Blackouts explained

A “blackout” describes a transient loss of consciousness and is a dramatic and frightening experience. Professor Richard Schilling gives us more detail about what can cause blackouts, and what they might be a sign of.

How do I know if it’s a cause for concern?

In this article I will discuss:

  • the signs that you need to look out for
  • the ways that your cardiologist at OneWelbeck Heart Health will investigate whether this is a sign of a serious problem
  • the treatment options

Is it a dangerous problem?

There are two reasons why people might lose consciousness:

  1. A brain problemepilepsy will usually result in fairly distinct symptoms. Patients will often have “aura” – strange sensations or smells immediately before hand, their loss of consciousness may be associated with signs like shaking, tongue biting and they will often be drowsy or confused afterwards for a short while.
  2. A drop in blood pressure – A drop in blood pressure to the brain can be caused by a number of things but the two most likely things that cause a blackout are either a faint (vasovagal syncope) or a heart rhythm problem.

Some blackouts can be safe

Faints are common, not associated with dangerous medical problems and have a number of typical features:

  • They are always associated with the patient being upright because the arteries in the legs dilate and gravity pulls blood away from the brain. This can’t happen if the patient is lying down.
  • There is often a trigger or promoter – pain, standing in a crowded hot train, dehydration.
  • There are often preceding symptoms – feeling cold, clammy, sweaty.
  • The symptoms resolve if you lie down and your legs are elevated (which moves the blood back to the brain).
  • Symptoms take some time to resolve and may recur if you stand up too quickly.

Blackouts that might be serious

Heart rhythm problems can cause faints because the heart no longer pumps effectively and the blood pressure drops. The features to look out for are:

  • They can happen at any time, whether you are standing sitting or lying.
  • There is no trigger, it can happen without any obvious cause.
  • There are no preceding symptoms – if patients are standing they may be unconscious before they hit the ground and will not put their hands out to save themselves and so may get head or facial injuries.
  • If/when you recover consciousness the symptoms resolve very quickly – patients will often say that they feel fine after and may even find it hard to believe that lost consciousness.

Apart from the character of the blackout there are two other important features that cardiologists look for that alert us that there may be a problem:

  • Is there a history of sudden unexplained death or blackouts in close relatives?
  • Do you have other heart disease or are you on heart medication?

How do cardiologists investigate blackouts?

The most important part of the investigation is the story. We will take a careful history to try and understand the nature of the blackout trying to distinguish between epilepsy, faints or heart rhythm blackouts using the features described above. The character of the story is important to determine what tests we do and how hard we look for the cause. A story very typical of a faint would prompt us to do a very basic set of tests. A more suspicious story would make us look harder.

Basic tests to look at risk

The single most important predictor of risk is whether the patient has an electrical or structural abnormality of the heart. In the absence of these the risk of a life-threatening heart rhythm problem is very low. Therefore the two basic tests we do are:

  • ECG (a recording of the electrical activation of the heart)
  • Echocardiogram (an ultrasound of the heart allowing us to look at the heart size, structure and function)


An ultrasound of the heart allowing visualisation of the pumping chamber and valves.

These tests are painless and risk free so we have a low threshold for suggesting these.

More sophisticated tests to look at risk

If there is any doubt about the basic tests or the story raises concerns then we may look at the heart in more detail with a cardiac MRI (magnetic resonance scan) or a CT scan to look at the coronary arteries that supply the heart with blood. These will tell us whether there is any evidence of scarring, or narrowing of the arteries.

Tests to confirm the diagnosis

Whatever the risk, it is often helpful to know what the cause of the blackout is because it will guide treatment, which in turn may have important implications for activities we normally take for granted like driving or swimming.

The key measurement that will tell us whether a blackout is caused by a rhythm problem is a recording of the ECG (i.e. the heart’s electrical rhythm) during a blackout event.

If blackouts are happening very frequently then this may be very straightforward by giving the patient a tiny ECG recorder that they can wear for a week or two which records the ECG continuously onto a memory card (aka 7/14 day ECG or Holter monitor).

Very often the blackouts are not happening that frequently, which makes recording more of a challenge. In this situation we may recommend a device called a loop recorder (or LINQ device)  which can be injected under the skin under local anaesthetic and will record the ECG on a continuous loop for 3-4 years. Therefore, if a blackout happens in that time the ECG will be captured and we will know whether this was a rhythm problem and exactly what rhythm problem it was.

The loop recorder

The loop recorder (right) is “injected” using the delivery tool (left) under local anaesthetic.

Treatments for blackouts

Clearly the treatment is dependent on the cause.

Slow heart rhythms causing blackouts will be treated with a device called a pacemaker. This is much more common in older people because the cause of the blackout is a slow heart rhythm caused by gradual wearing out of the hearts electrical system. The pacemaker is a computer and battery sealed in a can which is connected to the heart by a wire that is passed through a vein in the shoulder to the heart. The computer monitors the heart rhythm via the wire and if there is a pause, the pacemaker takes over seamlessly so the patient is never aware that there has been any change.

Pacemaker/defibrillator (left) that can be connected to the heart by wires (right-x-ray showing pacemaker wires in the heart)

Fast heart rhythms that cause blackouts, may be dangerous/life threatening. There are two approaches to treatment:

  1. Prevent the rhythm happening – by giving medication that slow or control the heart rhythm like betablockers. Alternatively it may sometimes be appropriate to find the source of the problem within the heart using a tiny wire passed up a puncture at the top of the leg. When the source is identified the catheter is placed on that source and energy applied to cauterise it, rendering it electrically inert and no longer able to support the abnormal rhythm. This procedure is called catheter ablation.
  2. Treat the rhythm and stop it killing the patient – for rhythms that are potentially life threatening it may also be prudent to give the patient the protection of an automatic implantable defibrillator. This is similar to a pacemaker but has the additional capability that it can deliver a shock to reset the heart and therefore automatically resuscitate them. Having a device like this is like having a paramedic with you all of the time.


Although most blackouts are not caused by a dangerous or life-threatening problem, they should always be reviewed with a doctor and most warrant some form of basic investigation to exclude dangerous causes. Even the most dangerous causes of blackouts can be treated and the patient protected from their life-threatening consequences. Cardiologists are very aware of this and will therefore always take a blackout seriously in order to avoid the tragedy of an avoidable, unnecessary sudden death.

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Here at OneWelbeck, we have a team of cardiology specialists, state of the art facilities and diagnostics, and highly competitive financial packages for self-funding patients as well as those with private health care.

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