Automated External Defibrillator: The Heart Rhythms it Cannot Shock

Imagine that you witness someone suffer cardiac arrest; you rush to get the automated external defibrillator (AED) and apply it to the victim as you've been trained. However, after the analysis is complete, the AED delivers a no shock indicated (NSI) message. Is the unit working? What is wrong and what should you do?

Pulseless Electrical Activity and Asystole: The Dreaded Nonshockable Heart Rhythms

When an AED delivers a no shock indicated (NSI) message, rarely is anything wrong with the unit itself if it has been properly maintained and is charged. If you have followed proper procedures, it is also highly unlikely that anything has gone wrong with the analysis. As high as 20 percent of victims in cardiac arrest will present with a nonshockable heart rhythm known as pulseless electrical activity (PEA). Remember, the heart has its own electrical system and also relies on mechanical pumping activity to do its job. A PEA is a condition in which the electrical rhythm of the heart is relatively normal; however, the mechanical pumping action is not responding to that normal rhythm or stimulus. A terminal illness or the loss of too much blood are two conditions that can cause PEA. A terminally sick heart might not be able to pump in response to even normal electrical activity and in the case of life-threatening blood loss, there isn't sufficient fluid to pump. Pulseless electrical activity is one of the heart rhythms that is not shockable; therefore, use of an AED will prove ineffective.

I was an emergency medical technician (EMT) student doing my clinicals in the emergency room when I saw a patient with PEA for the first time. I remember hearing the nurse's comments regarding the tense voice in which the paramedic spoke over the radio as he gave his report. Within minutes we could hear the siren and see the lights as the ambulance arrived; we had just finished preparing a room and everyone involved in taking over care was in position. Our 56 year old male patient could not be revived.

Asystole is another nonshockable heart rhythm which occurs in 20 to 50 percent of individuals who suffer cardiac arrest. When the natural electrical system of the heart fails to generate electrical impulses, it is called asystole and is also one of the dreaded nonshockable heart rhythms. Like PEA, asystole can also be the result of a terminally sick heart and severe blood loss. It can also be brought on if ventricular fibrillation, also known as v-fib, is not treated; ventricular fibrillation is shockable. Cardiac arrest victims with asystole have no pulse, do not breath, and are unconscious. Although the heart might be able to perform mechanical pumping action, the organ is not generating any electrical impulses to stimulate pumping. Remember, an AED does not take the place of the natural electrical system of the heart; rather, it can correct an abnormal rhythm in that system if that rhythm is shockable.

How to Help Someone With PEA or Asystole

So, what can you do to help someone in cardiac arrest with one of these nonschockable heart rhythms? First and foremost, do not give up. Don't turn the AED off or remove the pads from the patient. Just because you received a no shock indicated message after the first analysis doesn't mean that you'll receive the same after the second or third analysis; therefore, all hope is not gone. Immediately begin CPR. If you haven't been trained in conventional CPR which includes rescue breathing, perform hands only CPR; calling 911 goes without saying. The AED should automatically analyze again after two minutes; if the victim still has a nonshockable rhythm, all you can do for them is CPR.

Source:

National Registry of Emergency Medical Technicians (NREMT) certification, state EMT license, professional work experience