Vasovagal syncope (also vasodepressor syncope or neurocardiogenic syncope) 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. 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, 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. 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.
This mechanism is probably not the only explanation. Some inciting factors, such as hunger or anxiety, do not involve venous pooling. Also, patients with transplanted hearts (which are not innervated) also exhibit vasovagal syncope–like episodes.
The prognosis is usually good, although prolonged hypotension or asystole may cause damage. In addition, if syncope occurs without warning, injury may occur as a result of falling. Vasovagal syncope is often recurrent and may require treatment.
Treatment
Treatment for vasovagal syncope focuses on restoring blood flow during an episode and on prevention of future episodes.
Patients should be educated on how to respond to further episodes of syncope, especially if they experience warning signs (a "prodrome"). They should lie down or at least lower their head to increase blood flow to the brain. If the individual has lost consciousness, he should be laid down with his head turned to the side. Tight clothing should be loosened, to improve blood flow to the heart and brain. If the inciting factor is known, it should be removed if possible (for instance, the cause of pain).
The primary method of prevention is lifestyle modification: the patient should attempt to avoid situations known to cause syncope. Before known triggering events, the patient may increase consumption of salt and fluids to increase blood volume.
Beta blockers (ß-adrenergic antagonists) are the most common medication given. They work by lessening the sudden increase in the force with which the heart pumps (myocardial contractility). Other medications include disopyramide, paroxetine (Paxil), transdermal scopolamine, and midodrine.
For repeated episodes of vasovagal syncope or those that cause the heart to stop for a long time (prolonged asystole), a pacemaker may need to be implanted. The pacemaker monitors the heartbeat and will trigger a heartbeat if too long an interval passes between beats.
References
- Daroff, Robert B. & Carlson, Mark D. (2001). Faintness, Syncope, Dizziness, and Vertigo. In Eugene Braunwald, Anthony S. Fauci, Dennis L. Kasper, Stephen L. Hauser, Dan L. Longo, & J. Larry Jameson (Eds.), Harrison's Principles of Internal Medicine (15th Edition), pp. 111–115. New York: McGraw-Hill
Last updated: 05-08-2005 04:35:10
