ECG Patient Simulator.
Date: November 14, 2020
Design: Johan Smets
A very useful tool for everyone who has to deal with ECG monitoring.
Don't forget to check the useful Tip at the end of this page.
The ECG Patient Simulator.
Every anesthetist or nurse in an OR or in a recovery room regularly deals with it:
"My patient is connected to the monitoring system, but there is no signal on the monitor or why am I only seeing noise? Are the cables, making a poor contact? Is it a bad connection in the adhesive electrodes? Is it the monitor device that's not working? What is going on?"
It can become a long search to find the cause of the problem. The adhesive electrodes on the patient are often difficult to reach when the patient is covered with sterile drapes. Lotion the patient used before and is left on the skin, the use of certain medication, or a heavier person can still cause an unsatisfying ECG signal even when the electrodes have been changed. It could be a defective cable or a moisture problem in the connections. Despite the reliable equipment, it could still be the monitor that is not working, and so on, and so on......
As long as there is no usefull signal available for testing, it can become a frustrating hassle before a decent ECG signal appears on the monitor. After all, the ECG is a very small signal, ideally between 1mV and 3mV peak-to-peak. Little interference from external factors can already result in a poor or unusable signal.
In that case, the ECG Patient Simulator is a grateful tool.
A 3- or 5-lead ECG grabber cable can be connected to the ECG Patient Simulator in the same way as if it were connected to a patient. Instantly you can begin to diagnose the cabling starting from the electrodes to the monitor without bothering the patient or surgeon too much. When the Simulator is connected to the monitor using the ECG cable(s), and an ECG wave is visible on the monitor, only a poor electrode contact with the patient can still be the cause of a bad or missing signal after reconnecting the patient.
Can it get any easier ?
Commercial ECG Patient Simulators are available with a price tag of a few thousand to tens of thousand euros. These are devices from renowned brands are calibrated and can, in addition to generating an ECG signal, also simulate clinical anomalies and perform other functions.These devices can be used by a Biotechnical Service or by certified service technicians to perform maintenance and calibration of medical equipment within a hospital. In that case, the price is certainly justified. However, to locate a bad connection or obtain a GO/NO-GO test from a monitor, an ECG Patient Simulator as described here is more than sufficient.
The FLUKE Prosim8 Professional Patient Simulator.
Am I again minimizing my own project?
I guess, but for a compact device like this and for the price of less than € 50, it contains a ton of possibilities but we'll get to that later.
Our ECG Patient Simulator generates an ECG signal as we can expect with a perfectly connected patient. The 3 main leads, I, II and III, and the three augmented leads aVL, aVR and aVF are produced by electrodes R, L, F. The precordial lead V1 is formed by electrode V1 and the average of the 3 main leads, and the N electrode is reference or noise suppression. All leads are neatly simulated with an amplitude of up to about 3 mV for the strongest lead (lead II).
On our ECG Patient Simulator you will find these connections R, L, F, V and N, that fit on the electrode grabber clips of a standard ECG grabber cable. When testing a 5-lead configuration, all 5 clips are connected to the simulator. When testing a 3-lead configuration, only the R, L and F clips are connected, while V and N remain disconnected.
After switching on the simulator, it generates an ECG signal with a heart rhythm of 60 beats per minute (BPM) by default. The BPM can be increased or decreased with both push-button. The heart rate is indicated on the device by an LED and a beep tone. Because troubleshooting with our ECG Patient Simulator rarely takes longer than a few minutes, the device switches itself off after 5 minutes. When a series of cables should be tested at the technical service shop, the simulator can be switched on for a period of 30 minutes by simultaneously pressing the "-" and "ON / +" keys. This automatic power-off function is intended to save the 9V battery. Additional options are shown in the following specifications or can be found in the quick reference of the device.
If you don't want to spend much time on designing a housing for this device, you can download all parts for a 3D printable casing in the download area of this project. I chose to make the housing as compact as possible so that it can be printed on one of the smallest 3D printers, the Velleman Vertex Nano.
The 3D printed housing holds the printed circuit board, the speaker and the 9V battery. The signal shape on the front of the case is a 3D printed inlay of transparent PLA. This will light up by the LED at the rate of the selected BPM.
A 3D printed housing as an example. It houses the printed circuit board, the speaker and the 9V battery. The signal shape in the front is an inlay of printed transparent PLA. This is lit by the LED to the beat of the selected BPM. The eye wants something too.
What are the possibilities of this device with its 5 connection pins and only two push buttons?
- On / Off switching by the double function "ON / + " push button.
- Increase or decrease heartrate by pushing the "-" or "ON / + " push buttons.
- 8 heart rhythms selectable in steps of 30 BPM:
30, 60, 90, 120, 150, 180, 210 and 240 BPM (Starts up at 60BPM).
- Auto shutdown selectable after 5 minutes (default) or 30 minutes.
- Rhythm indication by a bright LED and clear BPM beeps.
- BPM Beep tone can be switched on or off by setting internal DIP switch.
- Notification of switched-on device by means of a discreet beep when the BPM beep is turned off.
- Start-up tone selectable by setting internal DIP switch.
- Adjustable amplitude of the ECG signal from 0mVpp to 3mVpp:
- Automatic adjustment of amplitude across all BPMs.
- Battery level monitoring by changing the startup tone and beep tone.
- Emergency startup possible with (almost) empty battery.
- Powered by a 9V rectangular battery.
A golden tip while solving ECG cable problems:
ALWAYS REPLACE ALL PARTS OF AN ECG CABLE AT THE SAME TIME!
In many cases, the cable from the monitor to the patient electrodes consists of two parts. A first part is the 3- or 5-Lead grabber cable that is connected on one side to the patient electrodes and on the other side to the second part of the cable, namely the 3-5-Lead extension cable. This 3-5-Lead extension cable is then connected to the monitor. The two parts are connected by means of connectors. When moisture gets between the connectors, due to a spilled fluid during the procedure or due to an overzealous cleaning service that washed the cables with just a little too much cleaning product, often a strong disturbed or even no signal will show up on the monitor.
If you are troubleshooting and you want to replace the wiring from the monitor to the patient, always replace all parts at the same time. When you replace piece by piece, in order to find the defective part of the cable, it is very likely that you wet the first dry (new) part of the cable with the wet (old) part and then you wet the second dry (new) part of the cable with the first, now also wet, (new) part. Eventually you will end up with a cable of which both parts are new but still connected using wet connectors! In other words, both parts will wet eachother again!