[JshWright]

Defibrillators are used in cases of ventricular fibrillation and ventricular tachycardia. These are lethal heart rhythms where the heart is either quivering uselessly, or beating too fast to allow the heart to fill with blood between beats. In both of those cases, the patient will have no pulse. A defibrillator will never shock someone who has a pulse (weak or otherwise).

Asystole is when there is no electrical activity in the heart. You are correct that that asystole cannot be shocked, but it definitely won't result in a 'weak' heartbeat (nor should you do CPR on someone with a weak pulse).

[CarpetBench]

> nor should you do CPR on someone with a weak pulse

Absolutely untrue. CPR is recommended by the AHA for anyone who isn't breathing, regardless of whether they have a pulse [0].

By "she may have had a weak pulse", I mean that she may have had a weak pulse that wasn't felt. That's not asystole technically, but it results in the same treatment.

Emergency situations are, understandably, high-adrenaline scenarios and mistakes get made. Even professionals aren't great at detecting carotid pulses properly all the time [1].

> In both of those cases, the patient will have no pulse

Absolutely untrue as well. Only VF is pulseless. VT can present both ways [2].

0: http://circ.ahajournals.org/content/122/18_suppl_3/S640

1: http://www.emsworld.com/article/10320480/the-vital-signs-par...

2: https://en.wikipedia.org/wiki/Ventricular_tachycardia

[JshWright]

Neither statement is untrue... You're absolutely correct that the AHA doesn't recommend a pulse check for lay people. But if you know they have a weak pulse, then clearly you did a pulse check, and CPR would not be indicated.

VT with a pulse is not defibrillated, it is cardioverted. If someone is being defibrillated, they are either in VFib or pulseless VTach. In either case, no pulse. Do not ever, ever, ever defibrillate someone with a pulse.

[CarpetBench]

I hate to get into an internet pissing match, but I think this is important (especially so if you're a healthcare professional, because this obviously has ramifications for you). Still, I really have no desire to argue with strangers on the internet, so this is the last I'll say about this:

Both are untrue.

> But if you know they have a weak pulse, then clearly you did a pulse check, and CPR would not be indicated.

Re-read the AHA guidelines I linked to. CPR is indicated for apnea or agonal respiration. Pulse or not.

You are absolutely supposed to do CPR for someone with a pulse if they aren't breathing, because as you probably recall if you're not breathing your pulse is going to disappear shortly anyway.

> VT with a pulse is not defibrillated

Right. You said (emphasis mine):

> Defibrillators are used in cases of ventricular fibrillation and ventricular tachycardia. These are lethal heart rhythms where the heart is either quivering uselessly, or beating too fast to allow the heart to fill with blood between beats. In both of those cases, the patient will have no pulse.

Which is untrue, as you noted: VT isn't always treated by defibrillation. And, as I noted, VT doesn't always present with no pulse. The distinction is important, because someone reading that paragraph may be confused and think "VT is always treated with defibrillation". Which is absolutely untrue.

[JshWright]

I am a paramedic and an AHA CPR instructor.

We are making orthogonal points...

If someone is being defibrillated, then they have no pulse. The person using the AED may not know that, but the AED does.

You initially said:

> Since they were performing CPR on her, it's likely she had a very weak or no heartbeat (asystole), which defibrillators are no good with.

You seem to be saying that if a person doesn't have a pulse, they must be in asystole, and don't need a defibrillator, which is dangerously untrue. The only reason you do CPR is to preserve the heart and brain long enough to use a defibrillator. In fact, the only circumstances under which someone should be defibrillated are certain types of pulseless cardiac activity.