Heart Block Types

A heart block is an abnormal heart rhythm (arrhythmia) that happens when the electrical impulses that tell your heart when to beat are delayed or blocked as they travel through your heart. Some heart blocks will not cause any symptoms but others are more serious.

There are three main types of heart block:

  1. AV (atrioventricular) heart blocks
  2. Bundle branch blocks
  3. Tachybrady syndrome

AV (atrioventricular) heart blocks

An AV heart block happens when the electrical impulses are delayed or blocked as they travel between your atria (the top chambers of your heart) and your ventricles (the bottom chambers of your heart).

There are three ‘degrees’ of AV heart block:

  1. First-degree heart block, which usually doesn’t cause symptoms or need treatment
  2. Second-degree heart block
  3. Third-degree (complete) heart block

AV heart block can be caused by coronary heart disease, congenital heart disease, cardiomyopathy, ageing of the electrical pathways in your heart, and some medicines. The type of treatment you’ll need will depend on the cause and symptoms. Some AV heart blocks may develop into higher degree AV heart blocks if they're left untreated. Your doctor will be able to give you advice about this.

Some people always have AV heart block but in others the condition can come and go.

Bundle branch blocks

Bundle branch blocks happen when the electrical impulses travel through the bottom chambers of your heart (your ventricles) more slowly than normal because of a block in the electrical pathway. Bundle branch blocks will always cause symptoms and could be a sign of an underlying heart condition which you might need treatment for.

There are two types of bundle branch blocks:

Left bundle branch block

Left bundle branch block is usually caused by an underlying condition such as coronary heart diseasecardiomyopathy,  thickening of the heart muscle (left ventricular hypertrophic cardiomyopathy) or ageing of the electrical pathway in your heart.

Right bundle branch blocks

Right bundle branch block can be caused by coronary heart diseasecongenital heart disease, or some lung conditions.  However it can also happen naturally in people with a normal heart and no heart problems.

Tachybrady syndrome

Tachybrady syndrome happens when your heart’s sinus node doesn’t work properly. Your sinus node (sometimes called your heart’s natural pacemaker) is responsible for telling your heart when to beat. If your sinus node doesn’t work properly, it can cause your heartbeat to become too fast or too slow, or switch between fast and slow rhythms. An example of this is when atrial flutter (a fast heart rhythm) alternates with a slow heart rhythm.

There might also be sudden pauses in the electrical activity in your heart, which could lead to you feeling dizzy, lightheaded, or sometimes collapsing.

The most likely cause of tachybrady syndrome is ageing of the electrical pathway in your heart but it can also be caused by coronary heart disease, for example after a heart attack, and some medicines. If you have tachybrady syndrome you might need a combination of medicines or have a pacemaker fitted.

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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