What is atrioventricular block?

Andrea C. Bryan, MD
Cardiology (Cardiovascular Disease)
Atrioventricular block involves impairment of electrical conduction between the atria and ventricles, or top and bottom chambers of the heart. Normally, a heart beat starts in the top chamber of the heart and travels through the AV node to the ventricles, or main pumping chambers of the heart. With AV block, heart beat conduction is impaired and the ventricles must try to maintain their own pacing mechanism, at a much lower heart rate.

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Atrioventricular (AV) block is a type of abnormal heart rhythm, or arrhythmia. The heart’s rhythm (heartbeat) is regulated by natural electrical impulses that travel through the heart muscle. These impulses tell the heart’s chambers when to contract.

AV block occurs when some or all of the electrical signals traveling from the heart's upper chambers (the atria) to the lower chambers (the ventricles) are impaired or fail to transmit. AV block is also often called heart block. In this condition, the atria may contract at a normal rate, but the signals to the ventricles are “blocked.”

There are various types of AV block, depending on the mechanism of block. For example, second-degree AV block occurs when the electrical impulse from the atria occasionally does not pass through to the ventricles. In “complete AV block,” none of the normal electrical impulses from the atria pass through the atrioventricular node, leaving the ventricles to generate their own native rhythm, which is typically slower than the normal sinus rhythm. In babies born with complete AV block, this may be associated with long QT syndrome or maternal lupus.

A pacemaker, a small implanted device that stimulates the heart to beat at a certain rate, is a recommended treatment for significant AV block. However, some babies may be able to tolerate complete heart block well and may not require pacemaker implantation shortly after birth.

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