Without evidence of benefit, an intervention should not be presumed to be beneficial or safe.

- Rogue Medic

Potentially Reversible Causes of Cardiac Arrest – Arrhythmia

In my last post, Not Successful Resuscitation, I mentioned the potentially reversible causes of cardiac arrest. First a definition. These are conditions that can lead to sudden death as well as a more gradual death. In the case of a more gradual death, their potential for reversibility dramatically decreases. One of the reasons is that these conditions, conditions bad enough to kill you, can cause significant organ damage when they are present for an extended period. Acidosis is very destructive to the body, but if it is a sudden change, rather than a long term condition (especially one that is not responding to aggressive medical treatment), then reversing the acidosis may help to resuscitate the patient.

Why only may?

There are many factors that affect the ability to resuscitate a patient. As I mentioned, a gradual onset is not as easy to reverse. A gradual onset is because the illness is a chronic condition or a progressive condition.

But if it is a progressive condition, that has progressed to death, how can it be a reversible cause of cardiac arrest?

The potentially reversible causes tend to be sudden. That does not mean that a gradual onset rules out resuscitation, just that it becomes much more difficult to resuscitate these patients, and much more difficult to keep these patients alive if we do manage to resuscitate them. These causes tend to be overwhelming to the body. Still, a sudden onset of a potentially reversible cause of cardiac arrest may not respond to treatment, even if the patient is in the ideal treatment setting, because these causes are only potentially reversible.

Then why spend so much time on them?

All of resuscitation is about potentially reversible causes. VF/Pulseless VT (Ventricular Fibrillation/Pulseless Ventricular Tachycardia) are the easiest to reverse, the most likely to be reversed, and the easiest to diagnose.

Diagnose? Paramedics can’t diagnose.

Of course you can. You just can’t legally claim that you are diagnosing. This is purely a legal distinction. It has no basis in reality.

Arrhythmia – shocking a shockable rhythm.

Some of the arrhythmias that can cause cardiac arrest may be reversed by defibrillation. Some of the arrhythmias that can cause cardiac arrest will not improve with defibrillation. Asystole is an excellent example of an arrhythmia that will not respond to defibrillation. Asystole is caused by defibrillation. We shock patients because we want to cause asystole – temporarily.

The defibrillation is designed to send enough current through the heart to stop the heart for less than a second. The purpose of defibrillation is to get rid of the dangerous rhythm that is controlling the heart, whether it is an organized rhythm, such as VT or SVT (SupraVentricular Tachycardia), or disorganized activity, such as VF.

After the shock is delivered, and some asystole is produced, it is hoped that the heart starts again on its own and when the heart starts again, it is hoped that the sinus node will be controlling the rate and rhythm. If the patient’s normal pacemaker is not the sinus node (a couple of examples are atrial fibrillation or an implanted pacemaker), then the hope is that the normal pacemaker resumes its role of initiating a rhythm capable of keeping the patient alive.

In western movies, during a big bar fight, the sheriff may fire a gun into the air. Everyone tends to stop, at least long enough to make sure the gun is not pointed at them. This pause in the commotion is what defibrillation is supposed to accomplish. The sheriff is telling the arrhythmia to move along. As in the movies, it does not always work as planned. If the arrhythmia/chaos does not go away with defibrillation, more defibrillation may be attempted. Even if the ceiling is shot full of defibrillations, there is no maximum number of defibrillations, as long as the patient is in a shockable rhythm. Antiarrhythmic medications may be added to the treatment (after some epinephrine, the most arrhythmogenic drug we use). The search for other potentially reversible causes of cardiac arrest will contribute to treatment.


Something that causes arrhythmias. I describe problems with the use of epinephrine in Epinephrine in Cardiac Arrest, More on Epinephrine in Cardiac Arrest, and Dead VT vs Not Quite Dead, Yet VT.

What if the asystole is not temporary?

This is not unusual. The current ACLS (Advanced Cardiac Life Support) algorithms are pretty easy to use.[1] If you are using an algorithm that no longer applies, you should switch to the algorithm that does apply. I will cover asystole in another post.

Are there any other rhythms that should be defibrillated?

SVT – if the patient is pulseless. Any rhythm that would be cardioverted, if the patient were alive, should be defibrillated if the rhythm is bad enough to produce a dead patient. Although this falls into the category of PEA (Pulseless Electrical Activity), it is a shockable rhythm and will respond best to defibrillation.

One of the perversions of the algorithms is that they spend almost no time on Postresuscitation Support. There is no algorithm, flow sheet, or other easy to use chart. The 2010 ACLS Guidelines added an easy to use algorithm.[2] This is the AHA (American Heart Association), in the 2000 guidelines they were not discouraged by the possibility of an overly dense, extremely confusing 3 page tachycardia algorithm “overview” flow sheet. Pages 1, 2, and 3, followed by the individual pages for specific tachyarrhythmias. Fortunately they did learn from that, but there is still no algorithm to ease recall of postresuscitation care – something that is not well understood. That will be more than another post.

There are methods of determining if the arrest is one that may be reversed by treatment. Again, this is something for another post.

That is enough of the potentially reversible causes for this post. And I haven’t even started on the list of potentially reversible causes. 🙂

The PALS (Pediatric Advanced Life Support) potentially reversible causes of cardiac arrest list is 5 H’s and 5 T’s:

Hypovolemia; Hypoxia; Hydrogen ion (Acidosis); Hypo/Hyperkalemia; Hypoglycemia; Hypothermia.

Toxins (Drugs); Tamponade, cardiac; Tension pneumothorax; Thrombosis (coronary or pulmonary – AMI or PE); Trauma

I have changed this from what I originally wrote. My, borrowed from Jeff B of JB on the Rocks, mnemonic (memory aid) for the potentially reversible causes of cardiac arrest is now two words – COLD PATCHeD.

COLD reminds you that the C is for hypothermia – being very cold, sometimes we forget the obvious in resuscitation attempts, so it doesn’t hurt to put extra reminders in a mnemonic. O for Oxygen deficit or hypoxia. L for Lytes. This works better as a mnemonic for the in hospital crowd, but there is nothing wrong with getting EMS to think more about electroLytes. Hypokalemia and Hyperkalemia – too little and too much potassium. D for Drugs (OverDose, poison, wrong drug, wrong dose, . . .).

PATCHeD = PPE (Pulmonary Embolus); A Acidosis and AMI (Acute Myocardial Infarction); T Tension Pneumothorax; C – Cardiac Tamponade; H – Here it is still confusing, a whole bunch of Hypo’s and one Hyper. The Hypo’s: HypoVolemia; HypoThermia; HypoGlycemia; HypOxia; HypoKalemia; The Hyper: HyperKalemia; e – Everybody dead gets Epi. Just a reminder to continue CPR and other treatments. D Drugs (OD, poison, wrong drug, wrong dose, . . .); Distributive Shock.

I will have to write a post on why each of these categories matter, what the treatments are, and other ways to approach them, rather than the order of the mnemonic. This is a lot for one post.


[1] 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science
Volume 122, Issue 18_suppl_3;
November 2, 2010
Guidelines index

Below is the link to the old guidelines:

2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care
Volume 112, Issue 24 Supplement;
December 13, 2005
Guidelines index

[2] Post–cardiac arrest care algorithm.
2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care
Part 9: Post–Cardiac Arrest Care
Systems of Care for Improving Post–Cardiac Arrest Outcomes
Algorithm in JPEG format

Part 9: Post–Cardiac Arrest Care
2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care
Free Full Text From Circulation with link to Free Full Text PDF Download

Part 7.5: Postresuscitation Support
2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care
Free Full Text From Circulation with link to Free Full Text PDF Download

Footnotes were added 5/11/2011 to include links to 2010 ACLS guidelines. Links were also updated.



  1. The easiest was to reverse cardiac arrest?Stay away from WAWAs!

  2. How do EMS providers survive in places without WaWa?

    I worked in 2 other states, before working around WaWa. At 92 the WaWa used to close at 23:00. 🙁

    The question is, which is more dangerous, walking through the parking lot or eating the food?


  3. I use COLD PATCH rather than Hs/Ts…Cold (hypothermia), Oxygen deficit, ‘Lytes, Drugs, Pulmonary Embolus, Acidosis, Tension Pneumo, Cardiac Tamponade, Hypovolemia.

  4. Jeff B,

    I like COLD PATCH. It helps to break up a lot of the Hs that I end up with in PATCHeD. As I continue this, I will go over that, too. With a second H for Hypoglycemia, which is why I use the PALS causes.


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  6. Taylor1940,

    Thank you.



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