Introduction of Heart block

A heart block is when electrical pulses that control the beating of the heart are disrupted.

There are three levels of heart block and usually only the most serious type of heart block causes symptoms. This type of heart block is known as a complete, or third degree, heart block. 

Symptoms of heart block can include:

• shortness of breath
• palpitations (irregular heartbeat)
• fainting

Unless you are experiencing symptoms, heart block is often diagnosed during routine tests for other conditions. Babies may be diagnosed with the condition during pregnancy.

Read more information about diagnosing heart block.

How the heart beats

When the heart beats, the heart muscle contracts (pulls inwards) in preparation for pumping blood around the body. The contractions are triggered by electrical pulses  generated by a selection of specialised cells known as the sinoatrial node (SA node).

The SA node, also known as the pacemaker, generates electrical pulses at regular intervals. The pulse is sent to a group of cells known as the atrioventricular node (AV node) which relays the pulse to the two lower chambers of the heart (the ventricles).

A heart block occurs if the transmission of the pulse between the SA node, the AV node and the ventricles is interrupted.

A heart block does not mean that the heart stops beating altogether – other ‘back-up’ systems take over. However, it can result in an abnormally slow heartbeat (bradycardia), which deprives the body’s organs and tissue of oxygen.

What causes heart block?

Some people are born with heart block, either because of a heart defect or genetic condition. This is known as a congenital heart block.

Heart block can also be caused by:

• conditions such as a heart attack
• certain infections such as diptheria
• certain medicines
• having open heart surgery

This is known as acquired heart block.

Read more about the causes of heart block.

There are three main types of heart block:

• first degree heart block
• second degree heart block
• third degree heart block

These are described in more detail below.

First degree heart block

In first degree heart block there is a split-second delay in the time that it takes electrical pulses to move through the AV node. First degree heart block rarely causes noticeable symptoms.

Second degree heart block 

In second degree heart block there is a series of increasing delays in the time that it takes the AV node to send the pulse to the ventricle. Eventually, a heartbeat is skipped.

There are two sub-types of second degree heart block:

• Mobitz type 1 – this is the less serious type; it may occasionally cause mild dizziness and does not usually require treatment. It is more commonly known as Wenckeback second degree AV block
• Mobitz type 2 – this is a more serious type; it may cause light headedness, dizziness and fainting, and usually requires treatment

Third degree heart block

In third degree or complete heart block there is no transmission of electrical pulses between the atria and the ventricles through the AV node.

A third degree heart block causes a wide range of symptoms, some of which are life-threatening. This type of heart block may be a medical emergency but in many cases may be benign and does not always require treatment.

How is heart block treated?

Heart block does not always require treatment, unless there are serious symptoms. However, acquired heart block usually needs treatment.

Transcutaneous pacing (TCP) uses electrical pulses to help stabilise your heartbeat and is the main treatment for heart block.

More serious cases will often require a pacemaker. A pacemaker is a small battery-operated device which is inserted under the skin of your chest. It sends regular electrical pulses to keep your heart beating regularly.

Treatment for heart block works well if given when required. Deaths caused by these conditions are rare.

Read more information about how heart block is treated.

Who is affected?

First degree and Mobitz type 1 heart blocks are uncommon but not rare. It is estimated that up to two out of 100 otherwise healthy adults have these types of heart blocks.

Mobitz type 2 heart block is rare in the general population, but more common in people with certain heart conditions. For example, an estimated one in 30 people with heart failure will develop Mobitz type 2 heart block.

Congenital third degree heart blocks are rare, occurring in one in every 20,000 births.

Conversely, acquired third degree heart block is a common complication of heart disease, particularly in older people. It is estimated that 5-10% of people over 70 years old who have a history of heart disease will develop a third degree heart block.