What Is Atrioventricular (AV) Block?

Your heart runs on electricity. A steady signal travels from your upper right chamber (atrium) to your lower chambers (ventricles). But sometimes this current gets delayed or stopped. The result: a condition called atrioventricular (AV) block or heart block.

Certain health conditions, heart defects, and medicines can cause it. You might not have symptoms or need treatment. But if you do, a doctor can help you manage your condition. Without the right care, serious AV block can be life threatening.

How AV Block Happens

Your heart has four chambers that work together. They team up to pump blood through your body.

An electrical signal starts out in a spot called the sinoatrial (SA) node. It's known as your heart's natural pacemaker.

The current heads down to a group of cells called the atrioventricular (AV) node. This "relay station" slows the current down before it goes to your ventricles. Then your heart squeezes, or contracts. When you're at rest, this usually happens about 60-100 times each minute.

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When you have heart block, the electrical signal from your heart's upper chamber slows down or gets interrupted on its way to the lower chambers.

You can get mild AV block as your heart adapts to an intensive exercise routine. It's sometimes called "athlete's heart." But AV block is more likely to happen if you're older or there's something wrong with your heart.

Causes

The most common causes of AV block include:

Fibrosis or sclerosis. Extra tissue can thicken, scar, and damage the pathways that send signals from the upper part to the lower part of your heart.

Coronary artery disease. This damages your heart's blood vessels. It may cause AV block before or after a heart attack.

Some other causes are:

Medication. Certain drugs can slow your heartbeat. This includes blood pressure medicine like beta-blockers and calcium channel blockers.

Increased vagal tone. This happens when you have more activity in a nerve called the vagus nerve. It's a problem that sometimes shows up if you're very physically fit.

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Birth defect or genetic disorder. You may inherit certain heart conditions that lead to heart block.

Illnesses. Some diseases and infections can hurt your heart, like rheumatic fever, sarcoidosis, lupus, and Lyme disease.

Electrolyte imbalance. Your heart may not beat normally if you don't have the right amount of minerals in your blood. AV block may happen if you have too much potassium.

Heart surgery. Your electrical system may get damaged during the process.

Types of AV Block

There are three different levels of AV block, including:

First-degree. You'll have a delay in electrical signals. Your heartbeat won't get blocked, but it may slow down. This kind is more common in athletes and young people.

Second-degree (Mobitz type 1 or 2). Some electrical signals won't make it through. You'll have "dropped" beats. Your heart rhythm may be slow, irregular, or both.

Third-degree. No electrical pulses will get through, which is why it's sometimes called complete heart block. Other parts of your heart, like your AV node or ventricles, will have to create their own current. But these signals are less reliable. Your heart may only beat 30-50 beats per minute.

Symptoms

How AV block affects you depends on the kind of heart block you have. With first-degree, you may not notice anything.

With second-degree, you may:

With third-degree, you may get more serious symptoms, like:

How Is It Diagnosed?

The first thing your doctor will do is give you a physical exam and ask about your medical history. Don't forget to tell them about any medicines you're taking or if heart problems run in your family. They may send you to a heart specialist called a cardiologist.

They'll also check your heart with an electrocardiogram. You may hear this called an ECG or EKG. It puts the rate, rhythm, and electrical timing of your heart on a graph. And each type of AV block has its own electrical pattern.

For more detailed results, your doctor may recommend:

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Holter or event monitor. These are portable ECGs that can check your heart's signals for a longer period of time. You'll wear a Holter for a day or two or an event monitor for a month or so.

Implantable loop recorder. You can wear this for up to 2 years. Your doctor may give you one if your symptoms don't happen often.

Electrophysiology study. A surgeon puts a thin, bendable wire (catheter) on top of your heart. They'll do this at the hospital.

What Are Your Treatment Options?

You may not need to do anything if you have first-degree AV block. But if your condition is more serious, a doctor may give you an artificial pacemaker. That's a device that sends an electrical current to keep your heart pumping.

Your doctor will put the pacemaker under your skin. They'll most likely place it under your left or right collarbone. It'll connect to your heart with wires that run through your veins.

Your doctor may also need to treat the condition that is causing your heart block. You may need to change your medicine or manage your heart disease.

WebMD Medical Reference Reviewed by Carmelita Swiner, MD on February 19, 2020

Sources

SOURCES:

Cleveland Clinic: "Heart Block."

Johns Hopkins: "Heart Block."

Merck Manuals: "Atrioventricular Block." 

National Heart, Lung, and Blood Institute: "Conduction Disorders."

European Society of Cardiology: "Electrocardiographic findings in athletes."

Journal of Tehran University Heart Center: "Heart and Athlete."

The Journal of Physiology: "CrossTalk Proposal: Bradycardia in the trained athlete is attributable to high vagal tone."

American Heart Association: "Conduction Disorders."

Kardiologia Polska: "Complete atrioventricular block after isolated aortic valve replacement."

Heart and Stroke Foundation of Canada: "Heart Block."

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