Understanding What Shockable Rhythms Are on an AED

AED shockable rhythms are abnormal heart rhythms that require defibrillation in order to restore normal heart rhythm. Defibrillation is a medical procedure that uses electric shocks to reset the heart’s rhythm back to a normal rhythm. AEDs, or Automated External Defibrillators, are used to deliver the shock. 

What Are the Different Types of Shockable Rhythms in AEDs?

Shockable rhythms are abnormal heart rhythms that can be treated with a defibrillating shock from an AED. The two types of shockable rhythms that can be treated with a defibrillator are ventricular fibrillation (VF) and pulseless ventricular tachycardia (V-Tach). 

What Is Ventricular Fibrillation (VF)?

Ventricular Fibrillation (VF) is a life-threatening heart rhythm disorder that occurs when the ventricles of the heart quiver instead of contracting in a normal, steady rhythm. This chaotic quivering of the heart muscle prevents the heart from pumping blood properly, leading to cardiac arrest. VF is the most common cause of cardiac arrest and sudden cardiac death. 

Ventricular fibrillation is caused by abnormal electrical activity in the heart. In a healthy heart, electrical signals travel through the heart in a specific pattern, causing the heart muscle to contract and pump blood. In VF, the electrical signals become disorganised and chaotic, so the ventricles quiver instead of contracting. This causes the heart to stop pumping blood and disrupts the normal flow of oxygenated blood to the body.

What Can Cause Ventricular Fibrillation?

 Ventricular fibrillation can be caused by a variety of factors, including heart disease, trauma, drug overdose, or a heart attack. In many cases, the exact cause of VF is unknown and is referred to as idiopathic VF. In some cases, VF can be caused by the presence of an underlying heart condition, such as an arrhythmia, coronary artery disease, or cardiomyopathy.

Certain medications, including certain antiarrhythmic and antihypertensive drugs, can also increase the risk of VF. Additionally, certain medical procedures, such as cardiac catheterisation, may increase the risk of VF due to the manipulation of the heart muscle.

What Is Pulseless Ventricular Tachycardia (V-Tach)?

V-Tach is a type of arrhythmia or abnormal heartbeat. It is the most serious and life-threatening form of tachycardia, a heart rhythm abnormality that causes the heart to beat too quickly. The heart rate can reach up to 250 beats per minute, which is much faster than the normal rate of 60 to 100 beats per minute. During V-Tach, the heart's electrical signals become chaotic and uncoordinated, causing the heart to beat erratically and quickly.

V-Tach can occur suddenly and without warning, although it is more common in people with certain underlying conditions, such as heart disease, high blood pressure, or heart defects. People with V-Tach are at risk of experiencing cardiac arrest, which can lead to death if not treated quickly.

What Can Cause Pulseless Ventricular Tachycardia?

The most common cause of pulseless V-Tach is an electrical disturbance in the heart known as ventricular tachycardia. This arrhythmia occurs when the electrical signals in the heart become rapid and chaotic, causing the heart to beat too quickly and inefficiently. This can be caused by a variety of factors, including coronary artery disease, cardiomyopathy, and certain medications or toxins.

In some cases, V-Tach can be caused by an underlying structural abnormality of the heart, such as a congenital heart defect. Congenital heart defects are present at birth and can cause the heart to beat too quickly, leading to V-Tach. Other structural abnormalities, such as hypertrophic cardiomyopathy, can also cause V-Tach.

Finally, V-Tach can be caused by certain medications, toxins, and other substances. Certain medications, such as beta-blockers, can cause the heart to beat too quickly. Other substances, such as cocaine and other drugs, can also cause V-Tach.


It is important to remember that not all patients will require an AED, and that AEDs are only one part of the overall treatment for cardiac arrest. However, for those patients who do require an AED, it is important to ensure that the AED is properly functioning and that the patient has a shockable rhythm. With the proper use of an AED, many lives can be saved.

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