Dizzy Spells / Blackouts

It is estimated that 30-50% of the population will experience a fainting episode or “black-out” at some stage during their lives.  Fainting occurs for a wide variety of reasons but the common denominator is usually a sudden drop in blood pressure, which leads in turn to a transient reduction in blood flow and oxygen supply to the brain.

Usually, but not always, the affected individual will be aware of lightheadedness or dizziness just prior to passing out and may also report that their vision darkened or hearing faded prior to losing consciousness.  Nausea, vomiting, sweating, and an awareness of a fast or forceful heartbeat may also be reported.

In true fainting, loss of consciousness is invariably associated with loss of muscle tone resulting in the patient slumping to the ground if standing up at the time.  Occasionally, mild jerking movements will occur as a consequence of the reduced amount of oxygen reaching the brain, and this phenomenon should not be confused with the seizure-like activity that is seen in association with epilepsy.  Upon falling to the ground, blood flow to the brain is usually quickly restored and the patient invariably recovers consciousness within a minute or two; though it will often seem as though they have been unconscious for much longer.

The entity of fainting is also known by the medical term “syncope” which comes from a Greek word, which literally means “to cut short.”

Fainting is so common that it is accepted by most people as “one of those things” and it is usually only after several episodes have occurred that patients will seek medical attention.

The most common type of faint is due to a reflex interaction between the cardiovascular and the nervous system, which has the final say over the heart’s actual rate and the degree of relaxation of the body’s blood vessels.

Perhaps the most familiar type of faint, made famous by Hollywood actresses in the black and white films from the 1940s and 50s, involves a brief episode of collapse triggered by strong emotion or pain.  The term “vasovagal” is often applied to this type of faint to underline the importance of the close relationship between the human body’s blood vessels and the nervous system.

In the majority of cases, a careful description of the circumstances prevailing at the time of the faint as well as a detailed account from any eye-witnesses – if present – will provide most of the information needed to make a reasonably accurate diagnosis.

Simple investigations, such as an electrocardiogram – or “ECG” – and a cardiac ultrasound – or “echo” – are often helpful in ruling out significant structural heart disease, in which case the condition will usually carry a good prognosis.  Special recordings of the brain’s electrical activity – an electroencephalogram or “EEG” – and brain scans are usually unhelpful.

Other forms of reflex fainting may occur as the result of sudden neck movement, urination and playing a wind instrument such as a trumpet!

Apart from the so-called “reflex” forms of fainting, patients may also faint as a consequence abnormally fast or slow heart rhythms, disorders of the hearts muscle or valve function and conditions which may be associated with nervous system compromise such as diabetes and Parkinson’s disease.

Last, but not least, it is sometimes the case that certain medications, prescribed for the purpose of treating common medical conditions, may result in unintentional reductions in blood pressure such that patients may feel dizzy almost to the point of fainting, upon suddenly standing up, a symptom sometimes referred to as a “grey-out.”

When patients seek medical attention as a consequence of recurrent black-outs, prompt professional evaluation is vital to exclude a cause which may be associated with some form of serious heart disease.  Fortunately such patients comprise a relatively small proportion of all those who suffer from recurrent fainting episodes, but they usually require further investigations and management.

In the presence of heart muscle and/or valve disease certain non-invasive investigations such as a 24 or 48-hour continuous ECG recording of the heart’s rate and rhythm, or a treadmill exercise test to assess a patient’s exercise capacity and to look for evidence of abnormal heart rhythms or a lack of oxygen to the heart muscle during exercise.

In some instances invasive investigations such as diagnostic cardiac catheterisation studies and/or a specialised study of the heart’s “electrics” – known as an “electrophysiological or EP study” – may be necessary to determine the nature of any underlying blood vessel, heart valve or electrical problems.

If no cause can be found and a patient’s fainting continues despite appropriate advice and simple therapeutic measures (see below) a special test designed to stress the cardiovascular-nervous system interaction, may be performed.  Known simply as a “head-up tilt test,” this investigation involves an initial or baseline phase of lying flat for 10 minutes on a purpose-built tilt-table which has a foot-board and safety straps.  After the baseline phase, the table is then tilted upright for 20-40 minutes whilst continuous recordings of heart rate and blood pressure are made.  In some cases, medication may be administered during the test in a effort to improve its accuracy.  If and when a patient faints during a their head-up tilt-test – something which will happen in more that half of patients so-tested – it is possible for the treating physician to glean valuable information about the precise nature of their patient’s black-out (ie was it due predominantly to a change in heart rate, a change in blood pressure or simultaneous changes in both heart rate and blood pressure).  In all cases, if a patient were to faint the table is promptly returned to the horizontal position whereupon consciousness is rapidly restored.

In other situations it may be considered necessary to implant a small ECG “loop-recorder” which will continuously look out for and record any abnormally fast or slow heart rhythms for periods of up to 18 months; such an automatic recording of the heart’s rate and rhythm at the time of any subsequent fainting episode is likely to help provide a diagnosis and thus facilitate the subsequent management of the patient’s condition.

The immediate treatment of a patient who faints should be to summon help and then to try and ensure that the person who has just fainted is protected from injury, as far as possible.  One should quickly establish if the person who fainted is breathing and has a pulse.  So long as this is the case, the fainter should be allowed to lie flat, preferably on his or her side.  Elevation of the legs may speed recovery but one should not make the common mistake of trying to raise the patient’s head as this will usually prolong or aggravate the fainting episode.

The specific management of patients who complain of recurrent faints may involve advice regarding the avoidance of situations which are likely to result in recurrence (eg travelling as a standing passenger in packed commuter train when the weather is warm), increased salt and water intake, the use of compression hosiery, drug therapy and in occasional cases the recommendation that a pacemaker be implanted.  Patients with fainting episodes found to be due to abnormally fast heart rhythms may benefit from key-hole techniques to get rid of or ablate the abnormal electrical circuit responsible for their heart rhythm disorder or, in other instances benefit from the implantation of a miniature heart defibrillator.  However, the vast majority of patients with recurrent fainting episodes will have the reflex, or vasovagal variety, of fainting in association with a normal heart and as such their prognosis will be very good.


London bridge hospital