Fainting caused by the heart (cardiac syncope): causes, tests and treatment

Syncope is the medical word for fainting, a short loss of consciousness. The NHS describes fainting as when you pass out for a short time, and notes that the person usually wakes up within about 30 seconds. NICE uses the broader term transient loss of consciousness, or "blackouts", in its guideline CG109, and sets out how to tell the different causes apart.

Many faints are not related to the heart: the NHS lists standing up too quickly, not eating or drinking enough, being too hot and being very upset or in severe pain, and NICE describes the common uncomplicated (vasovagal) faint. Arrhythmogenic syncope is different: it happens when the heart beats too fast, too slowly or irregularly so that not enough blood reaches the brain for a moment. The NHS explains that a heart rhythm problem (arrhythmia) can make your heart beat too quickly, too slowly or unsteadily, and that this can make you feel lightheaded, dizzy or like you might faint.

Because a rhythm-related faint can occasionally signal a condition that needs treatment, doctors take the history and a heart tracing seriously even when the person feels completely well afterwards.

The NHS advises calling 999 if someone who has fainted is not breathing, cannot be woken within 1 minute, has not fully recovered or has difficulty with speech or movement, has chest pain or a pounding, fluttering or irregular heartbeat, has seriously hurt themselves, is shaking or jerking, fainted while exercising, or fainted while lying down. Do not drive yourself to A&E.

NICE guideline CG109 lists features that lead to urgent cardiovascular assessment, with the referral reviewed by a specialist within 24 hours. These are:

• An abnormal ECG, such as a conduction abnormality, a long or short QT interval, or ST segment or T wave abnormalities.

• A history or signs of heart failure.

• A blackout 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.

• NICE also says to consider referral within 24 hours for anyone over 65 who has a blackout without any warning symptoms beforehand.

NICE describes an uncomplicated faint (vasovagal syncope) as one with a typical posture, provoking factor and prodromal symptoms: prolonged standing or episodes prevented by lying down, a trigger such as pain or a medical procedure, and warning signs such as sweating or feeling warm or hot. When these are present and nothing suggests another diagnosis, no further immediate management is usually required.

The NHS lists similar warning symptoms of an ordinary faint: dizziness, sweating, feeling warm or hot, feeling sick and changes to vision. Features that make clinicians look harder for a heart cause include a faint during exercise, a faint with palpitations or chest pain, a family history of sudden cardiac death or inherited heart conditions, and, in people over 65, a blackout without warning symptoms.

Witnesses are very helpful. NICE recommends that clinicians ask the person and any witnesses what happened before, during and after the event, including posture, colour, any limb-jerking and how long it lasted, and advises people to record future events on video or with a detailed account if the diagnosis is unclear.

The first step is a 12-lead ECG, which the NHS describes as a test that records the electrical activity of the heart, including its rate and rhythm. It is usually quick and painless, with sticky patches placed on the arms, legs and chest. NICE also recommends checking lying and standing blood pressure and reviewing medicines that may have contributed.

For a blackout that happened during exercise, NICE says to offer urgent exercise testing (within 7 days) unless there is a reason not to, and to advise the person to avoid exercise until the assessment is complete. The NHS notes that a portable ECG is usually worn for 24 to 48 hours but can be worn for up to 7 days.

If a heart rhythm cause is suspected, NICE recommends ambulatory ECG monitoring, and says a tilt test should not be offered as the first-line investigation. The type of monitor depends on how often blackouts happen:

Treatment depends on the rhythm problem found. The NHS says how a heart rhythm problem is treated depends on the type and what is causing it, and that many people need no treatment or only regular check-ups. Options it lists include:

• Medicines to control the rate and rhythm of the heartbeat, such as beta blockers.

• Ablation, which burns or freezes the section of heart causing the faulty rhythm.

• Cardioversion, using electrical signals to reset the rhythm.

• A small electronic device such as a pacemaker, fitted under the skin to monitor and correct the rhythm.

You may also need treatment for an underlying condition. The NHS lists high blood pressure, coronary heart disease, heart valve disease, heart attack and Wolff-Parkinson-White syndrome among conditions that can cause heart rhythm problems. It also says an abnormal heartbeat can come from medicines, viruses, caffeine, alcohol, smoking or drugs, so identifying and addressing the trigger is part of the plan.

NICE advises that anyone who has had a blackout must not drive while waiting for specialist assessment, and that after assessment the clinician will explain your obligations to report it to the DVLA. The NHS says you must tell the DVLA if you are fainting regularly, and must not drive if your GP has referred you to a specialist and you are waiting to be assessed.

NICE also asks clinicians to discuss any implications for health and safety at work. If your job involves driving, heights or machinery, tell your employer's occupational health team or your doctor so the right adjustments can be made while the cause is established.

If you feel as though you are about to faint, the NHS suggests lying down with your legs raised, or sitting with your head between your knees, drinking water, crossing your legs while standing, rocking on your toes or clenching your fists.

On the NHS, a GP will usually arrange an ECG and, if there are red flags, refer you for urgent specialist cardiovascular assessment. Heart monitors and ambulatory ECG are provided through NHS cardiology services. Private cardiology clinics in the UK can also offer ECGs, monitoring and specialist review, but anyone who has fainted during exercise, has chest pain, or has a heart palpitation with a faint should be assessed urgently through emergency services rather than waiting for an appointment.