A conduction disorder is a problem with the electrical system that makes your heart beat and controls its 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 triggers your heart muscle, causing your heart to beat and pump blood to your lungs and body. In conduction disorders, this electrical signal either does not generate properly, or it does not travel properly through the heart, or both.

The types of conduction disorders, such as atrioventricular (AV) blocks and bundle branch blocks, vary depending on where they occur in the conduction system. Certain medicines can cause conduction disorders, as can conditions such as ischemic heart disease or heart attack, or your genetics. Your doctor may be able to diagnose a conduction disorder with an electrocardiogram (EKG), which is a reading of your heart’s electrical activity.

Conduction disorders may be treated with medicines, pacemakers, implantable cardioverter defibrillators (ICDs), and surgical procedures. Treatment depends on the location, type, and severity of your conduction disorder. Your doctor will consider how the disorder affects your heart and symptoms, which can differ from one person to the next. Sometimes an irregular heartbeat, called an arrhythmia, is the first sign of a conduction disorder. If left untreated, severe conduction disorders can lead to sudden cardiac arrest, in which the heart suddenly stops beating.

Your heartbeat is the contraction of your heart to pump blood to your lungs and the rest of your body. Your heart's electrical system determines how fast your heart beats.

Your heartbeat

The contraction of the atria and ventricles makes a heartbeat. When your heart beats, it makes a “lub-DUB” sound. You may have heard this if you listened with a stethoscope or with your ear on someone's chest.

• After your atria pump blood into the ventricles, the valves between the atria and ventricles close to prevent backflow. The “lub” is the sound of these valves closing.
• After your ventricles contract to pump blood away from the heart, the aortic and pulmonary valves close and make the “DUB” sound.

What is my pulse, and how do I measure it?

Your pulse is the rate your heart beats. It is also called your heart rate. To find your pulse, gently place your index and middle fingers on the artery located on the inner wrist of either arm, below your thumb. You should feel a pulsing or tapping against your fingers.

Watch the second hand or set the timer on your stopwatch or phone, and count the number of beats you feel in 30 seconds. Double that number to find out your heart rate or pulse for one minute.

• At rest, your heart typically beats about 60 to 70 times per minute.
• When you exercise, your heart beats faster, and your heart rate speeds up to get more oxygen to your muscles.

Electrical activity

Electrical signals cause muscles to contract. Your heart has a special electrical system called the cardiac conduction system. This system controls the rate and rhythm of the heartbeat.

With each heartbeat, an electrical signal travels from the top of the heart to the bottom. As the signal travels, it causes the heart to contract and pump blood. The heartbeat process includes the following steps.

• The signal begins in a group of cells, called pacemaker cells, located in the sinoatrial (SA) node in the right atrium.
• The electrical signal travels through the atria, causing them to pump blood into the ventricles.
• The electrical signal then moves down to a group of pacemaker cells called the atrioventricular (AV) node, located between the atria and the ventricles. Here the signal slows down slightly, allowing the ventricles time to finish filling with blood.
• The AV node fires another signal that travels along the walls of your ventricles, causing them to contract and pump blood out of your heart.
• The ventricles relax, and the heartbeat process starts all over again in the SA node.

Some conditions affect the heart's electrical system. Examples include:

• Arrhythmia, or an irregular heart rhythm. Atrial fibrillation is one of the most common types of arrhythmia.
• Conduction disorders, in which electrical signals either do not generate properly, or they do not travel properly through the heart, or both.

There are many types of conduction disorders that can occur anywhere along the cardiac conduction system: at the sinoatrial (SA) node, the atrioventricular (AV) node, or the bundle branches. The problem can be with signal generation, how the signal travels through the heart, or both. Disorders can occur on a much smaller level within ion channels in a heart muscle cell that work together to make the heart cell contract.

Sick sinus syndrome

Sick sinus syndrome (SSS), also known as sinus node disease, describes problems that can occur when the SA node does not work properly. The SA node controls the rate and rhythm of your heartbeat. SSS includes conditions in which the following occurs:

• The heart rate cannot be increased when needed, such as with exercise or stress.
• The signal is not conducted from the SA node.
• There are pauses or stops during the generation of the electrical signal in the SA node.
• There is a slow or fast heart rate.

Atrioventricular block

There are three main types of AV block, depending on how severe the conduction disorder is: first-, second-, and third-degree AV block.

• First-degree AV block occurs when the electrical signal for your heartbeat moves too slowly. This may lead to a slower heart rate, but no heartbeats are blocked.
• Second-degree AV block occurs when some electrical signals from the atria do not reach the ventricles, leading to dropped beats. More severe cases of second-degree AV block can turn into third-degree AV block.
• Third-degree AV block, also called complete heart block, occurs when no signals reach the ventricles, resulting in serious symptoms such as a very slow heart rate, fainting, and chest pain. This may be discovered at birth, or it may be due to other heart conditions, drugs, or injury to the heart during heart surgery. Children who have congenital complete heart block often have mothers who have an autoimmune disease such as lupus.

Bundle branch blocks

Usually, the electrical signal in the heart travels down the left and right bundle branches at the same speed, causing the ventricles to contract or squeeze at the same time. Sometimes one side travels more slowly than the other, causing that ventricle to contract slightly after the other ventricle. This is known as a bundle branch block and is called a left bundle branch block (LBBB) or a right bundle branch block (RBBB), depending on which side the block occurs. Bundle branch blocks may also be more or less severe.

Ion channel disorders

On the surface of each heart muscle cell are tiny pores called ion channels. Ion channels open and close to let electrically charged sodium, calcium, and potassium ions flow into and out of each cell. This generates the heart’s electrical activity, which triggers the contracting and relaxing of the ventricles to pump blood and refill. Ion channels that do not work properly may cause problems with the 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.

Conduction disorders may be caused by structural problems in the heart or other medical conditions. Some people have a conduction disorder at birth, while others develop it later in life.

Structural problems in the heart

A congenital heart defect—one that is present at birth—can cause structural damage even when the heart appears normal. This can prevent the cardiac conduction system from working properly. For example, the conduction system may be damaged during fetal development. This is seen in people who have a genetic condition called Holt-Oram syndrome, who have different degrees of cardiac conduction system problems such as AV block.

Other medical conditions

Other conditions that cause conduction disorders include the following:

• Electrolyte problems such as high or low blood levels of potassium, calcium, and magnesium
• Fever in Brugada syndrome
• Heart attack

You may have an increased risk for conduction disorders because of your age, family history and genetics, medical conditions, medicines, race or ethnicity, or sex. These factors can differ by the type of conduction disorder you have.

Age

Conduction disorders can happen at any age, but some are more common at certain ages. For example, SSS and bundle branch blocks are more common in older adults due to fibrosis and changes in the conduction system that happen as a result of aging.

Family history and genetics

Your family history can increase your risk for a conduction disorder. Even when it is not known exactly how a conduction disorder is inherited, some disorders are more common among families, including:

• Brugada syndrome
• Complete heart block or third-degree AV block, in children born to mothers who have a connective tissue disease
• Wolff-Parkinson-Whitesyndrome

Other medical conditions

Some medical conditions may increase your risk for a conduction disorder, including the following.

• Autoimmune diseases, such as scleroderma, systemic lupus erythematosus, and rheumatoid arthritis
• Cardiomyopathy
• Complications of a heart surgery or procedure, including heart valve replacement, procedures to treat ischemic heart disease, surgery to correct a congenital heart defect at birth, and radiation treatment for cancer. The damage to the conduction system may be caused by physical damage during the surgery or procedure, or from damage due to swelling, lack of blood flow, or hematoma.
• Diseases in which there are deposits of abnormal substancesin the heart, such as amyloidosis, hemochromatosis, and sarcoidosis
• Endocrine conditions, such as hypothyroidism
• Heart inflammation, such as in myocarditis and pericarditis
• High blood pressure
• Neuromuscular disorders such as muscular dystrophy
• Sleep apnea

Medicines

Some medicines may increase your risk for developing a conduction disorder, including the following.

• Antiarrhythmics to treat abnormal heart rhythms, such as quinidine, flecainide, sotalol, and amiodarone
• Antidepressants and antipsychotic medicines
• Diuretics, which are medicines that remove excess water from your body
• Heart medicines, such as beta blockers, calcium channel blockers, and digoxin
• High blood pressure medicines, including clonidine and methyldopa
• Lithium
• Muscle relaxants and sedatives

Race or ethnicity

Brugada syndrome is especially common in people of Asian descent, particularly those of Japanese, Filipino, and Thai ancestry.

Sex

The following conduction disorders are more common in men than in women:

• Brugada syndrome
• Catecholaminergic polymorphic ventricular tachycardia

If you or your child has known risk factors for a conduction disorder, the doctor may recommend screening, which may include genetic testing. Screening tests for conduction disorders may also be suggested for competitive athletes. Depending on the cause of your conduction disorder, heart-healthy lifestyle changes and other precautions may help decrease the risk of developing a conduction disorder.

Screening tests

High school and college athletes may be screened by their own physician. The doctor will ask about personal history and family history, in addition to performing a physical exam. EKGs or echocardiograms are used by many colleges to screen athletes—either all athletes or those who are at high risk. Learn more about EKGs and echocardiograms in the Diagnosissection.

When one family member has an inherited conduction disorder, close relatives may need a physical exam and medical tests, including genetic testing. This screening may help find conduction disorders early and lead to prompt treatment or monitoring.

If you are scheduled for surgery or a procedure, your doctor may recommend an EKG to screen for any heart problems including conduction disorders. Heart monitoring can also help detect problems that may emerge after the procedure.

Prevention strategies

While many conduction disorders cannot be prevented, your doctor may recommend the following steps to lower your chances of developing a conduction disorder.

• Following a heart-healthy lifestyle to lower the chance of ischemic heart disease, limiting alcohol, and avoiding illegal drug use.
• Managing conditions and medicines that change the normal levels of potassium, calcium, and magnesium.
• Taking an angiotensin converting enzyme (ACE) inhibitor, used to treat high blood pressure. This may lower the risk of developing a conduction disorder in people who have high blood pressure.

Many people who have conduction disorders, such as first-degree AV block, may have no obvious signs or symptoms. Others may have signs and symptoms that occur in specific situations, such as when you experience physical or emotional stress or when you sleep. Conduction disorders can lead to life-threatening arrhythmias if undiagnosed or untreated.

Signs and symptoms

You may experience the following signs or symptoms if you have a conduction disorder:

• Fatigue
• Dizziness or lightheadedness
• Slow or fast heart rate
• Shortness of breath
• Heart palpitations
• Chest pain or discomfort
• Abdominal pain
• Nausea
• Fainting or loss of consciousness
• Gasping or labored breathing during sleep
• Seizures

Complications

Complications of conduction disorders may be serious or life-threatening, and they include the following:

• Arrhythmia,or irregular heart rhythm, which may be life-threatening
• Heart failure
• Stroke caused by atrial fibrillation in SSS
• Sudden cardiac arrest

To diagnose a conduction disorder, your doctor will ask about your medical history, any signs and symptoms, and your family’s medical history, and he or she will perform a physical exam. Your doctor may also recommend tests to look at your heart’s electrical activity and structure and to determine if you have genetic changes that may signal a conduction disorder.

Medical history

Your doctor may ask questions about your personal medical history using questions such as the following:

• Do you experience heart palpitations?
• Do you experience unusual shortness of breath or fatigue with exercise?
• Do you have high blood pressure?
• Do you have symptoms of sleep apnea?
• Have you ever fainted or almost fainted without a known reason?
• Have you experienced chest pain or discomfort with exertion or exercise?
• What medicines are you taking?

Your doctor may ask about your family’s medical history, including:

• Complications from heart disease in a close relative
• Premature death of a relative, either sudden or unexpected
• Specific knowledge of heart conditions in family members

Physical exam

As part of your physical exam, your doctor may listen to your heart, record your heart rate, and measure your blood pressure.

Diagnostic tests and procedures

To diagnose a conduction disorder, your doctor may order an EKG, which records your heart’s electrical activity. Each conduction disorder has a specific pattern that can be seen on an EKG.

If the diagnosis is unclear from the EKG or your doctor would like more information, your doctor may order additional tests, such as one or more of the following:

• Blood tests to look for potentially reversible causes, including high or low blood electrolyte levels or endocrine disorders such as hypothyroidism, or to check medicine levels.
• Holter or event monitor to record your heart’s electrical activity over long periods of time while you do your normal activities.
• Implantable loop recorder to look at the heart’s electrical activity over a longer period of time or to find a diagnosis if earlier tests do not rule out a conduction disorder. The recorder can transmit data to the doctor’s office to help with monitoring. An implantable loop recorder helps doctors figure out why a person may be having palpitations or fainting spells, especially if these symptoms do not happen very often.
• Stress test to look at changes in your heart’s activity that occur with an increase in heart rate and during recovery after exercise.
• Cardiac magnetic resonance imaging (MRI) or other types of imaging to look at the heart’s structure.
• Echocardiography to look at the heart’s structure and how well it is working.
• Electrophysiology study (EPS) to look at the electrical activity of the heart and to find the source of an abnormal heartbeat. The study uses a wire to stimulate your heart electrically. The information from an EPS may help guide treatment.
• Genetic testing to confirm a genetic diagnosis, as in some ion channel disorders. If you have certain genes known to be risk factors for a conduction disorder, your doctor may also recommend testing other family members.

If a conduction disorder is diagnosed while you are asleep, your doctor may also request a test to find out if you have sleep apnea, which is a common complication.

If you are diagnosed with a conduction disorder, your doctor may recommend lifestyle changes, medicines, surgery, or another procedure to treat your condition. Conduction disorders can be a medical emergency that requires immediate treatment in a hospital emergency department.

Healthy lifestyle changes

Different conduction disorders have different triggers. Depending on your disorder, your doctor may ask you to do one or more of the following.

• Avoid medicines that may trigger your conduction disorder or make it worse.
• Limit exposure to sudden noises, such as in your occupation.
• Limit physical activity or use precautions if exercise puts you at higher risk of dangerous heart rhythms. For example, swimming may be risky for people who have catecholaminergic polymorphic ventricular tachycardia.
• Make heart-healthy lifestyle changes, including heart-healthy eating, managing stress, and limiting alcohol.

Medicines

Your doctor may recommend one or more of the following types of medicines to treat your conduction disorder:

• Atropine to increase heart rate in severe types of AV block.
• Beta blockers to decrease the activity of the stress hormones and make your heart beat more slowly. Examples of beta blockers include nadolol, propranolol, and metoprolol.
• Other medicines, such as antiarrhythmics, may be used to treat certain types of arrhythmias.

Surgery and other procedures

Your doctor may recommend one of the following procedures to treat a conduction disorder or implant a medical device.

• Pacemakers to help your heart beat at a normal rate. Several conduction disorders, including SSS and more severe types of AV block, are treated with a pacemaker. Pacemakers may prevent fainting and improve survival. With research, new, more effective pacemaker technologies are emerging. Complications from pacemakers may include infection, bleeding, and damage to the heart or heart valves.
• Radiofrequency catheter ablation to help prevent abnormal electrical activity. This type of catheter ablation uses radiofrequency energy to destroy a small section of heart tissue that is causing the abnormal electrical activity or arrhythmia.
• Other procedures, such as placing an ICD—a type of defibrillator—or wearing away or removing nerves that are overstimulating the heart, called left cardiac sympathetic denervation, may be used to treat arrhythmias.

If you have been diagnosed with a conduction disorder, it is important that you continue your treatment. Follow-up care may depend on your type of conduction disorder, your risk of a complication, and your response to treatment. If you have a conduction disorder whose cause is genetic, talk to your doctor and family members about possible genetic testing for your family members.

Receive routine follow-up care

Unless caused by a medicine or blood electrolyte imbalance, conduction disorders are often lifelong conditions for which you will need to continue receiving care.

• Continue to take all medicines prescribed for your condition to help prevent symptoms and complications.
• Continue with any precautions that your doctor has advised.
• Keep any appointmentsand tests recommended by your doctor.
• Tell your doctor if you have any symptoms.

Monitor your condition

Your doctor may recommend the following to monitor your condition:

• Blood tests. If the cause of your conduction disorder is due to abnormal electrolyte blood levels or a metabolic disorder, your doctor may request follow-up blood tests.
• Follow-up EKGs to monitor your conduction disorder and to check for any new complications. Having one conduction disorder may put you at higher risk for having another conduction disorder. For example, AV block is more likely in people who have bundle branch blocks.
• Regular check-ups to monitor the data collected by your pacemaker or ICD. If your ICD delivers a shock to restore your heart’s normal rhythm, contact your doctor right away.

Learn about other precautions to help you stay safe

To help prevent complications such as dangerous arrhythmias, your doctor may recommend the following.

• Avoid alcohol if it may trigger an event.
• Avoid any known triggers for your conduction disorder, including emotional or stressful situations.
• Avoid competitive sports and contact sports, if advised by your doctor.
• Avoid medicines or illegal drugs that can make your conduction disorder worse. Ask your doctor about specific medicines you take or plan to take.
• Follow any instructions regarding exercise. Some people are specifically advised not to swim.
• Make recommended changes in what you eat. Your doctor may recommend watching how much potassium you eat.

Learn the warning signs of serious complications and have a plan

Even with treatment for a conduction disorder, a repeat event or arrhythmia may occur. Know the signs and symptoms of your conduction disorder and how to recognize other complications, such as sudden cardiac arrest.

Usually, the first sign of sudden cardiac arrest is fainting. At the same time, no heartbeat can be felt. Some people may have a racing heartbeat or feel dizzy or light-headed just before they faint. Within an hour before cardiac arrest, some people have chest pain, shortness of breath, nausea, or vomiting. Call 9-1-1 right away if someone has signs or symptoms of sudden cardiac arrest. Look for an automated external defibrillator (AED) nearby and follow the instructions.

Prevent complications over your lifetime

If you have a conduction disorder, your doctor may recommend medicines or procedures to help prevent or stop an arrhythmia. These include the following.

• Antiarrhythmics to help prevent an arrhythmia. This class of medicines includes quinidine to treat Brugada syndrome.
• ICD placement to stop an arrhythmia and help prevent sudden cardiac arrest. Survivors of sudden cardiac arrest caused by ventricular fibrillation are at high risk of another arrhythmia. Your doctor may recommend an ICD on its own or with medicines.
• Isoproterenol medicine to suppress a life-threatening arrhythmia.
• Left cardiac sympathetic denervation procedure to reduce the chance of arrhythmia in high-risk patients and those who do not respond to or cannot take certain medicines. This procedure can reduce the release of hormones that stimulate the heart and also make it harder for the heart’s ventricles to produce a dangerous arrhythmia. It reduces the risk of fainting and cardiac arrest.