Most faints are not caused by heart disease. The most common type is a simple or vasovagal faint, where a trigger such as standing for a long time, heat, pain or the sight of blood causes a sudden drop in heart rate and blood pressure. These faints are usually harmless. However, fainting can also be a sign of a heart rhythm problem, such as a very slow or very fast heartbeat, or a structural problem such as a narrowed heart valve or thickened heart muscle.

The details of the faint usually point to which is more likely. Fainting during exercise, fainting while lying down, fainting with no warning at all, or fainting with chest pain or palpitations beforehand are the warning signs that a heart cause needs to be ruled out promptly. The NHS advises that anyone who has fainted should see their GP, and certain patterns need a cardiology assessment within days rather than weeks.

Why fainting happens

A faint, also called syncope, is a brief loss of consciousness caused by a temporary drop in blood flow to the brain. The brain needs a constant supply of oxygen, so even a few seconds of reduced blood flow is enough to cause you to collapse. Once you are lying flat, blood flow to the brain returns and you usually come round within a minute.

The question for a doctor is always why blood flow dropped. Broadly, there are three groups of cause.

1. Reflex faints, where the nervous system briefly overreacts and slows the heart or widens the blood vessels.
2. Postural faints, where blood pressure falls when you stand up.
3. Cardiac faints, where the heart itself cannot keep up the pumping needed to supply the brain.

Faints that are usually not heart related

Vasovagal or reflex syncope

This is by far the most common type of faint. Typical triggers include standing for long periods, hot or crowded places, pain, emotional upset, the sight of blood or needles, and dehydration. There are usually warning signs beforehand, such as feeling hot, sweaty, nauseous or light-headed, with blurred or tunnel vision.

Situational faints belong in this group too. Some people faint when coughing, passing urine at night or straining on the toilet.

Postural hypotension

Some people feel dizzy or faint when they stand up quickly because their blood pressure does not adjust fast enough. This is more common in older people, those who are dehydrated, and people taking blood pressure medicines or diuretics.

From working with patients across Kent and East Sussex since 2006, we’ve found that reviewing medication is one of the most useful first steps for older patients who faint. Blood pressure tablets that were right a few years ago can become too strong as people age or lose weight, and a simple adjustment can stop the faints altogether.

Heart conditions that can cause fainting

Slow heart rhythms

If the heart’s electrical system fails to pass signals from the upper to the lower chambers, the heart rate can suddenly drop very low or even pause for several seconds. This is known as heart block. Sick sinus syndrome, where the heart’s natural pacemaker becomes unreliable, can have a similar effect. These faints often happen with little or no warning. Treatment is usually a permanent pacemaker, which prevents the heart rate from falling too low.

Fast heart rhythms

A very fast heart rhythm can mean the heart does not have time to fill properly between beats, so it pumps less blood. Supraventricular tachycardia occasionally causes fainting, but the more serious concern is ventricular tachycardia, a fast rhythm starting in the lower chambers. This is more likely in people with a previous heart attack, a weakened heart muscle or an inherited rhythm condition.

Aortic stenosis

The aortic valve controls blood flow out of the heart to the rest of the body. When it becomes narrowed, the heart cannot increase its output enough during exertion, and blood pressure can fall. Fainting during exercise, together with breathlessness or chest tightness, is a classic warning sign. Severe aortic stenosis is treated with valve replacement, either through surgery or a less invasive procedure called TAVI.

Hypertrophic cardiomyopathy

In this inherited condition the heart muscle becomes abnormally thick. In some people the thickened muscle partly blocks blood flow out of the heart, and it can also cause dangerous heart rhythms. It is one of the conditions doctors look for when a young person faints during sport.

Inherited rhythm conditions

Conditions such as long QT syndrome and Brugada syndrome affect the heart’s electrical system and can cause fainting, sometimes triggered by exercise, sudden noise or emotion. They can run in families, which is why a family history of sudden death under the age of 40 is always taken seriously.

Warning signs that point to a heart cause

The NHS advises calling 999 if someone has fainted and has chest pain or a pounding or irregular heartbeat, cannot be woken within a minute, or fainted while exercising or while lying down.

Guidance from NICE on blackouts goes further. It recommends that everyone who has had an unexplained loss of consciousness has a 12-lead ECG, and that people with certain features are seen by a specialist within 24 hours. Those features include the following.

• An abnormal ECG
• A known heart condition, including heart failure
• Fainting during exertion
• A family history of sudden cardiac death under the age of 40 or an inherited heart condition
• New or unexplained breathlessness
• A heart murmur

In our experience, an accurate account from someone who saw the faint works better than any single test for deciding where to start, because it tells us how quickly the person went down, whether they went pale, how long they were unconscious and how fast they recovered. We always encourage patients to bring a witness to the appointment or to note what they saw.

How fainting is investigated

The right tests depend on the story and the examination, but a cardiology assessment usually draws on the following.

• An ECG, which can show signs of heart block, inherited rhythm conditions or a previous heart attack.
• An echocardiogram, which checks the valves and heart muscle and can identify aortic stenosis or cardiomyopathy.
• A 24 hour ECG or 7-day cardiac event recorder, to look for rhythm problems that come and go.
• An exercise stress test, particularly if the faint happened during exertion.
• A tilt test, which recreates the conditions of a reflex faint under controlled monitoring and helps confirm vasovagal syncope or postural problems.

We’ve found that a tilt test is particularly valuable for younger patients who have had several unexplained faints. Seeing a faint reproduced safely, with the heart rate and blood pressure recorded, often gives a clear diagnosis and the reassurance that nothing more serious is going on.

Fainting and driving

If you have fainted, you may need to stop driving and tell the DVLA, depending on the cause and whether it is likely to happen again. The government advises that you must tell the DVLA if your condition affects your driving, and you can be fined up to £1,000 if you do not. Your doctor can tell you which rules apply to you.

Seeing a cardiologist about fainting

At our Warwick Park practice in Tunbridge Wells, ECGs, echocardiograms, exercise tests, 24 hour monitoring and tilt testing are all available through our practice, most of them at our own rooms, so fainting assessments can usually be completed close to home. If a pacemaker or valve treatment is needed, our consultants carry out these procedures at local hospitals, and they also hold NHS consultant posts at Tunbridge Wells Hospital.

Conclusion

Fainting is most often caused by a harmless reflex, but it can be a sign of a heart condition such as heart block, a fast heart rhythm, aortic stenosis or hypertrophic cardiomyopathy. Fainting during exercise, while lying down, without warning or with chest pain or palpitations needs prompt medical assessment.

If you or a family member has fainted and the cause is not clear, West Kent Cardiology Partnership can arrange the tests needed to find out why. Contact us or call 01892 526726 to book an appointment.