What is Vasovagal Syncope (fainting / blackouts)

Vasovagal syncope (pronounced sin-cope-pee) is a term used to describe an episode of fainting due to a low blood pressure, or heart rate, or a combination of both these factors. This condition is very common, with nearly 1 in 2 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 dilatation and pooling of the blood vessels in the leg and gut, which lowers the blood pressure.

Patients usually feel unwell at this point with symptoms of lightheartedness, dizziness, queasiness, and may be nauseous and sick, 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 syncope 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.

Vasovagal Syncope Diagnosis

Your syncope specialist doctor will take a clinical history which could strongly suggest a diagnosis of 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.

Tilt table test data showing blood pressure (BP) in top trace, and heart rate (HR, bottom trace), during head up tilting which is performed at 5 minutes into the study (first vertical line on the trace).

No significant changes occur in BP or HR, and at 20 minutes into tilting, sublingual nitrate is given. Within 5 minutes of nitrate, the BP drops from 110/70 to 40/20, and the heart rate drops from 100 to 40bpm, and the patient loses consciousness/blacks out (dark vertical line).

This is a positive tilt test demonstrating a mixed pattern of collapse where both the BP and HR drop during tilting. This is known as the VASIS 1 (mixed form) of vasovagal syncope.