All about vasovagal syncope: fainting explained

Written by: Dr Boon Lim
Published: | Updated: 20/02/2020
Edited by: Top Doctors®

Vasovagal syncope (pronounced sin-cope-pee) is a term used to describe an episode of fainting due to low blood pressure, low heart rate, or a combination of both. The condition is very common with 1 in 3 individuals experiencing syncope at some stage in their life.

Syncope usually occurs when the nervous system that controls the heart rate and blood pressure (the autonomic nervous system) starts to malfunction transiently in response to a trigger. This usually causes a slowing of the heart beat, and dilation and pooling of the blood vessels in the leg and gut, which lowers blood pressure. Patients usually feel unwell at this point with symptoms of lightheadedness, dizziness, queasiness, and may feel nauseous, sweaty and clammy, before passing out. These symptoms may be relieved on occasion by sitting down quickly or lying down and keeping the feet elevated. Typically, a patient who has a tendency to faint experiences a whole combination of factors which creates the ideal environment for syncope. Common triggers include:

• Standing for long periods (which increases pooling of blood in the legs)

• Heat exposure

• Large meals, particularly with alcohol

• Having blood taken, or the sight of blood

• Extreme fear, stress or anxiety

• Pain

• Standing up rapidly from a squatting or lying position

Diagnosing vasovagal syncope

Your doctor will take a clinical history which could strongly suggest a diagnosis of vasovagal syncope. If in doubt, further tests can be undertaken to rule out other causes of loss of consciousness, including an ECG, 24 hour ECG recording (Holter monitor), exercise testing, and an echocardiogram to look at the structure and pump function of the heart. You may also be referred for a tilt table test which can confirm the diagnosis of vasovagal syncope. During the tilt test, you are asked to lie down on a tilting table in the supine (flat) position, before being tilted upright at 60 degrees, to enhance venous pooling in the feet, which may then provoke a vasovagal syncope episode. Importantly, during the test, the blood pressure and heart rate are continuously monitored allowing us to observe any change in these readings corresponding to symptoms.

Management of syncope

Typically, the following simple management strategies are useful in preventing or minimising episodes of syncope.

• Hydration with plenty of fluids (at least 3L a day)

• Recognise warning symptoms (such as dizziness and nausea) and act on these by sitting or lying down

• Performing isometric exercises such as teeth and buttock clenching and tensing of the leg muscles, including quadriceps and calves, to improve blood flow back into the heart (think of it as “squeezing” blood that is pooling in the legs, back up into the heart and brain)

• Taking more salt (but ensure you have a normal blood pressure reading before you do this)

I think I have vasovagal syncope: Who do I see?

Vasovagal syncope can usually be diagnosed on the basis of a good clinical history. You should choose a top cardiologist who has experience in diagnosing and treating vasovagal syncope, and who can exclude other potential causes of loss of consciousness/blackouts.

By Dr Boon Lim

Dr Boon Lim is one of London's leading cardiologists and electrophysiologists. He specialises in heart rhythm disturbances, pacing and syncope at Imperial College and at his Harley Street clinic. He leads the established Imperial Syncope Diagnostic Service at Hammersmith Hospital and is frequently invited to national and international meetings to share his experience. He has a special interest in the mapping and ablation of atrial fibrillation (AF) and is highly-skilled at using modern 3-D mapping technologies.

Dr Lim has been awarded the prestigious Top Doctors Award in each of it's editions in 2017, 2018, and 2019-20. The Top Doctors Awards are peer-nominated by other medical specialists of the doctors that they would recommend to friends and family in times of medical need.

Dr Lim was awarded several distinguished prizes during his medical training at Cambridge University where he obtained a double First Class Honours Degree. He has continued his passion for education and research serving as an Honorary Senior Lecturer at Imperial College where he supervises several PhD students. He is very actively engaged in all aspects of research with a particular interest in developing the best techniques for treating atrial fibrillation. He is invited to speak both nationally and internationally to discuss his findings and to teach other physicians about the best techniques for complex mapping and ablation of atrial fibrillation and other complex arrhythmias.

He leads a very active syncope research team based at the Imperial Syncope Diagnostic Unit and is looking to improve healthcare delivery for patients through use of effective online education to help improve the quality of life for patients across the UK. 

Dr Lim is the author of the Penguin Life Experts book 'Keeping Your Heart Healthy' published in September 2021.

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