EEVblog #656 - Pacemaker Monitor Teardown - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: August 27, 2014, 07:41:52 am
content: What's inside a dial-in pacemaker monitor system?Datasheets:LMV824http://www.ti.com/lit/gpn/lmv824MAX4330:http://datasheets.maximintegrated.com/en/ds/MAX4330-MAX4334.pdfCNY64 Optocoupler:http://www.vishay.com/docs/83540/cny64.pdfADSP-2185N DSPhttp://www.analog.com/static/imported-files/data_sheets/ADSP-218XN_SERIES.pdfCX88168 Smart Modem with Voice CODEChttp://pdf.datasheetcatalog.com/datasheet/Conexant/mXrqvxu.pdfMAX994 10bit ADChttp://datasheets.maximintegrated.com/en/ds/MAX985-MAX994.pdfMeder Reed Sensor:http://www.meder.com/fileadmin/meder/pdf/en/Products/Reed_Sensors/Reed_Sensor_MK06_E.pdfProbe Shock Video:!Private video

author: German_EE
author_rank: Super Contributor
timestamp: August 27, 2014, 09:06:55 am
content: Thank you Dave, just what was needed. Elsewhere on the forum someone has posted their design for an ECG front end and now perhaps they can see what is involved when the job is done properly:1) Medical grade transformers and opto-isolators to isolate various sections.2) Medical grade power supply (the isolation on these is > 4000V).3) Wide gaps in the groundplane between sections.4) High value power resistor in series with each wrist sensor.5) Everything over-engineered because as Dave pointed out an electrical connection across the wrists needs a bit of thought.

author: maartenva
author_rank: Newbie
timestamp: August 27, 2014, 09:21:58 am
content: a demo video

author: Juun
author_rank: Newbie
timestamp: August 27, 2014, 09:54:40 am
content: Would be very interesting to investigate, if they bothered to implement some form of encryption.

author: EEVblog
author_rank: Unknown
timestamp: August 27, 2014, 10:33:33 am
content: Quote from: maartenva on August 27, 2014, 09:21:58 amI didn't think to search youtubeNo ECG on that model, and no human at the other end of the phone...

author: G7PSK
author_rank: Super Contributor
timestamp: August 27, 2014, 10:45:42 am
content: St. Jude medical is not a hospital it makes medical equipment so there could be tens of thousands of those devices out there.The finger design on the pcb inside the coil housing looked like an antennae of some sort.

author: jancumps
author_rank: Unknown
timestamp: August 27, 2014, 11:05:02 am
content: Yes, it's a big company.In Belgium their office is in the same compound as where I work. I didn't have a clue that they work on such cool devices.

author: JackOfVA
author_rank: Unknown
timestamp: August 27, 2014, 11:29:24 am
content: Quote from: G7PSK on August 27, 2014, 10:45:42 amLooks more like a Faraday screen or shield to me -- it reduces electrostatic / capacitive coupling between the pacemaker's internal loop and the monitoring device external loop. The result is only inductive coupling.Jack

author: EEVblog
author_rank: Unknown
timestamp: August 27, 2014, 11:35:21 am
content: Quote from: JackOfVA on August 27, 2014, 11:29:24 amYep, must be that.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 27, 2014, 12:10:43 pm
content: Quote from: JackOfVA on August 27, 2014, 11:29:24 amProbably a shield and/or capacitive coupling as a reference for the other probes - the shape may be to reduce eddy-current losses detuning the coil, which would be a problem with a solid plane.

author: max_torque
author_rank: Super Contributor
timestamp: August 27, 2014, 01:11:48 pm
content: I assume being connected to an external phone line AND directly to a human at the same time is a proper designers nightmare! I mean, get a lightning strike on the line at the wrong moment and you're gonna have to find a nice path to ground before it gets to the person being "treated".............I bet the testing and certification are fun, wonder if they do destructive testing? ie current meter on the wrist straps, plug in a fake phone line, Zapp say 50kV onto that "phone" line and see what the meter reads etc??

author: RupertGo
author_rank: Regular Contributor
timestamp: August 27, 2014, 02:42:00 pm
content: Interesting that the power connector seems to be a standard barrel type. My CPAP machine has a fairly standard brick SMPSU, but the DC connector is something I haven't seen anywhere else - I assumed so that there was no danger of plugging in the wrong PSU. (As I have approximately ten thousand wrong PSUs here, the chances of that are quite high)I'd only quite like to see that dual wristband electrode configuration being made compulsory for people leaving comments on YouTube, with a 'vote to apply 5kv' backchannel... I'd grudgingly allow it to be current-limited.

author: coppice
author_rank: Super Contributor
timestamp: August 27, 2014, 03:07:44 pm
content: Quote from: German_EE on August 27, 2014, 09:06:55 amThose big resistors are there for high breakdown voltage, not high power handling.

author: PChi
author_rank: Frequent Contributor
timestamp: August 27, 2014, 03:53:46 pm
content: Quote from: mikeselectricstuff on August 27, 2014, 12:10:43 pmI agree, I have worked on Metal Detectors for the food industry that had the same arrangement. The PCB copper fingers had similar spacing without the nice curves. The PCBs were much larger and were laid out using tape, this was over three decades ago. The frequencies used were in the 100 to 500 kHz region.

author: electronic_eel
author_rank: Regular Contributor
timestamp: August 27, 2014, 08:18:05 pm
content: Hi Dave,would you mind to tear down the power supply too?I guess it is a classic flyback, but I'm wondering if they have any Y-caps between the hot side and output in a medical device like this. And if not, what they do to pass emc tests.Thanks.

author: Maxlor
author_rank: Frequent Contributor
timestamp: August 27, 2014, 08:30:38 pm
content: Interesting video, thanks.A couple of points I'm wondering about. Like, why do you need the wriststraps? Pacemakers measure internal ECGs (or IEGM), and they'd have much better signal fidelity than what you'd get from the wrist straps. Granted, they'd also measure along a different axis (the axis matters a lot with ECGs) but I would expect the leads with their measurement points to be positioned in such a way as to deliver the signal relevant for that specific patient?Measuring an ECG with wrist straps has some drawbacks, for example, you'll pick up any activity of your chest and arm muscles, it'll show up as noise on the ECG which can easily be an order of magnitude or two larger than the signal you're trying to measure. In my experience, something as simple as speaking makes the ECG signal unusable. I would expect that even just holding the coil in place would also not work, therefore I expect the patient to use the device while lying down, or maybe way back in a chair, so the coil rests in place on its own, and the patient trying to relax his chest and arms as best he can. I imagine the doctor will also tell them to shut up for a couple of seconds while the ECG is being recordedI imagine that this might also be the reason why they put some effort into the speaker and microphone, so that it's usuable with the patient lying a meter next to it, as opposed to speaking directly into it.Those same kind of coils are used to actually program the pacemaker. I wonder whether they do remote programming with that device. I suspect that while they technically can, they don't do it; the ramifications if anything goes wrong are potentially dire, noone wants to take responsibility for that.I also wonder what kind of data rate you can actually get with an inductive coupling setup like that. Maybe the reason for the wrist straps is that it's too slow to transmit a live IEGM directly from the pacemaker. It will probably transmit recordings of "interesting events" though. Another reason for the wrist straps I can think of is that it's actually the back channel for the implant. They do transmit signals that way as markers, i.e. very short pulses that don't have any effect on the heart, but show up as vertical lines in an ECG. This remains from the days when implants didn't send out any data wirelessly. Thinking a bit more about it, this might be it, because then this system becomes compatible with a whole load of legacy pacemakers.As for those two unopened pacemakers: I would totally expect the battery to still be live, those last a long time. I haven't checked the model numbers, so please, Dave, make sure that the one with the 4 screws isn't actually an ICD. If it is, be very careful; those things charge up to 800V and deliver around 40J, and while it shouldn't do that once explanted and without any signals being fed into it, you never know. It won't be dangerous I think, unless you've got some heart condition, but it'll probably hurt a lot in any case. Oh and the devices I've seen so far weren't potted on the inside, one reason would be that the battery might change slightly in size over time, and potting might crack or put undue stress on some other component. Besides, the welded titanium case provides a hermetic seal. If you have the right equipment to measure it, you might find that the gas inside isn't air. Don't expect too much from opening it though: it'll most likely just be folded flex boards with chunky passives, a naked custom die or two, the battery and (if it's an ICD) a large capacitor stack.The other device with the 16 contacts probably isn't a cardiac device actually. It looks more like a nerve stimulator used for chronic pain therapy. With those, the leads have pads with many (4, 8, 16, 32, thereabout) contacts on them, and they're inserted into your spine, resting next to your spinal nerves. Sending out a high frequency AC signal will stop the nerves carrying pain signals from working properly, the pain wil be replaced by a soft buzzing feeling. The many contacts are used to lessen the requirements of exact positioning (or account for after-implantation shifts); you'll typically only have 2 electrodes activated, but you can change which 2 on the pad to maximize the effect and minimize unwanted side effects.

author: dwayne
author_rank: Newbie
timestamp: August 27, 2014, 10:22:52 pm
content: Hi Dave,The two "pacemakers" you showed are actually neurostimulators, used for pain relief. They both are made by Medtronic, a competitor of St. Jude (both are headquartered in the Minneapolis area). They look very similar, using the same cans, etc.In the St. Jude Housecall device, the coil in the disk receives the information from the pacemaker. This might include: the current programming, event history, and maybe an internal EKG. The disk probably also includes a magnet to let the pacemaker know it is in position. It doesn't send, for the reasons mentioned by Maxlor.Dave W. (worked for Medtronic back in the day)

author: NickS
author_rank: Unknown
timestamp: August 27, 2014, 10:34:21 pm
content: In there I saw at least two components which looked like regular chip capacitors, but with 4 leads one in each corner.What on earth are they?

author: EEVblog
author_rank: Unknown
timestamp: August 28, 2014, 01:38:24 am
content: Quote from: Maxlor on August 27, 2014, 08:30:38 pmAs someone pointed out, they aren't pacemakers, but spinal stimulators.http://professional.medtronic.com/pt/neuro/scs/prod/prime-advanced/

author: DrSchweizer
author_rank: Newbie
timestamp: August 28, 2014, 07:08:06 am
content: Hi DaveI don’t have a pacemaker but I am a cardiologist that loves electronics.We use these devices as you mentioned for home-monitoring of patients but usually not those with a pacemaker but those with an internal defibrillator (ICD). Newer devices report any events (serious arrhythmias or delivered therapies (overdrive pacing or electric shocks)) at a certain time every night (wire less) to the manufacturers database and we cardiologist are then informed by mail or sms. The device you tore down is an older device that was use in about the way you described it.Any more questions?Thanks for the great work and everything I learned from you.I plan to send you some stuff from Switzerland, I just have to get it to Australia. One of the girls in my office is on her way to Sidney so ...Regards-Schlomo

author: German_EE
author_rank: Super Contributor
timestamp: August 28, 2014, 10:09:05 am
content: I have a question about pacemakers. Dave said a couple of times that the pacemaker is placed in the chest but I have also heard that the unit is fixed to the shoulder blade with a wire run to the heart. Which is correct?

author: EEVblog
author_rank: Unknown
timestamp: August 28, 2014, 10:29:04 am
content: Quote from: DrSchweizer on August 28, 2014, 07:08:06 amCool, thanks for the info.There isalwayssomeone in the audience who works in the field, whatever it happens to be!

author: VK5RC
author_rank: Unknown
timestamp: August 28, 2014, 11:08:55 am
content: @German_EE Typically a pacemaker (or implantable defib / pacemaker they are bigger with more complex electronics ) are placed just under the skin below the clavicle (collar bone ) on the left side in front of the chest cavity i.e. external to the ribs, the wire/s are then tunnelled under the skin into the subclavian vein (behind the clavicle) which is then fed along the vein into the Superior vena cava then into the heart (right side chambers).I also am a physician (Consultant General Physician) who has an interest in electronics!

author: yvesdm3000
author_rank: Newbie
timestamp: August 28, 2014, 11:31:46 am
content: Their belgian department seem to be in 2 buildings further next to where I'm sitting, so jancumps you must be close too ! (number 7, 5th floor). :-)Nice that they make (or at least sell) that stuff.-Yves

author: jancumps
author_rank: Unknown
timestamp: August 28, 2014, 11:51:15 am
content: Quote from: yvesdm3000 on August 28, 2014, 11:31:46 amNumber 3, second floor

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 28, 2014, 12:05:50 pm
content: In case anyone missed it - implantable defib teardown :

author: babysitter
author_rank: Frequent Contributor
timestamp: August 28, 2014, 07:14:57 pm
content: And I am a electronics technician in medical device business, doing very little design with vanilla stuff but non-design-supporting in really interesting projects

author: VK3DRB
author_rank: Super Contributor
timestamp: August 29, 2014, 01:53:59 pm
content: Quote from: G7PSK on August 27, 2014, 10:45:42 amAntennasis plural for an electrical antenna.Antennaeis plural for an insect's antenna.

author: VK3DRB
author_rank: Super Contributor
timestamp: August 29, 2014, 02:42:03 pm
content: The PCB lacks of some component designators and almost no semiconductors have pin 1 markers on the PCB. A component level debug technician would probably not be impressed, especially if there were bottom side components as well. Other than that, it looks well designed.The board would be Probably built to IEC 60601-1 Ed 2 or Ed 3.A bit more about designing medical devices in general...Design is very stringent. Everything is documented to the extreme, and regulatory body audits are commonplace. Often, component suppliers are requested for details that are not published in datasheets. After product release, simply changing one component or one line of code usually means the device requires full verification and validation testing. And with the software, unit testing is mandatory for class B and class C medical products, which usually DOUBLES the software development effort. Furthermore, the cost of compliance testing is severe. Medical trials are needed too. Hence development is generally very slow (taking years) and is costly. This development environment of often intense.Typically there must be TWO means or patient protection on a medical device. In addition, earth leakage and touch currents limits are much more stringent than for consumer equipment. One example of higher standards is designing in an old RJ-45 type wired ethernet port. Your common 1.5kV isolation ethernet magnetics used in PC's don't cut it. Typically 4kV isolation medical grade ethernet ports are required. There are a few companies selling these as add-ons (also called network isolators) at very high prices to simply provide the necessary safely isolation between the medical equipment and the unknown wired ethernet network.I know of a medical device designed with a complex array of discrete logic in 1988. The device is still sold today. The vast amount of discrete logic and A/D circuity could be replaced with one small modern microcontroller with relatively simple software. But because of the cost of re-compliance testing, it is still the same as it was in 1988, even with its antiquated design low capacity NiMH batteries.