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.
Learn more about the cardiac conduction system in our How the Heart Works Health Topic.
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:
There are three main types of AV block, depending on how severe the conduction disorder is: first-, second-, and third-degree AV block.
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.
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.
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.
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.
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.
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:
Some medical conditions may increase your risk for a conduction disorder, including the following.
Some medicines may increase your risk for developing a conduction disorder, including the following.
Brugada syndrome is especially common in people of Asian descent, particularly those of Japanese, Filipino, and Thai ancestry.
The following conduction disorders are more common in men than in women:
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.
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 Diagnosis section.
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.
While many conduction disorders cannot be prevented, your doctor may recommend the following steps to lower your chances of developing a conduction disorder.
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.
You may experience the following signs or symptoms if you have a conduction disorder:
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.
Your doctor may ask questions about your personal medical history using questions such as the following:
Your doctor may ask about your family’s medical history, including:
As part of your physical exam, your doctor may listen to your heart, record your heart rate, and measure your blood pressure.
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:
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.
Different conduction disorders have different triggers. Depending on your disorder, your doctor may ask you to do one or more of the following.
Your doctor may recommend one or more of the following types of medicines to treat your conduction disorder:
Your doctor may recommend one of the following procedures to treat a conduction disorder or implant a medical device.
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.
Unless caused by a medicine or blood electrolyte imbalance, conduction disorders are often lifelong conditions for which you will need to continue receiving care.
Return to Treatment to review possible treatment options for your conduction disorder.
Your doctor may recommend the following to monitor your condition:
To help prevent complications such as dangerous arrhythmias, your doctor may recommend the following.
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.
If you have a conduction disorder, your doctor may recommend medicines or procedures to help prevent or stop an arrhythmia. These include the following.
Learn about the following ways the NHLBI continues to translate current research into improved health for people who have conduction disorders. Research on this topic is part of the NHLBI’s broader commitment to advancing heart and vascular disease scientific discovery.
In support of our mission, we are committed to advancing conduction disorder research, in part through the following ways.
Learn about exciting research areas the NHLBI is exploring about heart conduction disorders.
We lead or sponsor many studies on conduction disorders. See if you or someone you know is eligible to participate in our clinical trials.
After reading our Conduction Disorders Health Topic, you may be interested in additional information found in the following resources.