What problems can defibrillators fix, and why can’t we use them with all cases? Why is there, apparently, a time limit on their use for a patient?
In: Biology
The actual electrochemical system of the heart is a little bit beyond eli5, but in short, basically our heart has an electrical system (essentially using charged chemicals in place of electrons moving through metal). That electrical system is how the heart times (“paces”) and transmits (“conducts”) beats. That signal can be generated in a few places called “pacemakers”, and the signal conducts along predefined routes (almost like natural wires) through the atria and the ventricles. This ensures that the heart contracts in the proper sequence and at an appropriate rate.
Now, there are certain very specific instances where the electrical system goes haywire…situations where for whatever reason, the electrochemical transmission system has malfunctioned. If someone gets an electric shock, that’s one example where the heart often was simply jolted out of rhythm, and can be jolted back to a proper rhythm again. Another case is where somebody might have drowned for a short time, and the heart is “stunned” but not dead.
What we see more often clinically are a few things….cases where a person has an abnormally-firing part of the heart, a rogue cell that decides to take over pacemaking, and a defibrillation essentially sends a “hard reset” to the heart, hopefully stimulating a synchronized beat again. Sometimes a person has a pulse and is even awake, but the electrical system has gone haywire (either due to chemical imbalances, long-term damage to the system from high blood pressure and such, much smaller heart attacks that haven’t done too much damage but have messed with the electrical system, etc), and so we do what’s called “cardioversion”, which is like a softer, specifically timed defibrillation. (Extra info: often that involves atrial malfunctions, such as atrial tachycardias and atrial fibrillation, but can occasionally include ventricular malfunctions, specifically ventricular tachycardia with a pulse).
The other time we use it is when people are pulseless, i.e. clinically dead. People often associate that situation with heart attacks, rightly so, but defibrillation is only occasionally useful in those cases. Heart attacks usually involve death of the heart muscle…and even if the electrical system works fine, dead muscle can’t pump. In some cases, there’s enough of viable heart tissue left, but that tissue has been “stunned” due to lack of oxygen, and hopefully a defibrillation, in combination with some CPR, oxygen and medications, can un-stun and resynchronize it. That’s the whole idea. In some cases, this wasn’t due to a heart attack, but perhaps somebody who has lost a lot of blood and got to a trauma center clinically dead, but the heart muscle hadn’t quite died yet, and the blood loss was emergently corrected. (Extra info: Those shockable situations are usually ventricular fibrillation, and occasionally ventricular tachycardia).
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