First thing we need to mention and get out of the way is "not required implantation".
Having just had a thallium /gamma camera heart scan I got chatting to the consultant in the "wait time" and we got talking about IMD's and the big big population percentage difference in the number of implants in the UK and the US.
Believe it or not something like one third of IMD's put in patients in the US really have no medically discernible benefit, and a around another third have very little medical justification (I need to get access to the paper he told me about to get the actual figures etc).
Thus it would appear that in the US a significant number of people are undergoing a significant medical procedure that has greater short term risk than benefit. Apparently a lot of the reasoning is not based on the risk or benefit to the patient but the risk and benefit to the doctors and insurers involved.
So at the moment this is more germain to the US than other countries, however the likes of Taiwan are rapidly catching up.
It is difficult to get accurate figures for the actual number of patients with IMD's but the "market estimate" for the US is between thirty and fifty million patients and an 8.3 % year on year increase. However I have a feeling the market forecast is all based on one set of market research and regurgitated in many reports so treat the figures with caution.
[google bits of the following phrase to see why I think this,
"US demand for implantable medical devices will increase 8.3 percent annually to $48 billion in 2014. Although weakened in the past few years by product recalls and safety controversies, especially in the cardiac implant segment, growth will remain strong."
So I had to dig around a bit. The upper figure (50million) is based on the number of devices manufactured and the expected life time (20-30years), however some people get IMD's updated more frequently (than others get new cars...). Part of this may well be due to reliability and other issues with some previous designs of IMD's being replaced around a rather low 7years (a little under a third of the expected design life).
The IEEE has a special interest group covering IMD's and one report (ISBN: 978-1-4244-1335-5) from late 2007 indicates it is now a mature market and has had an evolution quite similar to that of Mobile Phone development.
If true then the effective price of IMD's is going to drop fairly quickly to the point where it is insignificant against the cost of the surgery involved. Which will in it's turn bring the price of the surgery down and possibly it's reliability up.
The consequence of this is that IMD's put in next year could still be in a live human in 2040.
Indirect Access Computer Malware in it's various forms was effectively unknown until Win3.11/95 and it only stopped being "egoware" and become sophisticated in the last five to ten years. Would you put a PC with only the original first release of Win95 on the Internet today?
By the way it is not just IMD's where this is a very this long product life -v- poor security is a real issue. Various Bills/laws are being prepared in the name of "the environment" where your electrical appliances will be remotely controlled by the utility companies for a whole host of reasons. The quite predictable outcome of this will be that such devices will be in situ for 20-30years, and that once inplace the power supply networks will quite rapidly become more brtittle and that unless the appropriate security precautions are taken there will be a "major incident" wake up call like that related to drugs packaging and the cyanide laced Tylenol that caused at least seven deaths in the Chicago area back in 82.
Thus one of the reasons given for the increase in IMD being implanted is "patient safety" that is IMD -v- Drugs. This is not just incidents of drugs being either fake or tampered with, it is also as seen with antibiotics that the efficacy of new drugs is diminishing. Another reason is the failure of other passive implants (stents with built in drugs). And the "health care industry cost savings" there are some in the insurance industry that regard IMD's as being the less costly solution when compared to longterm use of expensive drugs followed by surgery with a much higher price, due in part to the rapid rise in the number of people in the US living to over 70 (that is the one off cost of the device and surgery today compared to the cost of 20 years on ever more costly drugs and proportionately much higher cost surgery).
Whatever the reason the growth rate in implantation is expected to be a little under 10% year on year for the foreseeable future and around 10% of the US population already having had two IMD's implanted. It does not take much maths to realize that it won't be to long before having an IMD at 50 in the US will be the norm rather than the exception.
Two of the people (William H. Maisel, Tadayoshi Kohno) who wrote the paper Bruce linked to also wrote an article (behind a pay wall http://content.nejm.org/cgi/content/extract/362/... ) for the New England Journal of Medicine which give a more general overview of what the issues are with IMD's -v- Drug treatment and computer security.
For a more risk oriented view Kevin Fu (assistant professor of Computer Science at the University of Massachusetts Amherst) wrote an article in June 09 for the Communications of the ACM Inside Risks column ( http://www.csl.sri.com/users/neumann/... ).
However neither gives figures for expected number of people to have an IMD implanted over the coming years. Which is a pity as we know the likelihood of something happening goes up with the number of susceptible systems, often geometrically so. That is there is usually a tipping point where the probability becomes a certainty.
As a not so odd turn up for the books it is actually this concern for patient safety (IMD's over drugs) and security of the patients personal privacy with Wireless IMD's in the recent US Health Care Bill that gave rise to scare mongering about,
"Obama Health Care Bill To Include Implantable Microchips In People"
( http://www.puppetgov.com/2010/03/30/... ).
It is without doubt a complex and politically fraught area of medicine within the US and soon will be only marginaly less so outside of the US.