Heart Block

Heart block occurs when electrical signals from the upper chambers of the heart (atria) cannot travel to the lower chambers (ventricles). The ventricles then beat too slowly, decreasing the amount of oxygen that gets to the body and brain. This causes a slow pulse and can result in a lack of energy, feeling lightheaded or fainting. Heart block can be a cause of syncope. Pacemakers are commonly used to treat heart block.

What is Heart Block?

A normal heartbeat is initiated by an electrical signal that comes from the heart's natural pacemaker, the sinus node, located at the top of the right atrium. The electrical signal travels through the atria and reaches the atrioventricular (AV) node. After crossing the AV node, the electrical signal passes through the bundle of His. This bundle then divides into thin, wire-like structures called bundle branches that extend into the right and left ventricles. The electrical signal travels down the bundle branches and eventually reach the muscle cells of the ventricles, causing them to contract and pump blood to the body. Heart block occurs when this passage of electricity from top to bottom of the heart is delayed or interrupted.

The electrical impulses are slowed as they pass through the conduction system, but they all successfully reach the ventricles. First-degree heart block rarely causes symptoms or problems. Well-trained athletes may have first-degree heart block. Some medications can also cause this condition. No treatment is generally needed for first-degree heart block.

The electrical impulses are delayed further and further with each subsequent heartbeat until a beat fails to reach to the ventricles entirely. This type of block can is usually normal and is seen at rest and during sleep. It rarely causes symptoms of feeling light headed or dizzy.

With this condition, some of the electrical impulses from the atria are unable to reach the ventricles. This condition is less common than Type I, and is more serious. Usually, your doctor will recommend a pacemaker to treat type II second degree heart block, as it frequently progresses to third degree heart block.

Third-degree heart block, also called complete heart block, occurs when none of the electrical impulses from the atria reach the ventricles. When the ventricles (lower chambers) do not receive electrical impulses from the atria (upper chambers), they may generate some impulses on their own, called junctional or ventricular escape beats. Ventricular escape beats, the heart's naturally occurring backups, are usually very slow. Patients frequently feel fatigue, lightheaded, and notice decreased stamina. Patients are usually treated by implanting a permanent pacemaker.

With this condition, the electrical impulses are slowed or blocked as they travel through the specialized conducting tissue in one of the two ventricles. This type of block is detected on the electrocardiogram or ECG and does not usually cause any symptoms.

Symptoms & Signs

Some people with heart block will not experience any symptoms. Others will have symptoms that may include the following:

  • Fatigue/excessive tiredness
  • Fainting (syncope)
  • Dizziness
  • Feeling lightheaded
  • Short of breath
  • Decline in exercise capacity
  • Pain, pressure, tightness, or discomfort in your chest
  • Trouble with everyday exercises or activities

Risk Factors

Some medical conditions increase the risk for developing heart block. These medical conditions include:

  • Heart failure
  • Prior heart attack
  • Heart valve abnormalities
  • Heart valve surgery
  • Congenital heart diseases
  • Some medications or exposure to toxic substances
  • Lyme disease
  • Aging

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