What causes a heart block?

Indrajit Choudhuri, MD
Cardiology (Cardiovascular Disease)

Heart block is NOT a blockage in the coronary arteries (arteries of the heart). Rather, it refers to abnormal prevention of normal ELECTRICAL conduction, i.e. conduction block. "Heart block" can result from many causes including medicines, acute heart attack, cardiac surgery, Lyme disease, objects inside the heart that can traumatize the normal conduction system, progressive inflammation and scarring inside the heart (fibrosis), and many other causes.

Heart block occurs when the electrical signals created in the heart’s upper chambers don’t reach the lower chambers, causing the heart to beat too slowly.

Heart block has a number of causes. You can be born with this disorder (congenital) or acquire it.

Congenital heart block

One form of congenital heart block occurs in the babies of women who have autoimmune diseases, such as lupus. People who have these diseases make proteins called antibodies.

In pregnant women, these antibodies can cross the placenta. (The placenta is the organ that attaches the umbilical cord to the mother's womb.) They can damage the baby's heart and lead to congenital heart block.

Congenital heart defects (problems with heart's structure) also may cause congenital heart block. Often, doctors don't know what causes these defects.

Acquired heart block

A number of factors, such as diseases, surgery, medicines, and other conditions, can cause acquired heart block.

The most common cause of acquired heart block is damage to the heart from a heart attack. Other diseases that can cause heart block include coronary artery disease, myocarditis (inflammation of the heart muscle), heart failure, rheumatic fever, and cardiomyopathy.

Other diseases may increase the risk for heart block. These include sarcoidosis and the degenerative muscle disorders, Lev's disease and Lenegre's disease.

Certain types of surgery also may damage the heart's electrical system and lead to heart block.

Exposure to toxic substances and taking certain medicines, including digitalis and beta blockers, also may cause heart block. Doctors closely watch people who are taking these medicines for signs of problems.

In some cases, atrioventricular (AV) heart block has been linked to genetic mutations (changes in the genes).

An overly active vagus nerve can cause first-degree heart block. Activity in this nerve slows the heart rate. Well-trained athletes and young people are at higher risk for first-degree heart block due to this cause.

In some cases, acquired heart block may go away if the factor causing it is treated or resolved. For example, heart block that occurs after a heart attack or surgery may go away after recovery.

Also, if a medicine is causing heart block, the condition may go away if the medicine is stopped or the dosage is lowered. However, you shouldn't change the way you take your medicines unless your doctor tells you to.

This answer from the National Heart, Lung and Blood Institute has been reviewed and/or edited by Dr. William D. Knopf.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.