AFib vs. VFib: What Are the Differences in Symptoms and Treatment?

Atrial fibrillation (AFib) and ventricular fibrillation (VFib) are two heart rhythm problems that sound similar but are very different. AFib is a common heart condition. It affects 1 in 3 white people in the U.S. and 1 out of every 5 Black people in the U.S. during their lifetime. It’s more common in people over the age of 65. But younger people can get AFib as well. 

VFib is what happens when someone has sudden cardiac death. It’s almost always fatal without prompt cardiopulmonary resuscitation (CPR) and a shock to the heart with an automatic external defibrillator (AED) or another type of defibrillator. So, it’s important to understand the differences and the context for both conditions.

What is the difference between the atria and the ventricles?

The heart has four chambers: two atria and two ventricles. Here are the differences:

• The atria are the top two chambers of the heart. They pump blood into the ventricles below them. 

• The ventricles are the two bottom chambers of the heart. The right ventricle pumps blood to the lungs. The left ventricle pumps blood to the rest of the body. The left ventricle is the strongest part of the heart. 

The heart chambers do the pumping. But there’s also an electrical system that runs through the heart, telling it when to pump. This system keeps the heart beating in a normal, organized way.

A normal electrical impulse usually starts at the top of the heart, in the right atrium. From there, the electrical impulse spreads to the left atrium. It then travels down the center of the heart to both ventricles. Most of the time, both ventricles contract at about the same time. 

Both AFib and VFib are types of arrhythmias, a term that means the heart isn’t beating normally. This happens when something is wrong with the electrical system we just described. In AFib, the problem is in the atrium. And in VFib, the problem is in the ventricles.

Causes of AFib vs. VFib

In addition to their differences in how they impact the heart, AFib and VFib are caused by different things.

AFib

AFib happens when the atria fire erratically. Instead of an organized rhythmic squeeze, the atria look like they’re quivering. Only some of these electrical impulses make it to the lower part of the heart. This makes the ventricles beat irregularly, but they usually continue to pump strongly.

AFib is often caused by other health problems, including:

• High blood pressure (hypertension)

• Heart valve disease

• Overactive thyroid disease (hyperthyroidism)

• Lung disease like asthma or chronic obstructive pulmonary disease (COPD)

• Blood clots in the lungs (pulmonary embolism)

• Coronary heart disease

• Congestive heart failure

• A BMI over 30

• Sleep apnea

• Excessive alcohol consumption

• Personal drug use like cocaine and amphetamines

Diabetes is another risk factor, but it may not directly cause AFib. Chronic kidney disease is also a risk factor. AFib can happen to anyone. But it’s more common in people of European ancestry and in those over the age of 65.

Sometimes, AFib happens without an obvious cause. This is called lone atrial fibrillation (LAF). LAF is more common in people under the age of 50. Usually it’s due to abnormal electrical tissue in the heart.

VFib

VFib happens when the ventricles have a very erratic and unorganized rhythm. Multiple electrical impulses fire at the same time in the ventricles. This means that the heart is unable to pump blood to the rest of the body. Without CPR and a shock to the heart with an AED or an automated implantable cardioverter defibrillator (AICD), this rhythm will cause death within minutes.

VFib can be caused by:

• Heart attacks 

• Scar tissue in the heart from a previous heart attack

• Cardiomyopathy (a disease of the heart muscle)

• Some drug and medication overdoses, including illicit drugs and prescription medications

• Electrocution

• A sudden blow to the chest (a rare condition called commotio cordis)

• Abnormally high or low potassium levels

• Some congenital heart problems 

Symptoms of AFib vs. VFib  

AFib usually causes a fast heartbeat. But because of the heart’s electrical system, it’s rare for the heart rate to go over 200 beats per minute (bpm). This means that someone with AFib might feel dizzy, but they probably won’t pass out. Other symptoms of AFib may include:

• Heart palpitations or racing

• Chest tightness, pain, or discomfort

• Shortness of breath

• Fatigue

• Weakness

VFib may have no warning signs. You might feel very dizzy for a few seconds before you pass out. Unlike AFib, someone with VFib will always lose consciousness. This is because the body quickly loses blood flow, including to the brain.

Some people may have another arrhythmia, ventricular tachycardia, which starts before VFib. This rhythm is usually over 100 bpm and starts in the ventricles. It may start and stop on its own and doesn’t always lead to VFib. The symptoms of ventricular tachycardia are very similar to those of AFib.

Treatment of AFib vs. VFib

AFib needs treatment to manage the condition and its symptoms, as well as to lower the risk of stroke. When the atria quiver, blood can pool in small pockets of the heart. This may lead to blood clots. If these clots enter your bloodstream, they may travel to your brain, causing a stroke.

The treatment of AFib focuses on three main things: 

• Blood thinners to reduce your risk for stroke

• Slowing down the heart rate

• Preventing AFib from coming back

Some people live with persistent AFib. If they have few symptoms and are on the right medications, this may not be a problem. But there are both medications and procedures that can help prevent AFib. Often, an electrophysiologist (a cardiologist specializing in heart rhythm problems) can help you manage the problem. 

VFib is treated with an electrical shock to the heart. This is often done by paramedics, or bystanders using an AED. 

For people with an AICD, the device will only fire if it detects VFib. AICDs are usually placed by an electrophysiologist. If you survive an episode of VFib, then you may get an AICD. If you’re at high risk for VFib, your cardiologist may recommend an AICD even if you’ve never had a VFib episode. Sometimes medication can also help prevent additional episodes of VFib.

Can atrial fibrillation turn into ventricular fibrillation, or vice versa?

Most people with AFib will not get VFib. But they do have a higher risk compared to the general population. And people with certain inherited conditions, like Wolff-Parkinson-White syndrome, are more likely to get VFib if they also have AFib.

VFib will almost never turn into AFib. Sometimes, when the heart is shocked out of VFib, it’ll go into AFib. But if VFib isn’t treated, it’s almost always fatal.

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Written by:

Sarah A. Samaan, MD

Sarah Samaan, MD, FACC, FACP, FASE is a board-certified cardiologist who practiced clinical cardiology for nearly 30 years. She is a member of the American College of Cardiology, the American College of Physicians, and the American Society of Echocardiography.

Edited by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

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