Hazardous Voltages

[Mark Amundson]

Tim Cockram wrote:
> >>Interesting discussion.  The "hand in the pocket trick" can be a life
> >>saver as the most critical path is left arm right leg (for the 999 in a
> >>1000 whose heart is in the left side of the chest).

> >1 out of a 1000 people have their heart on the other side of their chest???

> It's true that circa 1:1000 people have the heart in the right side of
> the chest (according to an MD who taught me phisiology at university,
> personally I haven't done any tests though). Regards Tim

To be technically correct, the human heart tends to be centered in the
chest but the apex of the ventrical (lower) chambers points to your
lower left side. Tall skinny people tend to have more of a downward
pointing heart for fairly intuitive reasons. Your brain is the pacing
device of the heart and is electrically connected to the right atrium
(upper right chamber) at a place called the sinus node. From there, the
electrical signal propagates through the heart muscle towards the
previously mentioned apex. Thus there is a upper right to lower left
direction of electrical stimulation. An Electro-cardiogram (ECG)
typically will show three pulses per heartbeat with the middle one being
greatly taller. The first one is sinus pulse (atrium), followed by the
large ventricular pulse, followed by a third pulse indicating muscle
relaxation (refractory).

A shock delivered across the hands through the chest may not be
necessarily worse than a shock from hand to foot. The timing of the
shock maybe what matters most. If you endure a shock during the
ventricular muscle contraction (big ECG pulse), you may not have any
effects. A premature pulse while the heart muscle just finished a beat
may initiate ventricular fibrillation (quivering) possibly resulting in
poor circulation (blood flow) and brain death due to lack of oxygen in
the blood. That is why paramedics try to "defibrilate" via another
external shock a victim back to life. Like drowning victims, the task is
to regain oxygen back into bloodstream before serious brain damage.

Some people exhibit slow heart (bradycardia) or fast heart (tachycardia)
due to natural heart defects or through heart muscle damage usually via
blocked heart muscle arteries (a heart attack). For these people, an
implantable pacing and/or shock device is used. Take good care of your
heart.

Mark Amundson
Principal Design Engineer
Cardiac Pacemakers, Inc. (Guidant Corp.)
And diy synth fan