What Are Shockable Rhythms On An AED?

When we think of an AED being utilized, we picture dramatic hospital tv shows where patients have beeping machines with flat lines on the monitor and a doctor yelling “clear!” before delivering a shock. In those situations, the doctor knows what to do with the AED and when to deliver a life-saving shock. But there isn’t always a doctor around in an emergency and cardiac arrest can happen anywhere, not just in hospitals or medical facilities. This means it is very important to understand how an AED discovers a shockable rhythm in a patient and the difference between those and non-shockable rhythms. 

Understanding the Heart 

To understand what shockable rhythms for AEDs are, we first need to know the basics of the heart. The heart is the hardest working muscle in the body pumping over 2,000 gallons of blood a day to move oxygenated and deoxygenated blood throughout the body. This sophisticated pump is composed of 3 systems - - electric, mechanical, and hydraulic. Each system performs a vital job and if one system undergoes issues, the whole system is compromised. 

The mechanical system is the actual muscle contracting the heart to circulate blood through the body. There are four chambers working together to squeeze and contract blood. The hydraulic system controls the fluid (blood) that fills the heart. Blood moves oxygen to and from the lungs where the carbon dioxide is removed and oxygen is added. The electrical system provides energy to the pacemaker cells around the heart, allowing it to pump. These pacemaker cells fire electrical impulses that keep the heart beating and regulate the heart rate, controlling how often the heart beats. The heart typically beats around 80 beats per minute which makes around 100,000 times a day. That's over 3.3 billion beats in a typical lifetime! 

What is Sudden Cardiac Arrest?

When a sudden cardiac arrest occurs, there is a malfunction in 1 or more of the 3 vital systems in the heart. Identifying the system that is having an issue and treating it as quickly as possible is key. The most common problem is an electrical system malfunction in the heart. When this occurs, the heart muscles stop contracting and blood is no longer being pumped throughout the body to vital organs. This causes the organs to suffer damage or die, depending on how much time they are without oxygen.

Some common reasons for sudden cardiac arrest are: 

  • Coronary artery disease
  • Heart tissue scarring 
  • Heart medications 
  • Cardiomyopathy (thickened muscles in the heart) 
  • Congenital heart disease 
  • Long QT syndrome
  • Medication side effects 
  • Electrolyte imbalances 
  • Drug use

What Does an AED Do? 

Understanding what an AED does and what the device is looking for is a great insight when providing treatment. Most AEDs can analyze a patient's heart rhythm and can decide if a shock is necessary. This life-saving shock acts as a restart to shut down the heart and hopefully allow the heart to restart to the original correct rhythm. The shock is sort of like a reset button for the pacemaker cells to restore the electrical signals to the correct rhythm again. 

Shockable VS Non-Shockable Rhythms

Heart rhythms are classified into 4 types, including two of which are shockable with an AED and two that are not. When AED electrode pads are placed on a patient, the AED begins to detect and analyze any heart rhythms present, deciding if a shock is advised or not.

What are Shockable Rhythms? 

Shockable heart rhythms are abnormal heart rhythms that are caused by an aberration in the heart's electrical conduction system.

There are two types of shockable rhythms that an AED can identify to help save a life:

  1. Ventricular fibrillation (V-fib)
  2. Pulseless ventricular tachycardia (V-tach) 

Ventricular fibrillation or V-fib for short is disordered quivering of the ventricles inside the heart. The ventricles are not fully contracting and are similar to a seizure in the heart. The quivering of heart muscles is not enough for a full contraction, only some muscle movement but no actual heartbeat. 

The second type of rhythm is pulseless ventricular tachycardia or V-tach. Typically the heart receives impulses from pacemaker cells and beats in a normal fashion. In pulseless ventricular tachycardia, the pacemaker cells do not receive the signals. Without these impulses, and in order to save the body, the cells decide to fire on their own to pump blood to the brain and body. When the cells create their own signal they fire much faster than they typically should, causing the heart chambers to improperly fill and decreasing blood flow to all parts of the body. After vapid firing, the pulse will eventually stop. 

Both ventricular fibrillation and pulseless ventricular tachycardia heart rhythms have a chance of being restarted and set back to the correct heart rhythm with an electrical shock from an AED and effective CPR. But if the patient has a pulse, a shock should not be administered, so be sure to check the victim's pulse beforehand.  

Non-Shockable Rhythms 

Sometimes the electrical system of the individual body is working properly but other systems  like a mechanical or hydraulic system fail. These hydraulic and mechanical issues can not be treated with a shock. The two types of non-shockable heart rhythms are

  1. Asystole 
  2. Pulseless electrical activity (PEA) 

Pulseless electrical activity (PEA) is a hydraulic system issue, such as blood loss, typically from trauma or internal bleeding. This means the heart's electrical rhythm is beating correctly but there is not enough blood in the body to circulate. An AED shock will not be able to fix this condition as the patient needs more blood instead of a restart of the electrical system. 

Another cardiac emergency that does not require a shock is asystole. This is a complete absence of electrical activity in the heart. This is what we see most commonly portrayed on TV with flat-line monitors. With no electrical activity in the heart, there is no rhythm to restart. A shock would not be advised and CPR and medicine would be the best form of treatment. 

AED Shockable Rhythms

Sudden cardiac arrest can happen anywhere at any time and it is important to be ready. The best action you can take if you see someone in cardiac arrest is to grab an AED as quickly as possible and attach it to the patient. The AED will identify one of the 4 types of heart rhythms (ventricular fibrillation, pulseless ventricular tachycardia, asystole, and pulseless electrical activity) to determine if a shock is advised or not. 

Regardless of what the AED says or does, you should always call 911 as soon as possible. Providing treatment to an individual as quickly as possible will increase their chances of survival.  Understanding what an AED is looking for in heart rhythms brings a deeper understanding of sudden cardiac arrest emergencies, the severity, and what steps to take moving forward to try and save a life.

To learn more about AEDs check out our website or give us a call at 1-800-441-8378.