IEEE Spectrum November, 2008 - 28

IdIot
proofing
the Defibrillator

A

t its best, the human heart is a supple machine. When the
hydraulics work as they should, an electric current rhythmically moves blood through the heart's four chambers. Electric
impulses travel along specialized fibers and then dart from
cell to cell, causing the muscle fibers to contract and relax
as regularly as a second hand ticking around a clock face. When
they contract, the muscle fibers create high-pressure regions
that push open the heart's valves. Blood pours out of one
chamber into another, and just ahead of the blood travels
the current, methodically exciting the right fibers and
cells in sequence.
But when things go wrong, that current can incite
incredible chaos. If a heart is stricken by ventricular
fibrillation-a common type of cardiac arrest-then
its once-orderly conduction devolves into a scattering
of impulses. These impulses travel through the heart
as little wavelets, causing unsynchronized tightening
and releasing of the muscle fibers in the ventricles, the
two lower chambers of the heart. Without synchronization, blood flow ceases; starved of oxygen, other organs
rapidly begin to fail. Within 10 minutes, the victim will
almost certainly die.
About one-fourth of all deaths in the developed world can be
attributed to cardiac arrest-an astounding figure, and one that now
has a chance to drop, in no small part because of the automated external
defibrillator. AEDs are designed to shock a heart that's in ventricular
fibrillation back into a healthy rhythm. The device is now so easy to use
that even an untrained bystander can administer this time-critical and
highly effective medical procedure. AEDs, which fit into a case the size

40

NA * iEEE SpEctrum * NovEmbEr 2008

jason lee

how a device
that shocks a failing
heart back to life
became one of the
greatest engineering
success stories
in medicine
by mark W. Kroll,
Karl Kroll &
byron Gilman

www.spectrum.ieee.org



http://www.spectrum.ieee.org

Table of Contents for the Digital Edition of IEEE Spectrum November, 2008

IEEE Spectrum November, 2008 - Cover1
IEEE Spectrum November, 2008 - Cover2
IEEE Spectrum November, 2008 - 1
IEEE Spectrum November, 2008 - 2
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IEEE Spectrum November, 2008 - 41
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IEEE Spectrum November, 2008 - 45
IEEE Spectrum November, 2008 - 46
IEEE Spectrum November, 2008 - 47
IEEE Spectrum November, 2008 - Cover3
IEEE Spectrum November, 2008 - Cover4
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