| MadSci Network: Medicine |
Hello, Chun. I think you may be confusing the pacemaker with some experimental work on artificial hearts and ventricular assist devices.
Pacemakers do not use radioactive substances to generate the power they need - for the relatively small amounts of electrical power that are used to stimulate the heart to beat with an appropriate rhythm, the pacemaker just needs a special battery. Nuclear energy would be too much power for this application, and - yes - it would do much more harm than good to have a small pacemaker to be shielded with a heavy substance like lead.
Here are two sites that have more information on how pacemakers work:
Your Pacemaker and You (Guidant)
Today's Pacemaker Systems (Medtronic)
While the use of radioactive substances was never seriously considered for pacemakers, they were considered for artificial hearts - because the heart uses a lot of power. There were several conferences on artificial heart research about 25 years ago that considered using implanted nuclear power sources to generate the amount of power needed to keep an artificial heart pumping blood for years. As I recall, one of the special sessions discussed an interesting potential problem: what if a whole bunch of recipients of nuclear-powered hearts happened to meet together in the same building, say at some sort of reunion of artificial heart recipients -- could they reach critical mass? (in other words - would we then effectively have a nuclear bomb?).
In any case, nuclear-powered artificial hearts had many issues, such as the ones you mentioned, and have not been used in human beings. Instead, people can receive heart transplants from other people who died but whose hearts are still strong. The first artificial heart was the Jarvik-7, and the power source was outside the body: an external air compressor that powered the pump.
The ventricular assist device (VAD), or artificial ventricle, is an internally implanted pump designed tht does not replace the heart -, but helps pump the blood if the left ventricle is failing . The first portable ventricular assist device was implanted in 1991, and the power source was a battery pack - not any sort of nuclear power.
Here are some sites with more information on artificial hearts and ventricular assist devices:
Encyclopedia.com - Artificial heart
Alternative power supplies for artificial organs
Try the links in the MadSci Library for more information on Medicine.