Vasovagal syncope

Vasovagal syncope (also vasodepressor syncope, neurally mediated syncope or neurocardiogenic syncope), a form of dysautonomia, is the most common cause of fainting ("syncope" in medical terminology). Although it is particularly common (both historically and stereotypically) among young women, it is seen across all ages and genders and in otherwise completely healthy people. It is triggered by a number of factors, including prolonged standing, alcohol, fatigue, hunger, and anxiety. more...

Vasovagal syncope is caused by low heart rate and blood pressure, leading to inadequate circulation. The reduced oxygen supply to the brain results in syncope, or temporary loss of consciousness. Individuals usually regain consciousness within a few minutes and their prognosis is good, although the syncope has a tendency to recur.

Features

Prior to losing consciousness, the individual usually experiences symptoms such as nausea, inability to hear properly, difficulty speaking, exhaustion, tightness in the throat and blurry vision. Sweatiness and dizziness are also very common. These symptoms may last anywhere from seconds to minutes. This is followed by an episode of fainting; the individual regains consciousness within seconds to minutes. It is uncommon for vasovagal syncope to occur while the individual is lying down (supine); it normally occurs while standing or sitting.

During the episode, the individual will be unresponsive, and the pulse and blood pressure will be low. In some cases the individual may react violently while unconscious, this may be due to a fear response and increased adrenaline. The reaction may have the appearance of a seizure. Upon regaining consciousness, the individual may appear flushed and feel generally lethargic. The heart rate may still be slow, although it soon returns to normal.

Diagnosis

In addition to vasovagal syncope, a number of other medical conditions may cause fainting. It is essential to perform a thorough history (interview of the patient) and physical examination. If there is no sign of other medical problems or causes of fainting, and the patient's description is consistent with or suggestive of vasovagal syncope, no diagnostic testing may be necessary. However, if the fainting is recurrent, a tilt table test is usually performed. In this test, the patient lies flat on a table and is then tilted upright so that blood pressure and heart rate may be observed and measured to identify any severe changes. This test is particularly effective in identifying patients suffering from sensitive nervous systems. Depending on the physician's level of suspicion, other tests, including an electrocardiogram, may be performed.

Pathophysiology

Vasovagal syncope is due to a disorder of autonomic control of the cardiovascular system. It commonly occurs in normal people of all ages. Precipitating factors include alcohol consumption, fatigue, pain, hunger, and prolonged standing. It can also be triggered by situations causing anxiety, such as having blood drawn, as well as by hot or crowded situations.

The initial responses appear to be venous pooling and increased activity of the sympathetic nervous system. This causes the heart to contract forcefully while relatively empty, triggering ventricular mechanoreceptors and vagal nerve fibers. This has the effect of reducing sympathetic activity while stimulating parasympathetic activity, resulting in bradycardia and vasodilation, followed by syncope.

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