There’s nothing like watching a TV show and seeing medical personnel come in with the paddles (even these are rarely used) to shock a patient. Many people say this is “jump-starting” the heart and this is really the wrong clinical picture to give as far as medical accuracy is concerned. The use of electricity on the heart actually stalls it.
How could that possibly be helpful to a patient?
Heart cells are very unique, cool little contraptions. Each cell in your heart can generate a beat. Yes, that’s right, every little teeny one. Most often, the normal conduction system of the heart overrides this unique property of heart cells, and the electricity flows from the AV node to the SA node so the heart contracts in a normal, orderly fashion.
The heart’s normal beat is important because when the top (the atria) contract, it pushes the remaining blood that doesn’t flow via gravity when the valves open into the ventricles. When the ventricles contract, it pushes blood out to the rest of the body.
The purpose of blood flow is really oxygen delivery to the cells. Of course, there are other functions but this is primary. Without oxygen delivery to the cells, cells will die. Lack of oxygen delivery to the cells is called shock.
We’ll talk more about shock in later posts.
Defibrillation (or unsynchronized cardioversion) is only used in a few arrhythmias. Ventricular tachycardia and ventricular fibrillation. These arrhythmias appear when something has affected the heart’s normal conduction system– such as a heart attack, electrical injury, lack of oxygen. They are more common to the adult population than to the pediatric.
In these arrhythmias, the heart’s normal conduction system is no longer working properly and other cells in the heart become active in an attempt to keep the patient alive. The problem with these arrhythmias is that they do not produce a pulse.
No pulse is clinical death. So, we must get back the patient’s pulse back in order for them to have a chance at survival.
What defibrillation actually does is stop the heart by briefly terminating all electrical activity in hopes that the heart’s normal conduction system will begin to work and a palpable pulse will then ensue.
Important note— there must be some electrical activity for defibrillation to work. So, it is not indicated for the treatment of asystole or when the patient has “flatlined”. This is done often in television shows and is a clear medical inaccuracy.
Electricity is also used in another condition called supraventricular tachycardia (SVT). Supra means above. So this rhythm is a very fast rhythm generated somewhere in the atria. Sometimes, when the heart beats incredibly fast, it doesn’t have enough time to fill with blood. When it fills with less blood, it pumps less blood out. Less blood out means less oxygen delivery. The patient can have signs and symptoms of lightheadedness, dizziness, sweating, chest pain, and difficulty breathing to name a few. They still have a pulse though it may be weak and thready.
The goal of using electricity in this instance is again to disrupt this pathway by stalling it in hopes that the heart’s normal conduction system will take over at a much slower rate.
There is also a medication that can be given that will chemically stall the heart, too. It is called adenosine and is used in the stable patient presenting with SVT. It is used in instances of fast rhythms to slow the pulse down.
Does this change your impression of how defibrillation really works?