First-degree heart block: causes, ECG diagnosis and when it needs treatment

The heartbeat is controlled by electrical impulses. The British Heart Foundation explains that a heart block happens when these impulses are blocked or delayed. The most common type is AV (atrioventricular) heart block, in which the impulses are delayed or blocked as they travel between the atria, the top chambers of the heart, and the ventricles, the bottom chambers.

There are three degrees of AV heart block. First-degree is the mildest, and the NHS says it does not usually need treatment. Second-degree sometimes needs treatment and third-degree (complete) heart block often does. The word block can be misleading for first-degree, because the impulses are slowed rather than stopped.

The NHS describes heart block in general as a condition in which the heart beats too slowly or its heartbeat is not steady, which can happen if electrical impulses are blocked or delayed. In first-degree heart block this effect is small enough that most people do not notice anything.

First-degree heart block usually causes no symptoms. The British Heart Foundation says that second and third-degree heart blocks can cause symptoms, including feeling faint or dizzy, feeling tired and sometimes confused, feeling pressure or pain in the chest and being short of breath. The NHS lists dizziness, fainting or feeling about to faint, chest pain, tiredness and shortness of breath as possible symptoms of heart block in general, ranging from mild to severe depending on the type.

If you have been told you have first-degree heart block and then develop symptoms of this kind, it is sensible to seek advice, because symptoms suggest that something may have changed. The NHS says to get help from NHS 111 if you feel dizzy all the time or it keeps coming back, you have fainted, or you have shortness of breath that gets worse during normal activities or when you lie down. It adds that you are not wasting anyone's time by getting it checked.

The NHS says to call 999 if you have been diagnosed with heart block and have chest pain, severe difficulty breathing, feel sweaty, sick or lightheaded, or someone faints and is not breathing or cannot be woken within 1 minute. It advises not driving yourself to A&E.

The NHS says heart block is most often caused by a heart condition such as coronary heart disease or a heart attack. Babies are sometimes born with heart block, known as congenital heart block. Other causes of AV heart block listed by the NHS are taking some types of medicine, infection and inflammation of the heart caused by another condition, and having heart surgery. Sometimes there is no obvious cause.

The British Heart Foundation adds congenital heart disease, cardiomyopathy, ageing of the electrical pathways of the heart and thickening of the heart muscle to the list, and says heart block can also happen naturally in people with a normal heart and no heart problems. The specific cause depends on the type of block.

Because medicines can contribute, anyone told they have first-degree heart block should make sure the doctor reviewing their results has an up-to-date list of everything they take, including medicines bought without a prescription.

The NHS says the main test used to diagnose heart block is an electrocardiogram (ECG), which measures the electrical activity of the heart. It usually only takes a few minutes, but you may be asked to wear a portable ECG for 1 or 2 days to monitor the heart. The British Heart Foundation says the results of an ECG can show the type of heart block you have.

Other tests may be used to help diagnose heart block, according to the NHS: an echocardiogram or MRI scan to get a picture of the heart and nearby blood vessels, exercise tests to check the heart during a bike or treadmill test, and blood tests. These are usually used to look for an underlying heart condition rather than to confirm the block itself.

Because first-degree heart block rarely produces symptoms, the British Heart Foundation says heart block is often noticed during routine tests for other conditions. A finding on an ECG done for another reason is therefore a common way for people to learn about it.

The NHS says the treatment for heart block depends on what is causing it and whether you have any symptoms, and that if it is not causing symptoms you will not usually need treatment. For first-degree heart block this generally means being told what it is and when to seek help.

There are two reasons this matters. First, the British Heart Foundation says AV heart blocks might turn into higher degree blocks if they are left untreated, so follow-up advice from your doctor is worth following. Second, if the block is linked to a medicine or an electrolyte imbalance, the British Heart Foundation says treatment is directed at reversing the medicine effect or correcting the imbalance, with close monitoring in hospital if needed.

Pacemakers are generally reserved for more advanced block with symptoms. The British Heart Foundation says that if you are diagnosed with second or third-degree heart block you may need a pacemaker, while for first-degree no such treatment is usually needed.

Most people can carry on as normal. It helps to keep a note of the diagnosis, mention it to any doctor who prescribes medicines that affect the heart rhythm, and be aware of the symptoms described above. The NHS says you can get advice and support from your GP or other healthcare professionals, and information from the British Heart Foundation, which also runs a heart helpline staffed by cardiac nurses.

If your doctor suspects an underlying condition, such as coronary heart disease, treating that condition is part of managing the heart block. If you are worried about your treatment or have questions, the British Heart Foundation advises speaking to your doctor or healthcare team.

On the NHS, first-degree heart block found on an ECG is usually reviewed by a GP, and referred to a cardiologist only if there are symptoms, an underlying condition or other concerning findings. ECGs, echocardiograms and cardiology outpatient appointments are provided free at the point of use.

Some people choose a private cardiology review to discuss an incidental finding. The tests are the same ones described above, and a private cardiologist will usually want to see your existing ECG and a list of your medicines.