On 15-6-2009 14:02, Stephen wrote:

> electrical impulses to the heart are interrupted and fibrillation occurs. IIRC
> there are parts of the heart that receive the electrical impulses from the
> brain then transmit secondary impulses to the muscle tissue to contract and
> relax in an organised way. 

No the heart is autonomous, will even beat outside the body for some 
time (hours) if oxygenated. It's frequency can be modulated by stuff in 
the blood and by nerve tissue that is close to the sinus node when they 
release special molecules.

> The electrical shock interrupts this process and you
> get a disorganised high frequency oscillation in different parts of the heart. 

No, but what happens is much more complicated (i.e. you need a 
complicated model to describe it and even then you see it happening 
without getting much more understanding, but it works).
Standard procedure to induce VF in an open chest heart: hold a 9V 
battery against it. And, no, I don't know how it actually works, but it 
does.

> A defibrillator is used to stop this effectively stopping the heart and the
> natural sinus rhythm can be resumed. Before defibrillators became commonplace
> the manual method was to strike the victims chest above the heart with a
> controlled blow using the pinkie side of your fist. This was supposed to have


I does work sometimes. http://en.wikipedia.org/wiki/Precordial_thump Do 
not apply to people that are not in VF: 
http://en.wikipedia.org/wiki/Commotio_cordis

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