isnt it the salt imbalance that shuts the organs down?
The heart's electrical activity depends on there being a gradient between the potassium inside the heart's muscle cells and the blood. If the level of potassium in the blood is too low, the heart becomes too excitable and will develop a dangerous arrythmia, ie: one that doesn't pump blood through the body. If the level of potassium is too high, the heart is unable to beat, hence the use of high dose potassium in lethal injections.
Potassium wasting diuretics (eg: lasix) combined with an unbalanced pre-contest diet can easily result in dangerously low levels of potassium.