what causes a blackout?


Causes of Blackouts.

The most common cause of a blackout is called syncope, (“sin-co-pee”).

Syncope describes blacking out because of a sudden drop in blood flow to the brain.

Usually syncope is so-called “Reflex Syncope”.  This is the cause of fainting.  The blackout occurs because blood pressure suddenly drops and the brain is temporarily starved of oxygen and glucose.

Although a faint can cause accidental injury, it is not dangerous of itself, provided the patient can lie down flat.

Lying flat tends to restore blood flow to the brain, especially if the head is down and the feet are raised.

About half of us suffer a faint at some time during life.

Other Causes of Blackouts.

The other important causes of a blackout are epilepsy and a psychological cause.

Whereas 50% of us may faint, only about 0.7% have epilepsy, so that a blackout is much more likely to be due to a faint than an epileptic attack.

Is it a fit or is it a faint?

Whilst we can all usually recognise a simple faint, distinguishing between syncope and epilepsy can be very difficult.

A simple faint usually has a warning period when the patient feels hot, sweaty and sickly, and they go pale.  They often then collapse rather gracefully, and once down on the ground, recover quickly.

Our concept of a “seizure” is when a patient collapses abruptly with a blackout, there are abnormal movements of the face, arms and legs, there may be incontinence and tongue-biting, and they take longer to recover.

What is not widely appreciated is that such a “seizure” can occur frequently with syncope as well as with epilepsy.  However, in syncope the mechanism is lack of blood flow to the brain, and in epilepsy, despite normal blood flow, the brain cells have a fit.

Why is this important to you?

This is important to all sufferers of blackouts.  Doctors and other staff may rely on a eye-witness to an attack where the seizure would appear to be due to epilepsy, but the true diagnosis is syncope.  Subtle differences exist in the appearance and the circumstances of the seizure that can be of great help.  If doctors get it wrong, this can lead to a misdiagnosis of epilepsy.

Misdiagnosis of Epilepsy.

About 1% of the population have a diagnosis of epilepsy, but evidence suggests that 20-30% of adult patients, and 40% of children with epilepsy in the UK are wrongly diagnosed, and do not have epilepsy at all.  In 2007, a UK Parliamentary Group on Epilepsy published their report on epilepsy services in England.  They noted that “…..74,000 people without the condition in England alone have a diagnosis of epilepsy and are receiving treatment for it.”

If a patient suffering epilepsy has doubt about the diagnosis, then the possibility of syncope should be considered.

Some causes of syncope are not simple and unthreatening.  If syncope is due to a heart rhythm abnormality or a tight heart valve, then a patient could be at high risk.

While epilepsy is diagnosed and treated by neurologists, syncope should be treated by a cardiologist.  This raises concerns for patients about just how they should go about getting to see the right person.

Back to Contents

Assessment of Blackouts.

Assessment is best done by a multidisciplinary team, to avoid the problems above.

Elsewhere in this website, I describe the specialist nurse-lead, multidiciplinary Rapid Access Blackouts Triage Clinic at Manchester Royal Infirmary.  The aim of this clinic is:-

  1. Bullet    To assess whether patients are at significant risk

  1. Bullet    To diagnose and treat patients if possible

  1. Bullet    To direct them onward to the correct specialist for further assessment if needed

  1. Bullet    To avoid patients getting stuck in the wrong “care-pathway” or getting the wrong


High Costs.

Real opportunities exist for savings to invest, as the APPG report notes, “The Joint Epilepsy Council has shown how improvements in epilepsy care in England could realise savings…..when the economic cost or the cost in opportunities for people who could be in work but are not due to misdiagnosis or mistreatment. When those costs are included, the estimated total cost of misdiagnosis in England rises to £134 million a year.”


There is scope for large-scale medico-legal claims  “The side effects of some [epilepsy drugs] should not be underestimated….[including] major malformations in the offspring of mothers with epilepsy can be associated with use in early pregnancy. Given the high number of misdiagnosed epilepsy cases in England, the APPG can only conclude that as a result tens of thousands of people are enduring these side-effects from drugs they should not be taking in the first place.”

Public Health Hazards of Misdiagnosis.

This represents a major public health disaster, since up to 120,000 patients in the UK are therefore wrongly diagnosed.  Many of these will receive a “trial of therapy” with anticonvulsants.  This serves only to cement a misdiagnosis, since many blackouts are isolated, and even true epileptic seizures may occur only rarely in patients who have a relatively low seizure-threshold. Up to 70% of “first-fit” patients have syncope, usually due to fainting.  However, in practice many doctors are tempted to treat epilepsy after a first or second seizure.  This is because of the important implications of epilepsy for education, relationships, employment, driving, insurance and childbearing.  Such a rapid resort to medication is unnecessary, since studies have shown that immediate versus delayed treatment for epilepsy has no effect on prognosis, but may substantially affect lives. 

Epilepsy versus Syncope.

The EEG is not diagnostic of epilepsy, especially in the over 35s. Therefore a diagnosis of epilepsy, and alternatively, a diagnosis of syncope, depend on the quality of clinical assessment, supported by simple bedside tests, such as the 12-Lead ECG.

Cardiac Risks.

A small number of patients with a misdiagnosis of epilepsy have a life-threatening electrical disease of the heart, such as LongQT Syndrome, Brugada Syndrome and Wolff-Parkinson-White Syndrome.  These can be detected by an ordinary 12-Lead ECG, which should be done in ALL cases.

Sorting out the different blackouts.

All patients with a blackout should have a clinical evaluation and an ECG.  An ECG should never be ommitted.

What should I ask?

There are 6 “Red Flag” questions, which are given in the algorithm.  Patients with no “Red Flags” and a normal 12-Lead ECG can be reassured.  The 18-Week Blackouts Commissioning Pathway will include a triage level between first responders in primary care and A&E, and specialist referral.

What if it is just fainting?

After a faint, a patient should not drive for 3 months.  Recurrent fainting can be a problem, and often there is accompanying “low blood pressure”.  Such patients often don’t take enough salt.  This can be encouraged, and other treatment options include Midodrine, an α-agonist, and pacemaker treatment in selected patients who have asystole during their attacks.  When pacemaker treatment is guided by recording a spontaneous faint using a long-term implantable ECG loop recorder, patients do very well.