Naked Science Forum
Non Life Sciences => Technology => Topic started by: Dave B on 19/11/2013 21:54:43
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Hello, this is my first attempt at a post here so please pardon me if it is in the wrong place.
I'm not a medical technologist, just a retired JOAT lab tech, but I do have a very keen interest in the field.
I have a device implanted called and Implantable Cardiac Defibrillator, or ICD (or "box" to the cardiologists!).
This is a titanium cased device, about the size of a mobile phone, located under the left side of the chest with one to three leads going to the heart. It has a pacemaker function but does a lot more. It can produce and store over 30J of energy at about 800V which is delivered directly to the fibrillating heart. It has a bit of a punch - I know, I have had seven such shocks so far!
But, that alone, from the technology point of view, is interesting - it's all the ancillary stuff that, sort of, takes the biscuit. The device monitors the heart constantly with a sliding recording window. Should any notable event happen this will be captured and stored in RAM. The device is fully programmable in terms of what it does and when. If the heart rate goes over what the call "VT1" (Ventricular Tachycardia 1), 120 pulse per second for more than 16 seconds for me, a synchronising signal is produced to persuade the heart to behave. If it does not do so it gets the 800V slap. Should the pulse rate exceed 180 the slap comes even faster.
I have to say there is no residual pain after the shock, you just pick yourself up and phone for a check-up appointment.
So, constant monitoring and a sliding record. Now we have to access that. This is either done with a pick-up coil on the shoulder or, as in the case of my new one, via a wifi type link. Currently I have to go to the lab for this but there are now home readers that send the data down the line from home available. I may not get one because of a potential hardware problem. Had one of them already - more on that later.
The download also includes of info regarding the physical state of the device, pacing % time, lead resistances, charge times, battery life and other parameters.
My current hardware problem is an increasing resistance on one of the leads. Nasty because this not only reduces the efficiency but can create a hot spot - not what you want in your ticker! The last problem was a battery that headed for being flat, at a very rapid pace, half-way through its estimated life. They should last up to 7 years and the last test said it had 3.5 years left at current usage.
Then, one evening, there was this buzzing in the box - it has a mobile phone buzzer built in that goes off at 10% battery life left. By the time I got on the table for the new one there was not enough energy left in it for a therapeutic shock. The op it normally done under a sedative, but I don't think they bothered this time, I was chatting with the cardiologist and he was telling me what he was up to all the time - we have a good relationship.
The same technology has also been used to help those with Parkisonism, the leads go into the brain and it can be "tuned" to suit the user, by the user once the basic parameters are set. The effect of the therapy is fantastic. There is a Youtube clip of this at https://www.youtube.com/watch?v=h8tWlYv1Ykc (https://www.youtube.com/watch?v=h8tWlYv1Ykc)
Great stuff!
Sorry if this is a bit of an essay but, you can understand, I am all for this kind of tech! So far this device has saved my life twice - my heart recovered just before the shock on the other five times.
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Wow,
7 shocks.
And, hitting you at 120 bpm.
I met a guy with a pacemaker/defibrillator. Apparently the hospital routinely lowers the limits for the defibrillators when a person is admitted to the hospital. And, in his case, they forgot to raise the limits again on discharge. So, one day when he was simply closing a gate, with snow on the ground, he was huffing a little bit, and got slammed with the defibrillator. It scared the daylights out of him, and wasted a trip to the hospital.
I'm not sure if your defibrillator is rechargeable, but theoretically one can recharge the batteries, even with an implantable device.
I don't think the defibrillators are very good at recognizing the difference between ventricular sinus tachycardia and ventricular fibrillation. You should be able to do moderate exercise without being shocked. If you find yourself being shocked with moderate exertion, then you might discuss with your cardiologist whether it is appropriate to get the limits increased. I assume they can test your heart rate, and other parameters on a treadmill.
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Mornin' CliffordK
Wow,
7 shocks.
And, hitting you at 120 bpm.
No, when the shocks occurred my heart was doing more like 200 - 300 bps.
I met a guy with a pacemaker/defibrillator. Apparently the hospital routinely lowers the limits for the defibrillators when a person is admitted to the hospital. And, in his case, they forgot to raise the limits again on discharge. So, one day when he was simply closing a gate, with snow on the ground, he was huffing a little bit, and got slammed with the defibrillator. It scared the daylights out of him, and wasted a trip to the hospital.
Yeah, that happened to me. I wondered why I was feeling so grotty and then I did even worse on the treadmill test. They checked it and my pulse was pegged at 70. Now I am allowed to get to 120 so excercise does not affect it much.
I'm not sure if your defibrillator is rechargeable, but theoretically one can recharge the batteries, even with an implantable device.
They have not told me that this new model is rechargeable - but I doubt it. The size of any induction coil that allowed more than a daily very low level trickle charge would increase the size somewhat. Having said that I am told that the next generation may have GPS and a mobile phone function that can call for help and report the person's location when things get nasty!
I don't think the defibrillators are very good at recognizing the difference between ventricular sinus tachycardia and ventricular fibrillation. You should be able to do moderate exercise without being shocked. If you find yourself being shocked with moderate exertion, then you might discuss with your cardiologist whether it is appropriate to get the limits increased. I assume they can test your heart rate, and other parameters on a treadmill.
Quite! But since it seems VT can change to VF quite quickly it makes sense to hit the VT first. There is that attempt at re-synching, "ATP", Anti Tachychardia Pacing before the shock. But, if the shock returns the heart to "normal" who worries?
As someone old enough to remember when the transistor was first announced at the Earl's Court Radio Exhibition and there were three kinds, Green Spot (RF), White Spot (audio "power") and Red Spot (GP) on the public market I am vacillate between amazement and acceptance (simply because of the ubiquity of the gear) of modern electronics.
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Mornin' CliffordKWow,
7 shocks.
And, hitting you at 120 bpm.
No, when the shocks occurred my heart was doing more like 200 - 300 bps.
Hopefully not "per second".
However, it is difficult to get a "normal" heart rate above 200 bpm, which means the defibrillation could have been life saving.
I suppose the question is whether the defibrillators can recognize the difference between heavy physical exertion, and an abnormal beat (perhaps leading to V-Fib).
Anyway, dead battery or not, I'm glad the technology has been life saving. I was reading that the rechargeable systems haven't been widely adopted yet, but with the frequent episodes, perhaps you would be a candidate (in another 3 years).
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. . . but with the frequent episodes, perhaps you would be a candidate (in another 3 years).
Oops on the bps! Yikes!
Well, if they are ready when and if I need a new lead . . .
As you say, 200bpm is not an efficient rate for the heart which is why one often faints at the time. There is a built in delay now so that I faint before the shock. Not that the shocks really bother me, had worse when working on high power transmitters in the RAF. 20kV was my max, faulty insulation on an eht insulation tester (irony rules, OK). Threw me backwards through a door which I took off its hinges! Rather painful.
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Here is an article about device longevity. (http://content.onlinejacc.org/data/Journals/JAC/23042/02077.pdf)
For the devices they tested, the lifespan was 3-5 years for a "standard" battery, and on average a couple of additional years for the extended life battery.
The article seems to indicate that there may be an economic incentive to make disposable devices rather than rechargeable devices, or devices with replaceable batteries.
Of course, the surgery is not insignificant.
Perhaps it will take organizations like Medicare to push for longer lifespans on the devices.
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I see the title has changed . . . I was hoping others might add ideas/experiences of other med. tech. but - no matter.
Yes, CliffordK, seven years is the expected life of the units I have had. I was told that each shock takes about a month of the life. I also have to assume that figure also includes the 98% pacing that my unit is doing, if the pacing was not constant that would extend the life.
I think it is "commercial" rather than "economic" regarding rechargeable units! It would be economic in the big picture not to have to change the device during the recipient's life, but that would mean a reduced income for the manufacturers.
It seems that there is an organisation recycling pacer units from deceased patients that still have at least 70% of their life left. Not sure if this will extend to ICDs, but they can be used for pacing only if need be. The manufacturers do not like this at all it seems! ;D But the chances of them getting a large market in India for the prices they charge is slim. By the time Indians can afford them they will probably be making their own - or buying them cheap from China.
The surgery has dangers of course but it is not that invasive in fact, bit more than a keyhole job but not massive. Getting the leads into the blood vessels and heart without doing damage, and then sealing them, is more critical.