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What Causes Heart Block?

Heart block has many causes. Some people are born with the disorder (congenital), while others develop it during their lifetimes (acquired).

Congenital Heart Block

One form of congenital heart block occurs in babies whose mothers have autoimmune diseases, such as lupus. People who have these diseases make proteins called antibodies that attack and damage the body's tissues or cells.

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

Congenital heart defects also may cause congenital heart block. These defects are problems with the heart's structure that are present at birth. Often, doctors don't know what causes these defects.

Acquired Heart Block

Many factors can cause acquired heart block. Examples include:

  • Damage to the heart from a heart attack. This is the most common cause of acquired heart block.
  • Coronary heart disease, also called coronary artery disease.
  • Myocarditis (MI-o-kar-DI-tis), or inflammation of the heart muscle.
  • Heart failure.
  • Rheumatic (roo-MAT-ik) fever.
  • Cardiomyopathy (KAR-de-o-mi-OP-a-the), or heart muscle diseases.

Other diseases may increase the risk of heart block. Examples include sarcoidosis (sar-koy-DOE-sis) 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, beta blockers, and calcium channel blockers—also may cause heart block. Doctors closely watch people who are taking these medicines for signs of problems.

Some types of heart block have been linked to genetic mutations (changes in the genes).

An overly active vagus nerve also can cause heart block. You have one vagus nerve on each side of your body. These nerves run from your brain stem all the way to your abdomen. Activity in the vagus nerve slows the heart rate.

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 during recovery.

Also, if a medicine is causing heart block, the disorder may go away if the medicine is stopped or the dosage is lowered. Always talk with your doctor before you change the way you take your medicines.

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Updated: July 9, 2012