Second-degree heart block

Second-degree AV heart block happens when the electrical signals that tell your heart to contract don't always pass between the top and bottom chambers of your heart as they should. This causes an abnormal heart beat (arrhythmia).

What is second-degree heart block?

  • When a healthy heart beats, an electrical impulse travels through the top chambers of the heart (atria) to the bottom chambers (ventricles). This impulse causes the chambers of the heart to beat and push blood through and out of the heart.
  • If you have second-degree heart block, the electrical impulses will sometimes fail to reach the lower chambers of your heart.
  • This can cause your heart to skip beats, affecting the flow of oxygen-rich blood to your body and brain

What are the types of second-degree heart block?

There are two types of second-degree heart block:

  • second-degree type 1 heart block, also known as Mobitz I
  • second-degree type 2 heart block, also known as Mobitz II

If you have second-degree type 1 heart block, or Mobitz I, your heart will skip beats in a regular pattern.  Your body can usually cope well with this, so you won't usually experience any symptoms.

If you have second-degree type 2 heart block, or Mobitz II, your heart will skip beats in an irregular pattern.  Your body can't compensate for this and this type of heart block can lead to light-headedness, dizziness and fainting.

Find out more about different types of heart block

What causes second-degree heart block?

Most people with second-degree heart block have an underlying heart condition like coronary heart diseasecardiomyopathy or congenital heart disease

It can also be caused by ageing of the electrical pathways in your heart (meaning you're more likely to get it if you're older), electrolyte imbalances, and some medicines.

What are the tests and treatments for second-degree heart block?

Your doctor might recommend that you undergo an ECG to help diagnose second-degree heart block.

  • If you're an adult with second-degree heart block that causes you to have a very slow heart rate, it's likely your doctor will suggest that you have a pacemaker fitted.
  • If you have second-degree heart block that was caused by a heart attack, you may need only a temporary pacemaker. If a normal heart rhythm hasn’t returned a few weeks after your heart attack, you might need to have a permanent pacemaker fitted.
  • If you're a young person with congenital heart disease with second-degree or third-degree heart block but you don’t have a slow heart rate or any symptoms, you may not need a pacemaker. 

Heart rhythms booklet

This booklet describes the heart's normal rhythm and various abnormal rhythms as well as explaining how they're diagnosed and treated.

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