Arrhythmias Conduction Disorders

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A conduction disorder, also known as heart block, is a problem with the electrical system that controls your heart’s rate and rhythm. This system is called the cardiac conduction system.

Normally, the electrical signal that makes your heart beat travels from the top of your heart to the bottom. The signal causes your heart muscle to beat and pump blood to your lungs and the rest of your body. In conduction disorders, this electrical signal either does not get produced properly, does not travel the way it should through the heart, or both.

The image above shows how cardiac conduction works. The signal starts with cells in the sinoatrial (SA) node that cause the heart to beat. These are called pacemaker cells. The signal causes your right and left atria to contract. The signal then travels down to your atrioventricular (AV) node and bundle branches, causing your right and left ventricles to contract.

There are many types of conduction disorders that can happen anywhere along the cardiac conduction system: at the SA node, the AV node, or the bundle branches.

• Sick sinus syndrome (SSS), also known as sinus node disease: The SA node controls the rate and rhythm of your heartbeat. SSS can cause a slow or fast heart rate. It can also cause problems with increasing your heart rate when needed, such as when you exercise.
• Atrioventricular (AV) block: There are three degrees of AV block, depending on how serious your condition is. The third degree is called complete heart block. This happens when no signals reach your ventricles, the lower chambers of the heart. This can cause serious symptoms such as a very slow heart rate, fainting, and chest pain.
• Bundle branch blocks: These happen when the electrical signals travel more slowly in one side of your heart than in the other. This causes your ventricles to contract at different times than normal. You may have a left bundle branch block or a right bundle branch block, depending on which side is delayed.
• Ion channel disorders: On the surface of each heart muscle cell are tiny pores called ion channels. These channels help produce your heart’s electrical activity. The most common type of ion channel disorder is long QT syndrome. Other types include Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, and short QT syndrome.

Learn more about the cardiac conduction system in our How the Heart Works topic.

Many people who have conduction disorders may not have any symptoms. Others may have symptoms of arrhythmias that happen in specific situations, such as when you experience physical or emotional stress or when you sleep. Your symptoms may include:

• Slow or fast heart rate
• Heart palpitations
• Dizziness or lightheadedness
• Extreme tiredness
• Fainting
• Shortness of breath
• Chest pain or discomfort
• Gasping or trouble breathing during sleep

If you or your child has any risk factors, your doctor may order heart tests and genetic testing to screen you for conduction disorders. You may also need screening tests if you play competitive sports or if you need to have surgery.

To diagnose a conduction disorder, your doctor will ask about your medical history, your family’s medical history, and your symptoms. They will perform a physical exam and may order blood tests, genetic testing, and heart tests such as an electrocardiogram, or EKG or a stress test.

Some people have a conduction disorder at birth, while others develop it later in life.

Age

Conduction disorders can happen at any age, but some are more common at certain ages. For example, sick sinus syndrome and bundle branch blocks are more common in older adults because of normal changes to the conduction system as you age.

Family history and genetics

Some disorders are more common among families.

• Brugada syndrome is an irregular heartbeat in the lower chambers of the heart. This condition is more common in people of Asian descent, particularly those of Japanese, Filipino, and Thai ancestry.
• Complete heart block or third-degree AV block is more common in children born to mothers who have a connective tissue disorder.
• Wolff-Parkinson-White syndrome is more common in people whose family members also have this condition.

Other medical conditions

• Autoimmune diseases
• Heart and blood vessel diseases
• High or low electrolyte levels
• Muscular dystrophy
• Problems with your thyroid hormone levels
• Sleep apnea

Medicines

Some medicines to treat high blood pressure, arrhythmias and other heart conditions, and depression and other mental illnesses can raise your risk.

Sex

Brugada syndrome and catecholaminergic polymorphic ventricular tachycardia are more common in men than in women.

The following steps may help prevent some types of conduction disorders or lower your risk of complications.

• Adopt a heart-healthy lifestyle. 
• Work with your doctor to avoid medicines that raise your risk of conduction disorders.
• Limit alcohol and avoid illegal drug use.
• Manage medical conditions that raise your risk of conduction disorders.

Your treatment will depend on the type of conduction disorder you have and how serious it is. If you have very mild or no symptoms, you may not need any treatment.

Your treatment may include one or more of the following:

• Medicines to make your heart beat faster or slower, depending on the problem with your heart
• Surgery or implantable devices such as defibrillators or pacemakers
• Vagal maneuvers, which are techniques to slow down your heart rate

Conduction disorders are often lifelong conditions that require continued care. Complications of conduction disorders may be serious or life-threatening, and they include:

• Arrhythmias
• Cardiac arrest
• Heart failure
• Stroke caused by atrial fibrillation

Call 9-1-1 right away if someone has symptoms of a stroke or sudden cardiac arrest. Look for an automated external defibrillator (AED) nearby and follow the instructions to help restart the heart after sudden cardiac arrest.

Visit the Living With Arrhythmias page to learn how to prevent these complications.