Atrioventricular heart block

Overview

Atrioventricular (AV) block is a change in the electrical signals that tell the heart when to beat. These signals usually move from the heart's upper chambers, called the atria, to the lower chambers, called the ventricles. With AV block, the signals slow down or do not get through.

A type of atrioventricular block called first-degree AV block is common. It's mostly seen in adults. First-degree AV block may not cause symptoms. Some people may not need treatment. Other types of AV block can slow the heartbeat enough to reduce blood flow. People with these types may need urgent treatment or pacemakers.

AV block is different from bundle branch block. Bundle branch block affects electrical signals in the heart's lower chambers. AV block affects signals that travel from the heart's upper chambers to its lower chambers.

AV block can happen at birth or develop within the first three months after birth. This is called congenital AV block.

Types

There are three main types of atrioventricular (AV) block. They are named based on how electrical signals travel from the upper heart chambers, called the atria, to the lower heart chambers, called the ventricles. Conduction is the medical term for the way electrical signals move through the heart.

First-degree AV block

Every electrical signal from the upper heart chambers reaches the lower ones. But signaling takes longer than usual. A slow heartbeat, called bradycardia, can occur at the same time as first-degree AV block.

Second-degree AV block

Some electrical signals from the upper heart chambers do not reach the lower ones. Second-degree AV block can occur in different patterns:

• Mobitz type 1, also called Wenckebach. The way the heart signals move gets slower over time. Eventually, a signal from the upper heart chambers doesn't get to the lower heart chambers.
• Mobitz type 2. A signal from the upper heart chambers may suddenly fail to get to the lower heart chambers. This happens without the slowing seen with type 1. If every other signal from the upper heart chambers reaches the lower ones, it's called a 2:1 pattern or 2:1 AV block. If two or more signals in a row don't reach the lower chambers, it's called advanced, high-grade or high-degree AV block.

Third-degree AV block

Third-degree AV block also is called complete heart block. In this type, electrical signals from the heart's upper chambers do not reach the lower chambers. Because of this, the upper and lower chambers beat on their own instead of working together.

The lack of heart signaling in third-degree AV block can cause a very slow heartbeat or poor blood flow. It needs treatment right away.

Symptoms

Symptoms of atrioventricular (AV) heart block depend on the type of AV block and how well the lower heart chambers work. Symptoms also depend on how often the block in heart signaling happens.

Symptoms may include:

• Feeling very tired, called fatigue.
• Feeling dizzy or lightheaded, including during exercise.
• Fainting or feeling like you may faint.

Some people with AV block have no symptoms.

When to seek care

Make an appointment with a healthcare professional if you feel dizzy, lightheaded or like you may faint. Also make an appointment if you are more tired than usual or can't exercise as you usually do. These symptoms may occur when AV block slows the heart enough to reduce blood flow.

When to seek emergency care

Atrioventricular (AV) block can cause a slow heartbeat that lessens blood flow. Call 911 or your local emergency number if you have:

• Chest pain.
• Low blood pressure.
• Confusion.
• Dizziness or lightheadedness.
• Fainting.

Causes

Atrioventricular (AV) heart block can have many causes, including:

• Reduced blood flow to the heart, such as from a heart attack.
• Heart disease or damage that affects the signals that control the heartbeat.
• Infections, such as Lyme disease, that can affect the heart.
• Some thyroid conditions. These include not enough thyroid hormone, called hypothyroidism, or too much thyroid hormone, called hyperthyroidism.
• Some conditions that affect electrolytes, such as a high potassium level, called hyperkalemia.
• Inflammatory disease, such as sarcoidosis or rheumatoid arthritis.
• Increased activity from the vagus nerve, which controls the heartbeat.
• Medicines that can slow heart rate or heart signaling. These medicines include beta blockers, some calcium channel blockers, digoxin and some medicines used to treat irregular heartbeats. AV block linked to the medicine may continue or return even after the medicine is changed or stopped.

Risk factors

Some things may make you more likely to have some types of atrioventricular (AV) heart block. Risk factors may include:

• Older age.
• Male sex.
• Obesity or being overweight.
• Diabetes.
• Chronic kidney disease.
• Some heart signaling changes seen on a heart test called an electrocardiogram (ECG or EKG).

Having one or more of these risk factors does not mean that you will develop AV block.

Complications

Complications of atrioventricular (AV) heart block can happen when the lower heart chambers beat too slowly to pump enough blood throughout the body.

Your risk of complications may depend on:

• The type of AV block.
• How fast the lower heart chambers work.
• How often the AV block happens.
• Whether you have heart disease.

Possible complications of AV block include:

• Fainting.
• Very low blood pressure or shock. A heartbeat that is too slow makes it hard for the heart to pump enough blood to meet your body's needs.
• Acute heart failure. A very slow heartbeat can reduce your heart's ability to pump effectively.