tell you what a box does. It cannot tell you what a patient needs.

index.html is entirely self-contained — no server, no build step, no network. It can equally be downloaded and opened straight from disk, which is the point: it runs on a locked-down ward machine with no internet.

The scenarios implement tvp_simulator_script.md, a structured teaching script that doubles as a validation checklist. Every "Expected simulator behaviour (✓)" checkpoint in that script runs as an automated assertion — see Tests.

Two modes

Sandbox — pick the underlying rhythm openly and play with the box.

Teaching — pick a scenario instead. The rhythm and the patient's capture thresholds are hidden; the trainee has to work them out with the device, which is the whole point. Each scenario carries its vignette, its objectives and an instructor-only debrief. Some carry clinical actions — roll the patient, put the pads on, treat the potassium — that are not dials on the box.

Scenarios follow tvp_simulator_script.md, and all twelve are implemented: Tier 1 (1, 1b, 2, 3, 4), Tier 2 (5, 6, 7, 8) and Tier 3 (9, 10, 11, 12).

Features

• VVI, AAI and DDD pacing, with an ASYNC switch (VOO / DOO / AOO)
• Simulated ECG with pacing spikes; arterial trace coupled to mechanical capture
• Underlying rhythms: sinus, heart blocks, asystole; junctional or idioventricular escape foci, or none at all (the pacing-dependent patient)
• Adjustable rate, upper rate limit, AV interval, PVARP, outputs and sensitivities
• Fault modelling: failure to capture (static, jittering, or rising in real time), under- and oversensing, output failure from a broken circuit, cross-talk, lead displacement with ectopy and septal perforation, retrograde VA conduction and pacemaker-mediated tachycardia
• Transcutaneous backup pacing as a rescue pathway
• Deterministic: scenarios use a seeded PRNG, so they look irregular but replay exactly — which is what makes them fair to assess against

Local Development

pip install -r requirements.txt
python app.py

Then open http://localhost:5000

index.html is self-contained and also works opened directly from disk, with no server.

Tests

node test_scenarios.js          # teaching scenarios; no browser, no deps

Runs each scenario's "Expected simulator behaviour (✓)" checkpoints from the teaching script as assertions against the simulator's internal cardiac event stream.

# sandbox rhythm x mode matrix (needs Playwright + a running server)
npm install playwright && npx playwright install chromium
flask --app app run --port 5050
BASE_URL=http://127.0.0.1:5050 node test_pacing_behaviour.js

Deployment

Configured for Render.com deployment via render.yaml.

Licence

CAPTURE © 2026 Tim Bowles, licensed under CC BY-NC-SA 4.0.

Please use it. Copy it, run it on your unit, write your own scenarios, retune the values to match your own generator, translate it. Three conditions:

• Credit — attribute it to Tim Bowles and link to the licence, and say if you changed anything.
• Non-commercial — teaching your own staff, running departmental or regional training, and using it in university courses are not commercial uses. Selling it, paywalling it, or bundling it into a commercial training product are.
• ShareAlike — if you build on it, release your version under the same licence, so improvements stay open.

If you adapt it, you take on responsibility for the clinical accuracy of your adaptation, and you must not represent it as validated for clinical use. Please keep the safety disclaimer.

LICENSE is the full legal code; NOTICE is the plain-English summary and the clinical disclaimer.