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your mouse over the numbers to learn more.
Capacitors
Similar to the ones
used in camera flashes, capacitors can take up to 10 seconds to draw enough
energy from the battery for a large jolt. Charge times for smaller shocks are
much shorter.
Leads
Flexible wires convey sensing information to the I.C.D. and carry electric shocks
to the heart. A patient may receive one or two leads depending on the nature
of the heart problem. They are covered with silicone insulation.
Memory
The pattern of heart activity
before, during and after
disturbances is recorded.
Casing
The I.C.D. is encased in titanium. Scar tissue grows around it, locking it in
place. The device is sealed shut to prevent leakage, so when the battery dies,
the entire device must be replaced.
Connectors
A lead with three connections provides sensing capabilities and a pathway for
high-energy shocks to one of the heart’s lower chambers. A second lead
with only one connection provides sensing and pacing to an upper chamber.
Transformer
For serious heart disturbances requiring a higher shock, a transformer converts
low-voltage battery power into a higher voltage.
Antenna
Communication between the I.C.D. and the programmer is made through low-frequency
radio waves sent from the unit's antenna to a doughnut-shaped receiver held
over the patient's chest.
C.P.U.
The processor chip analyzes electrical signals from the heart and determines
whether any shocks are necessary. The chip runs at less than 100 kilohertz,
making it more energy efficient.
Battery
The special batteries, made of lithium silver vanadium oxide, last six years
or more, even though they have less energy than a standard laptop battery.
Beeper
A warning beeper indicates a low battery or another problem that a doctor should
check out. There are no warnings to signal a large shock to the patient.
