Heart Block

Basic Facts

  • Heart block is an abnormality of the spread or flow of electrical activity from the upper heart chambers, the atria, to the lower chambers of the heart, the ventricles.
  • Heart block results in an abnormality or disturbance in the rate or rhythm of the heartbeat.
  • Heart block occurs in three levels of severity. First-degree block is a delay of the signal that stimulates the ventricles to contract, second-degree block is a partial or intermittent interruption of the signal that stimulates the ventricles to contract, and third-degree block is a complete interruption of the signal that stimulates the heart to contract.
Heart block is a disorder of impulse conduction, meaning that an electrical impulse is impaired from traveling along its normal pathway.

 

Heart block symptoms can vary according to its type, frequency, duration, and whether underlying structural heart disease is present. Heart block can contribute to bradyarrhythmia, or an arrhythmia that causes an abnormally slow heart rate (fewer than 60 beats per minute). People with bradyarrhythmia may experience the following:

  • Dizziness or light-headedness
  • Low blood pressure
  • Palpitations (the sensation of skipped beats)
  • Fatigue
  • Syncope (fainting)
  • Sudden death

Heart block may occur at any age, but commonly becomes more frequent during middle age and is associated with aging. Among people without heart disease, the exact cause of heart block may be unknown. Milder forms of heart block may be caused by certain medications, including:

  • Adenosine,
  • Calcium channel blockers,
  • Beta-blockers, and
  • Digitalis.

Certain diseases can cause heart block, including:

  • Endocarditis (inflammation of the tissue that lines the heart),
  • Myocarditis (inflammation of heart muscle tissue),
  • Lyme disease,
  • Lenegre disease,
  • Lev disease,
  • Coronary heart disease,
  • Heart attack,
  • Sarcoidosis, and
  • Muscular dystrophy.

Some kinds of heart block can be caused by what physicians call increased vagal tone, which occurs when the vagus nerve, which controls involuntary bodily functions including hear rate, is stimulated, causing an abnormally slow heart rate. Heart block, especially in children, may also be congenital, meaning present when a person is born. People who have undergone corrective heart surgery may also develop heart block.

Because heart block may be unpredictable and brief, the condition can be difficult to diagnose. In addition to taking a person's medical history, listening to the patient describe symptoms, and conducting a physical examination, the physician will use on of the following tests:

  • Electrocardiogram (ECG)- This noninvasive test records the electrical activity of the heart.
  • Holter Monitor- This device records the heart's activity for 24 hours or longer.
  • Event recorder- This portable ECG can be activated when a patient experiences symptoms of a fast heart rate. It is intended to monitor heart activity over a few weeks or months. 
  • Implantable loop recorder- This implanted recorder can be used to diagnose patients with recurring and unexplained arrhythmia episodes.

A person's heart block may resolve naturally. In some cases, heart block may not be frequent, sustained, or bothersome enough to require treatment. 

Other forms of heart block can be controlled once the underlying heart disease is treated. For example, in people who take a heart medication that may cause heart block, physicians may discontinue the use of the drug. When a person develops complete following a heart attack, for example, the heart block may resolve with the healing of the area of heart muscle affected by the heart attack. 

Common medications for heart block include atropine and isoproterenol. These drugs may be used in the short term to treat a slow heart rate that causes symptoms, but second and third degree heart block may be unresponsive.

More severe forms of heart block that cause symptoms may require treatment, including pacing, which is the use of a pacemaker for electrical stimulation of the heart.