Heart block

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. Heart block is a type of arrhythmia (irregular heartbeat).

Animation – The different types of arrhythmia
About heart block
Symptoms of heart block
Complications of heart block
Causes of heart block
Diagnosis of heart block
Treatment of heart block

Animation – The different types of arrhythmia

The information on the video provided does not constitute advice on diagnosis or the treatment for heart disease and such advice should always be sought from a doctor or another suitably qualified health professional.

About heart block

Your heart is responsible for delivering the oxygen in your blood to your body, by pumping it through your blood vessels. When your heart beats too slowly, it can't do this as efficiently. The usual heart rate for adults is between 60 and 100 beats per minute. Your heartbeat is considered to be too slow if it drops below 50 beats per minute. This can lead to symptoms such as fainting and breathlessness.

What happens in heart block?

Your heartbeat is controlled by electrical signals (impulses) that travel through your heart to make it contract. These impulses start in a part of the heart wall called the sinus node. They then travel from the atria (the upper chambers of your 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, it means there is 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, which are described below.

•    First-degree – the electrical signals are slowed as they pass through the AV node. You will rarely have 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 other signal is blocked. This type of heart block may cause you symptoms such as dizziness and fainting, but you may not have any symptoms.
•   Third-degree (complete heart block) – this is the most serious type of heart block. It's often found in adults who already have 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). You will usually have a very slow heartbeat (bradycardia) and it can cause you to have blackouts.

Heart block can also occur in the specialised group of electrical-conducting muscle fibres (the bundle of His) that come out of 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. If you have right bundle branch block, you probably won't have any symptoms. Left bundle branch block is more often the result of a heart problem, such as high blood pressure.

Symptoms of heart block

Whether or not you have any symptoms from 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:
•    dizziness
•    fainting or nearly fainting
•    chest pain
•    breathlessness following exercise or activity

These symptoms may be caused by problems other than heart block, but if you have them see a doctor for advice.

Complications of heart block

Most people who have heart block don't develop complications. However, it's possible for heart block to lead to heart failure or blackouts.

Causes of heart block

Causes of heart block include:
•    older age – it mostly occurs in people over 65
•    coronary artery disease
•    certain medicines (including beta-blockers, digoxin, verapamil and amiodarone)
•    diseases of the heart muscle, for example sarcoidosis
•    certain infectious diseases (such as Lyme disease)
•    some other diseases (such as rheumatoid arthritis and systemic lupus erythematosus)
•    congenital disorders (conditions you're born with)

Diagnosis of heart block

Heart block is often found by chance if you have 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 and do tests to find out if any underlying disease or condition, such as an underactive thyroid, is causing your symptoms.

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 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 tests to confirm your diagnosis.

•    Blood tests – to check for underactive thyroid.
•    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 and rhythm.
•    Tilt-table – to see whether or not a slow heart rate is triggered by a change in your posture (a condition known as postural hypotension or vasovagal syndrome).

Please note that availability and use of specific tests may vary from country to country.

Treatment of heart block

Treatment depends on how severe your heart block is. If your heart block is mild, was 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're taking, your doctor can review them. If it's caused by an underlying condition, that will be the focus of your treatment.

If your heart block is more severe, but not caused by medicines or an underlying condition, you will probably need 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 of your chest. It monitors your heartbeat and produces electrical signals to stimulate your heart to contract. A pacemaker sends out signals only when your 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 in your heart – usually your right atrium and right ventricle.

If your doctor thinks you need a pacemaker urgently – because of the risks of having a low heart rate – you may have a temporary pacemaker put in until you're able to have a permanent one fitted. This involves threading a wire into your heart, starting from a vein in your groin or neck.

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

You may 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 your wound to heal and you may be given an appointment during this time to have your stitches removed. However, this varies between individuals and with the technique used to fit your pacemaker, so it's important to follow your doctor's advice.

Details of the procedure may vary from country to country.

Produced by Krysta Munford, Bupa Health Information Team, July 2012.