A short course in pacing:  when the heart beats erratically, the dysfunction is in the sinus node, which causes contractions with electrical impulses to the heart muscle.  The first pacemakers took over the pacing--and some still do, if the natural regulator's failure is serious.

It became possible, however, to build pacers which can also sense (through input leads from the muscle) the body's charges, and step in only when the rhythm falters.  This closes the medical loop between dysfunction and remedy--a doctor in the house.

Implantation, miniaturization and programmability are stories in themselves, but the closed loop is at the center of what Medtronic does (leading the industry, pacing beyond pacing).  The sinus node, for instance, adjusts heart beat in response to stimuli from all over the body, and as biochemistry understands them more fully we can learn to read them with sensors and enrich the loop to more closely approximate the physical system.

This has been done with full-time pacers which, until recently, beat at a constant rate.  Since they did not quicken in response to an increase in physical activity they restricted wearers to the nonstrenuous.  A crystal-tipped lead implanted in the chest in an attempt to read breathing rate unexpectedly picked up vibrations from all over the body--closing the loop and easing the restriction on lifestyle.

The Drug Admistration Device is another loop.  Implantable, it will read, for instance, glucose level for a diabetic and administer insulin in response.

Medtronic makes it possible to say without fear of contradiction that Minnesota leads the world in medical technology.  The.  World.  Leader.