Heart block

Published by Bupa's Health Information Team, June 2010.

This factsheet is for people who have heart block, or who would like information about it.

Heart block causes your heartbeat to slow down or beat irregularly. It happens when the electrical signals that control your heartbeat are slowed down or blocked as they travel through your heart. It's mostly caused by old age or heart disease. Heart block is a type of arrhythmia (irregular heartbeat).

The different types of arrhythmia

          A Flash plug-in is required to view this animation.

About heart block

Your heart is responsible for delivering oxygen to your body through your bloodstream. When your heart beats too slowly, it can't do this as efficiently. This can lead to symptoms such as fainting and black-outs.

What happens in heart block?

Your heartbeat is controlled by electrical signals (impulses), which start in a part of the heart wall called the sinus node and travel through the heart making it contract. The signals travel from the atria (the upper chambers of the heart) to the ventricles (the lower chambers) through an area called the atrioventricular (AV) node. The AV node helps to synchronise the pumping action of the atria and ventricles.

If you have heart block, there's a problem affecting how these electrical signals are transmitted through your heart. When the problem occurs at the AV node, it prevents the signals being conducted from the atria to the ventricles. This is called AV block. There are three different degrees of AV block.

• First-degree - the electrical signals are slowed as they pass through the AV node. There are rarely any symptoms.
• Second-degree - not all electrical signals reach your ventricles. The signals can sometimes become increasingly delayed until one is blocked altogether, or it may be that every third or fourth signal is blocked. This type of heart block causes symptoms such as dizziness.
• Third-degree (complete heart block) - this is the most serious type of heart block. It's most common in adults with heart disease. It occurs when no electrical signals reach the ventricles from the atria and the ventricles end up producing their own electrical signals (called the escape rhythm). It usually results in a very slow heartbeat (bradycardia) and can cause a heart attack.

A heart block can also occur in the specialised group of electrical-conducting muscle fibres (the bundle of His) that emerge from the AV node, divide and lead into the right and left ventricles. This is called bundle branch block. It can affect the left- or right-hand side of your heart. Right bundle branch block (RBBB) doesn't normally produce any symptoms. Left bundle branch block (LBBB) is the result of a heart problem such as ischaemic heart disease.

Symptoms of heart block

Whether or not you have any symptoms from a heart block depends on the type of heart block you have and how severe it is. If the heart block has caused your heart rate to slow down (especially if it's less than 40 beats per minute), you may have the following symptoms:

• dizziness
• fainting or nearly fainting
• chest pain
• breathlessness following exercise/activity
• seizures, caused by not enough oxygen getting to the brain

These symptoms may be caused by problems other than heart block. If you have any of these symptoms, see your doctor for advice.

Complications of heart block

Not everyone who has heart block develops complications; however it's possible for heart block to lead to a stroke or heart attack.

Causes of heart block

Causes of heart block include:

• coronary artery disease
• certain medicines (including beta-blockers, digoxin, verapamil and amiodarone)
• diseases of the heart muscle
• heart attack
• certain infectious diseases (such as Lyme disease)
• some other diseases (such as rheumatoid arthritis and systemic lupus erythematosus)
• inherited (congenital) disorders

Diagnosis of heart block

Heart block is often found by chance when having tests for other problems. Your doctor will ask about your symptoms and examine you. He or she may also ask you about your medical history.

Some medicines such as beta-blockers, can slow down your heart rate. Your doctor will review any medicines that you're taking to make sure they're not causing your heart block.

Your doctor will do tests to find out if any underlying disease or condition such as anaemia or poor liver function is causing your symptoms.

Your doctor may refer you to a cardiologist for further tests. A cardiologist is a doctor specialising in conditions affecting the heart.

You may have the following hospital tests to confirm diagnosis.

• Blood tests - to check for anaemia and liver function.
• Electrocardiogram (ECG) - measures the electrical activity in your heart to see how well it's working.
• Echocardiogram - uses ultrasound to produce a clear image of your heart muscles and valves.
• 24-hour heart monitor - to record your heart rate.
• Electrophysiology - to discover which part of your heart is responsible for heart block.
• Tilt-table - to check for an abnormal rhythm by using changes in your position.
• MRI scan - uses powerful magnets, radio waves and digital technology to produce detailed images of your heart muscles and valves.

Treatment of heart block

Treatment depends on how severe your heart block is. If your heart block has been discovered by chance and you don't have any symptoms, you probably won't need any treatment.

If your heart block is caused by medicines you are taking, they can be reviewed; if it is caused by an underlying condition, it can be treated.

If your heart block is more severe but not caused by medicines or an underlying condition, the main treatment is to have a pacemaker fitted.

Pacemaker implantation

A pacemaker is a small device, about the size of a matchbox, usually implanted near your collarbone on the left side. It monitors your heartbeat and produces electrical signals to stimulate the heart to contract and produce a heartbeat. A pacemaker either sends out signals constantly at a fixed rate, or only when the heartbeat slows.

The pacemaker is connected to your heart by one or more leads, which are passed through a vein to your heart. For heart block, pacemakers with two leads (called dual-chamber pacemakers) are normally used. The two leads connect to two different points of your heart - usually your right atrium and right ventricle.

If your doctor thinks you need a pacemaker immediately, you may have a temporary pacemaker inserted until you're able to have a permanent pacemaker. This involves threading a wire into your heart, which keeps it pumping regularly.

You will probably have your pacemaker fitted under sedation and local anaesthesia. This means all feeling from the area where the pacemaker is being inserted will be blocked and you will feel relaxed, but stay awake during the procedure.

You will usually be able to go home the day after your procedure, once your doctor has checked that the pacemaker is working correctly. It usually takes about six weeks for the wound to heal, but this varies between individuals, so it's important to follow your doctor's advice.

For answers to frequently asked questions on this topic, see FAQs.

For sources and links to further information, see Resources.