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Heart Block

Electrical signals control the beating of your heart. They tell your heart muscle when to contract, a process known as conduction. The normal timing of heartbeats is generated in the upper chamber of the heart (atria) in a structure called the sinus node. The signal moves from the sinus node to the pumping chambers (ventricles) of the heart to cause a heartbeat (contraction). When you have heart block, there is interference with the electrical signals that usually move from the atria to the ventricles. This is known as a conduction disorder. If the electrical signals can’t move from your atria to your ventricles, they can’t tell your ventricles to contract and pump blood correctly.

In most cases of heart block, the signals slow down, but don’t completely stop. Heart block is called first-, second-, or third-degree:

  • First-degree heart block is the least severe. The electrical signals slow down as they move from your atria to your ventricles. You may not need any treatment for first-degree heart block.
  • Second-degree heart block means that the electrical signals between your atria and ventricles can intermittently fail to conduct. There are 2 types of second-degree heart block
    • Mobitz type I: The electrical signals get slower and slower between beats. Eventually your heart drops a beat.
    • Mobitz type II: The electrical signals sometimes get to the ventricles, and sometimes they don’t. There is no progressive slowing of the electrical signal. This type of heart block can often progress to third-degree heart block.
  • Third-degree heart block is the most severe. Electrical signals don’t go from your atria to your ventricles at all with this type. There is a complete failure of electrical conduction. This can result in no pulse or a very slow pulse if a back up heart rate is present.

What causes heart block?

If you are born with heart block, it’s called congenital heart block. It is caused by a condition your mother had during her pregnancy or heart problems you were born with.

For most, heart block develops as you get older. It happens as the wires (nerve fibers) that connect the top and bottom of the heart develop fibrosis and eventually fail. Sometimes this may happen because of advancing age. Any process that can damage these heart wires can result in heart block. Coronary artery disease with and without a heart attack is one of the most common causes of heart block. Diseases that weaken the heart muscle (cardiomyopathies) can also damage the wire. Heart block can also be caused by any disease that can affect the heart such as sarcoidosis and certain cancers, or any disease that results in heart inflammation. This can be an autoimmune disease or infections. Electrolyte problems such as high potassium levels can also result in heart block.

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