Conduction Disorders - Types - Types
\nThere 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.
\nRead about other types of conduction disorders not covered in this topic, including atrial fibrillation and arrhythmia.
\nLearn more about the cardiac conduction system in our How the Heart Works Health Topic.
\n![\"Illustration](\"https://www.nhlbi.nih.gov/sites/default/files/inline-images/conduction-disorders-1.jpg\")
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\n \n Sick sinus syndrome \n - Conduction Disorders - Types
\n 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:
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- The heart rate cannot be increased when needed, such as with exercise or stress. \n
- The signal is not conducted from the SA node. \n
- There are pauses or stops during the generation of the electrical signal in the SA node. \n
- There is a slow or fast heart rate. \n
\n \n Atrioventricular block \n - Conduction Disorders - Types
\n There are three main types of AV block, depending on how severe the conduction disorder is: first-, second-, and third-degree AV block.
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- 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. \n
- Second-degree AV block occurs when some electrical signals from the atria do not reach the ventricle , leading to dropped beats. More severe cases of second-degree AV block can turn into third-degree AV block. \n
- 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. \n
\n \n Bundle branch blocks \n - Conduction Disorders - Types
\n 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.
\n \n \n Ion channel disorders \n - Conduction Disorders - Types
\n 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\u2019s 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\u2019s electrical activity.
\nThe most common type of ion channel disorder is long QT syndrome. Other types include Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, and short QT syndrome.
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