Bradycardia

Types

Bradycardia has two main causes: sinus node dysfunction and AV node dysfunction.

Sinus Node Dysfunction

A sinus node malfunction is often called sick sinus syndrome. The heart's sinus node, the "spark plug" that distributes the electrical signal throughout the heart muscle, does not work properly. This can cause rhythm problems if the signals through the sinus node are blocked, the sinus node is paused or stopped, or the signals alternate fast and slow. Sick sinus syndrome is common in older people. It sometimes alternates with episodic atrial fibrillation, a condition in which the heart beats too fast.

AV Node Dysfunction

The atrioventricular (AV) node connects the sinus node electrically to the ventricles (the main pumping chambers in the heart). When the conduction system through the AV node is disrupted, bradycardia or other heart rhythm disorders can occur. AV node dysfunction (sometimes called heart block) can be caused by medications, other medical conditions, or in combination with other cardiovascular conditions. AV node dysfunction can have various degrees of severity, depending on how many electrical signals are passing through the AV node.