So you wanna write a medical professional using a defibrillator

It’s my first blog post!


A bit of low-hanging fruit here. This has been written about, a lot, all over the internet, but it’s an error I continue to see on the regular in basically any media featuring a medical professional. Even Dr. Strange got it wrong (among several other things which I might write about in the future). So, here it is:

TL;DR: Thou shalt not defibrillate (“shock”) asystole (“flatline”)


The heart has an internal pacemaker which sets its rate and rhythm by sending electrical impulses across the entire organ. When the electrical impulses are abnormal, an arrhythmia exists. There are many, many types of arrhythmias. The most famous one is asystole, or the “flatline.” You may have seen asystole before. It looks like this:

asystole drawing
asystole (artist’s rendition)

(Usually in TV or film this is accompanied by a long *beeeeeeeeeeep*. And then someone shouts “CODE BLUE!” and a team rushes in, headed by a doctor who grabs a pair of electrical paddles, shouts “CLEAR!,” and *ker-chunk zap*s the patient back to *beep… beep… beep*ing life).

Here’s the problem. Asystole is the total lack of electrical activity in the heart (as perceived by the EKG). The purpose of the defibrillator is to, basically, halt electrical activity so that the heart can (maybe) resume a normal rhythm. You can’t stop nothing. It’s like trying to divide by zero.

What a patient in asystole really needs is CPR.

“But,” you might say (or if you don’t like me putting in words for you, imagine someone else said it), “defibrillation is a real thing, and really saves real patients who look really, really dead. So, what gives?”

I will explain.

Concept 1: The electrocardiogram (ECG or EKG)

The EKG is a visual depiction of electrical activity as it flows through the heart. When it is normal it follows a regular rhythm (the *beep.. beep.. beep..*), with peaks and valleys “mapping out” the flow of electricity through the various heart chambers.

You have definitely seen this before. A normal one looks like this:

ekg waveform drawing
normal EKG “beat” (artist’s rendition)

Concept 2: Fibrillation

There exists a particularly nasty arrhythmia termed ventricular fibrillation. Basically, the electrical activity of the heart has gone totally off the rails. It looks like this:

vfib drawing
ventricular fibrillation (artist’s rendition)

When this haphazard electrical activity is present, movement of the heart muscle becomes uncoordinated. The normal heart contracts (squeezes) in a predictable, regular fashion. Blood enters, flows through, and leaves. The electrical activity coursing through the heart muscle organizes this mechanical behavior. In ventricular fibrillation, the mechanical “pump” that is the heart cannot fill, or contract, appropriately. The heart becomes a quivering, useless thing. It is no longer beating the way it should.


Please note that what I have descried is NOT the same as asystole. In asystole, the heart does nothing at all.


Concept 3: Defibrillation

Let’s look at the word. We are adding the prefix “de” to “fibrillation.” The debfibrillator is intended to shut down the uncoordinated electrical activity of the heart, so that the heart’s innate pacemaker can resume the proper *beep beep beep* rhythm.


So how can you do it better?

If you wanna write a character who is a competent medical professional, but also want that dramatic “CLEAR!” moment, here are some things you can try:

  1. The medical professional could notice that the patient has an arrhythmia called ventricular fibrillation, which looks like uncoordinated electrical activity on the EKG (see images above)
    • Alternatively, the medical professional could notice an arrhythmia called pulseless ventricular tachycardia (not discussed further in this post)
  2. The medical professional could attempt the application of an external defibrillator
    • Other types of defibrillators do exist, and their use depends on context
  3. The medical professional will shout “CLEAR!” prior to applying the electrical current. Why do they do this? To make sure that all parties present are not touching the patient, and ALSO not touching any metal object that the patient is touching (eg a stainless steel table). If someone continues to touch the patient, the electrical current will travel into their body too. Oops!
    • If, for some reason, the medical professional and the patient (and the room?) are all soaking wet, they should also avoid being in touch with the same puddle of water the patient is touching
      • Why would this be? I don’t know. Maybe the hospital is flooding? Maybe the patient is a merperson?
  4. In my experience, the patient’s EKG is unlikely to go directly from *beep.. beep.. beep..* to *beeeeeeeeeeeeeeeeep* (if you’re choosing to go with asystole) or *?!!!!!!!!!!?!?!?!?!!!!!!* (my interpretation of ventricular fibrillation). Often there will be a progression of less severe electrical abnormalities first (such as extra beats that shouldn’t be there and don’t fit the rhythm, sudden increases or decreases in heart rate, abnormal appearance of the electrical activity, etc). The medical professionals could notice this and attempt interventions before things get worse.
  5. If the patient’s heart is successfully returned to normal electrical activity, consider whether there might be after-effects. The patient may remain unconscious, have damage to organs that temporarily lost proper blood flow (such as kidneys or brain), or continue to suffer effects of the disease that made their heart stop working properly in the first place. This all depends on the cause of the problem, and how quickly it was corrected.
  6. In between uses of the defibrillator, CPR should be performed on the patient


Further reading

Take a look at this excellent post on another blog which covered this topic before me (and better than I did). It’s an excellent post which also gives a lot of suggestions about how to write a physician dealing with an actual flatline, and how to write about CPR (cardiopulmonary resuscitation).

Or try Wikipedia

Or these resources that discuss in more medical detail:

The Electrocardiogram (EKG or ECG)

Normal sinus rhythm


Ventricular Fibrillation

I also like this much more detailed Gizmodo article on the subject


Disclaimer: My experience is in veterinary medicine but I am confident that the basic tenants described above are conserved in human medicine. Specific details may vary. For example, certain causes of fatal arrhythmias may be more common in veterinary patients than human patients, or vice versa. Physicians also often have more fancy tools than veterinarians do.


Another disclaimer: None of this is medical advice! See your physician or veterinarian if you have health questions about yourself or your pet 🙂

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