Dizzy spells and blackouts

Book your consultation to discuss blackouts with Dr Segal

Dizziness and blackouts

There are numerous causes of dizziness and blackouts and these may relate to problems with the heart, the blood pressure, the brain and nerves, the inner ear and disorders of blood components.

Dizziness and blackouts due to disorders of heart rhythm – principally slow or fast heartbeats – are typically characterized by a rapid onset of symptoms and then a rapid recovery. Differentiating between the various causes of a blackout can be difficult and may require investigation from a cardiologist, neurologist and ENT surgeon, amongst others. This article will focus on cardiac causes of dizziness and blackouts and in particular disorders of heart rhythm. The medical term for a sudden blackout is called syncope (pronounced sing-kuh-pee).

More information:

Normal heart rhythm

The normal heartbeat originates in the heart’s pacemaker, known as the sino-atrial node (or SA node). This is located at the top of the right atrium (see figure). Electricity then conducts through the right atrium and across to the left atrium. The electrical impulse conducts through the AV node and into the ventricles via specialized conduction tissue called the His-Purkinje system. This means that in a normal heartbeat, each impulse that originates in the SA node will travel to the ventricles causing the atria and then the ventricles to contract sequentially (and hence why we hear two noises when our hearts beat).


Bradycardia means slow heartbeat and can occur due to problems in the SA node, the AV node or the His-Purkinje system. Cells in the heart, like the rest of the body, tend to deteriorate with increasing age and this can result in slowing of the impulses that originate in the SA node, or slowing of electrical conduction through the AV node or His-Purkinje system. This can cause a slow pulse, tiredness, dizzy spells and even blackouts if the slowing is severe or there is a pause in impulses of a few seconds or more.

Disease of the AV node and His-Purkinje system leads to slowing of electrical conduction between the atria and ventricles. This can result in only one ventricular contraction for every 2 atrial contractions (known as 2 to 1 heart block), complete heart block (in which no electricity gets through the AV node at all and the chambers beat independently of each other) and any combination in between e.g. 3 to 1, 3 to 2, 4 to 3, 5 to 1 heart block etc.

Diagnosis of Bradycardia

Bradycardia can usually be easily diagnosed from measuring a slow pulse, recording an ECG or from wearing a cardiac monitor. If symptoms of dizziness or blackouts are rare, a small ECG recording device can be inserted under the skin for longer term monitoring. These devices are known as internal loop recorders and they automatically record heart rhythm when the heart rate is very slow or very fast but a patient can also activate the device to tell it when they have had symptoms. Placing an antenna over the skin interrogates the device and collects the recorded information. This can be performed in a pacemaker clinic, or via a special remote monitoring device that can be installed at a person’s home using a wireless 3G cellular phone network (see Remote Monitoring).

Treatment of Bradycardia

Once diagnosed, bradycardias which cause symptoms such as dizziness or blackouts are usually treated by implanting a pacemaker (see Pacemakers & ICDs). Pacemakers prevent the heart from going slower than their programmed rate. They usually do not prevent or treat fast heart rhythms. If you do not have symptoms then it may not be necessary to implant a pacemaker. Occasionally, patients who require a drug that causes slowing of your heart rate e.g. a beta-blocker in patients who have had a heart attack previously or have high blood pressure, may need a pacemaker to allow them to take this drug safely. Similarly, if you have episodes of a very slow heartbeat or your heart stops for long periods but doesn’t cause symptoms, you may still be offered a pacemaker for safety reasons.


Loss of consciousness can also occur when the heart goes too fast – a tachycardia. There are several different types of tachycardia, but the most important type which causes syncope are those from the bottom chambers of the heart (the ventricles), called ventricular tachycardia (VT), and ventricular fibrillation (VF).


Ventricular Arrhythmias

The commonest reason to develop these rhythms is if you have previously had a heart attack. This is because a heart attack results in a scar forming inside the heart. Electricity can then rotate around and through the scar and can initiate these rhythms. The difference between VT and VF is that VT is an organized, regular rhythm with a single circuit and VF is a totally chaotic rhythm. VF always results in cardiac arrest if it sustains, as the heart cannot pump blood when the ventricle fibrillates. VT can also result in cardiac arrest if it is fast enough, but when it is slower it results in palpitations and feeling unwell. If it is very slow, which is more common if you take anti-arrhythmic drugs, it may cause mild or no symptoms.

VT or VF can also occur with other types of heart disease, particularly if they cause impairment of heart function or heart failure. These include dilated cardiomyopathy, hypertrophic cardiomyopathy, myocarditis and sarcoid as well as the channelopathies such as long QT and Brugada Syndromes, in which heart function is usually normal.

There are also several types of VT which are known to occur in people with normal hearts, including in young people. These have a good prognosis and can usually be managed effectively with medication or ablation. These include right ventricular outflow tract VT (RVOT VT) and fascicular VT.

Diagnosis of Ventricular Arrhythmias

This is essentially performed in the same way as for diagnosing bradycardia or other types of tachycardia, using ECGs, cardiac monitors you wear for days or weeks and occasionally by implanting a small monitor under the skin.

Treatment of Ventricular Arrhythmias

There are several treatments available for managing ventricular arrhythmias (VT and VF) ranging from medication to procedures and surgery. This is principally dependent on how well the heart functions. If VT occurs in a normal heart, then this almost always has a good prognosis. If heart function is poor, particularly if the left ventricle is impaired (e.g. from a previous heart attack), then VT has a poor prognosis and medications alone are insufficient.

For people with VT and poor heart function, and for almost everyone who experiences VF (or cardiac arrest due to VT) and survives, implantation of a device known as a defibrillator is necessary. These devices can rapidly pace the heart to stop VT or can deliver a shock to the heart to try and restore a normal rhythm if VF occurs. Please see the section on Pacemakers and ICDs for further information.

Fainting & Vasovagal Syncope

One of the commonest causes for people to feel dizzy or collapse is due to fainting. A faint can occur in anybody and does not necessarily imply there is an underlying problem with the heart. Faints and dizzy spells occur if the heart does not speed up sufficiently in certain situations. Most of us have felt momentarily dizzy if we stand up too quickly. This is because it takes a second or two for the heart to speed up appropriately to pump enough blood when we stand.

As well as heart rate, it is also important blood pressure rises when we stand up. For blood pressure to rise, our blood vessels must constrict, which means the area inside the vessel where blood flows becomes narrower. If blood vessels do the opposite and dilate when we stand, blood pressure will fall and can cause dizziness or fainting. This is why a common reason for fainting is standing for too long on a hot day e.g. soldiers in on a parade ground or child standing in the playground, or just standing in a packed bus of train. The heat causes the blood vessels to dilate and if this is too severe, blood pressure falls and the person will faint.

For most of us fainting is rare or never happens, except under extreme circumstances. Some people, however, have a very low threshold for fainting and this can cause major disturbances to their lifestyle. This appears to be particularly common in young females, usually in their twenties, and particularly if they are thin. They often have low blood pressure at rest when they feel well, so it doesn’t have to fall very much to make them feel ill or faint.

The medical term for fainting is vasovagal syncope, and if you faint often you are said to have vasovagal syndrome. Other terms for this condition are neurally mediated syncope or reflex syncope. Essentially, there is a mis-communication between the brain and heart in this condition causing heart rates to fall and blood pressure to drop when they should both do the opposite. The brain communicates with the heart via nerves called the vagus nerve and the sympathetic chain. It is the vagus nerve which slows heart rate and makes blood vessels dilate, so if it is dominant over the sympathetic chain, it can cause people to faint too often.

The good news about fainting is that unless you are unlucky enough to injure yourself severely when you fall, you will not die from this condition. The not so good news is that the treatments available are not as good as one would like and there is no cure, although many people with this condition do ‘grow out of it’.

Diagnosis of Vasovagal Syndrome

Listening to the details of the event at a consultation helps to diagnose faints or vasovagal syndrome. If there are clear features yo suggest a faint then the diagnosis is easy. Sometimes it can be challenging to be sure on the history alone, as it can sometimes be difficult to differentiate it from other causes of blackouts such as problems with the heart’s conduction system, types of epilepsy or what is caused psychogenic syncope. Epilepsy is a rare brain condition causing fits affecting less than 1% of the population. Psychogenic syncope is a faint caused by extreme stress or anxiety and is relatively common.

It is very important to know that all types of syncope, whether due to fainting, a heart problem, epilepsy or other conditions can cause a person to have jerky limb movements. This tends to makes witnesses, carers and doctors think it is due to an epileptic fit, but this may not be true. It is estimated that up to 30% of adults diagnosed with epilepsy do not have the condition.

Fainting and syncope in elderly people can also occur and because of impaired reflexes, joint problems and weaker muscles, often results in a fall. Sometimes elderly people will not remember blacking out before falling, so it is important elderly people who fall are investigated for heart problems.

Clues to syncope being due to fainting

There are several features that suggest syncope is due to fainting, although this is not foolproof:

  1. Occurs after a long period of sitting or standing
  2. Occurs in hot environments (particularly cramped trains or buses)
  3. Occurs after eating a big meal
  4. Occurs after eating hold or cold food
  5. Occurs in stressful situations, e.g. giving a presentation at work
  6. Occurs when having blood taken
  7. Occurs when coughing, laughing or sneezing
  8. Occurs when passing urine, particularly at night

Other associated symptoms

Other associated symptoms suggestive of a faint include:

  1. Getting warning symptoms of dizziness
  2. Feeling cold and clammy
  3. Sweating before, after or both
  4. Feeling or being sick
  5. Feeling tired and washed out for at least 30 minutes after collapsing

Tilt table testing

In some people the diagnosis of the cause of syncope can prove very challenging. Some doctors like to arrange a test called a tilt-table test. The test enables measurement of your blood pressure, heart rate and ECG when you are lying and standing almost to an upright position. A positive test is indicated by a fall in heart rate or blood pressure with standing and this may be associated with you fainting, albeit briefly. Often you may also be given a drug called GTN, which is given as a spray under the tongue, which is known to lower blood pressure. It is thought this increases the chance of you fainting.

My own personal belief is that tilt-table testing is not a particularly useful diagnostic tool. Unfortunately, up to 25% of people who have never fainted will faint on a tilt-table test and a similar number who are known to faint, will not. This means the test has a low degree of what is called ‘specificity’ and ‘sensitivity’. In essence, I believe this test isn’t good enough to help doctors decide if symptoms are due to fainting or not and can often give patients a very confusing picture and reassure or discourage them inappropriately. It is also unpleasant to be made to faint!

Treatments for Vasovagal Syncope

The mainstay of treatments for vasovagal syncope include:

  1. Measures to take when getting warning symptoms
  2. Recognising and avoiding precipitants
  3. Modifications to diet
  4. Modifications to lifestyle

Measures to take when getting warning symptoms include lying down, squatting or placing your head between your legs immediately to prevent blacking out fully. The precipitants listed above should be avoided if possible. At least 2 litres of water/day should be drunk when the weather is hot, alcohol should be avoided and salt intake should be increased (and certainly not avoided). Drinking water on its own without salt is not usually helpful, as the water will not be retained. Foods that contain salt include crisps, sausages, olives and bacon. If you don’t like any of these or don’t like the taste of salt, you can take salt tablets instead or drink sports drinks, which contain salts and glucose in addition to water, especially on hot days or if you feel warning symptoms. Alternatives include powdered electrolytes, which can be dissolved in water.

Occasionally drinking water quickly can help raise blood pressure, even before it has been absorbed fully. It is also known that the stimulant effects of caffeine can help some people with fainting. However, it may also cause palpitations and a fast heart rate and can also lead to dehydration.

Things you can do to help prevent faints include getting up carefully from a sitting to a standing position, regular exercise, eating small meals or even wearing support stockings. If you have to stand for a long time, regularly standing on your tiptoes can help to increase blood pressure and heart rate. If sitting for long periods, flexing you calf muscles or making fists with your hands is an alternative.

Medications for Vasovagal Syncope

Various drugs have been used for this condition, unfortunately most without huge benefit for the majority of people. However, a few patients do notice improvement in their symptoms if they take a regular medication. Drugs that are tried include midodrone, hydralazine and beta-blockers with varying degrees of success. The former two drugs cause water retention which can be an unpleasant side-effect.


It seems logical that if you have a condition in which you faint and your heart rate is too slow, fitting a pacemaker would help. This is because the pacemaker would prevent your heart from dropping below the programmed level.

There has been a lot of research into the use of pacemakers for people with vasovagal syndrome but unfortunately, the vast majority of studies have shown no improvement with pacemakers. This is because although heart rate doesn’t fall, the blood pressure does and fainting still occurs. One recent study suggests that a few people with frequent faints may still benefit from pacing. People who faint and have a long pause in between heart beats may be less likely to faint once a pacemaker is fitted, but this is certainly not completely proven and is likely only to help a small subset of patients.

For further information on fainting and vasovagal syncope, please visit the STARS charity website.

Other causes of loss of consciousness

Rapid heart rhythms that originate from the top or bottom chambers of the heart, can also sometimes cause fainting, although it is more common if the arrhythmia arises from the bottom chambers (the ventricles). Please see separate sections on SVT and Pacemakers and ICDs.
Heart Condition Oliver Segal Heart Condition Oliver Segal
For information and insights into heart conditions and treatments
Dr Oliver Segal - photo Dr Oliver Segal - photo
Find out more about Dr Oliver Segal
The Harley Stteet Clinic - hospital The Harley Stteet Clinic - hospital
Contact Dr Segal to book an appointment
back to top