Q:

Can submerging into water be used to replace defibrillation?

Many years ago I saw an episode of ER where there was a person who suddenly experienced some heart rhythm problems in the hospital. There was a qualified doctor nearby and a defibrillator, but the latter was dysfunctional because of a drained battery.
So the doctor filled a small bath with water and then with assistance of his colleagues submerged that person's face into water. As they described it, water got into person's nose, irritated nerves located there, his body reflectively assumed it was drowning and that had such a powerful impact that the person's heart resumed normal functioning.
How realistic is that? Does such drowning imitation have enough effect to replace a defibrillator?

A:

I suspect that what happened in that ER episode was a patient who had an attack of tachycardia -- where the heart is beating so fast that it no longer pumps blood efficiently. This particular rhythm can be treated by harnessing the diving reflex. When cold water (specifically below 21 C or 70 F) contacts the face, the heart immediately slows down by 10 to 25%. Thus if the heart rate is too high, this will immediately address the problem. 
(Other effects take place afterwards, as described in the linked Wikipedia article, but the first effect is the relevant one.) 
This is ONLY effective when the problem with the heart is that it is beating too fast. Other arrythmias, such as fibrillation, may not be affected. Thus the need for defibrillators. Fibrillation is irregular and unsynchronized quivering of the muscles. The problem there is not necessarily that the heart is beating too fast, but that it is not beating properly. Defibrillation attempts to reset the rhythm. 
Again, according to Wikipedia, defibrillation is only used in cases of tachycardia where there is no pulse.

A:

Let me try to explain each of those ideas separately.
The ice method is sometimes used as a form of VAGAL STIMULATION which can be done in a clinical setting to reduce heart rate.  It is done when patients are conscious and the electrical conduction of the heart is still able to pump blood to the body.  
In a general sense, it works by stimulating the vagus nerve to slow down the impulse telling the heart to beat.  There are other ways of performing vagal stimulation to slow the heart, such as having the patient blow through a straw, carotid sinus massage, or having the patient attempt to "bear down" as if they were having a bowel movement.  Any of these things can be attempted in a clinical setting to slow heart rate before other, more invasive methods are tried (medications, cardioversion, defibrillation). While vagal stimulation may slow certain varieties of accelerated heart rates (supraventricular tachycardia for example) it is not a substitute for defibrillation.  This is because defibrillation works differently, and on different electrical disturbances.
Defibrillation is only used when the heart is beating in one of two specific rhythms; Ventricular Tachycardia and Ventricular Fibrillation.  In both of these states, the electrical system of the heart is still sending signals which can be observed on an EKG, but they are not adequate to pump blood, so the patient has no pulse.  Basically, at this state the heart is just a quivering muscle which cannot really pump blood in that condition. 
When the heart is in VT or VF, defibrillation is necessary.  Defibrillation works by conducting electricity through the heart in order to STOP it, not to START it.  It works on the principal that the heart is shocked out of the current non-perfusing rhythm with the hope that the body can start it back up again and when it does, it will be in a rhythm that is capable of pumping blood to the body.  
If for some reason defibrillation is unavailable, there is also another method called the PRECORDIAL THUMP.  It is an absolute last ditch move, done by pounding a fist down on the patient's chest, with the hope that the energy transferred from the hit will work the same way defibrillation does.  However, this rarely works.  
TV medicine is usually horribly wrong, for instance: you do not shock a flat line, and there is really no reason to inject "adrenalin" or anything else directly into the heart, but on tv they do it all the time for the drama.  

