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Neurocardiogenic Syncope
Syncope (fainting) is one of the most common medical ailments encountered in clinical practice. Although frequently thought of as a condition with a neurological origin, it’s actually a cardiovascular problem - as such, a neurologic work-up is seldom rewarding. The two main causes of syncope are cardiac arrhythmias and neurocardiogenic (vasovagal, vasodepressor) syndromes. In both of these conditions, blood circulation to the brain is reduced, resulting in temporary loss of consciousness.
Among the arrhythmias causing syncope, tachycardias (fast heartbeats), particularly those of ventricular origin, rather than bradycardias (slow heartbeats) are more often the culprits. In most patients with any evidence of previously known heart disease, it is likely that their syncope is related to a cardiac arrhythmia, usually VT. This is a serious matter because in patients with syncope due to VT, it’s common for SCD to occur within the ensuing year, this should be preventable if the cause of the syncope is found and managed. All cardiac arrhythmias can be effectively controlled if proper diagnosis is made with the help of cardiac electrophysiologic studies. In general, if a slow heart beat is the problem it can be treated with a pacemaker. If rapid beating is discovered, the treatment will vary depending on the nature of the fast rhythm.
Another common cause of syncope/presyncope is neurocardiogenic (vasovagal) syndrome. This condition, known by physicians as "neurally mediated hypotension", is also referred to as "the fainting reflex", "vasodepressor syncope", "vasovagal syncope", or "autonomic dysfunction". In this condition blood vessels tend to expand, which leads to pooling of blood in the lower parts of the body. As a result, less blood reaches the brain and this causes fainting. The usual stimulus for this action resides in the nerves of the heart-hence the term neurocardiogenic. A head-up tilt test can uncover the underlying cause of the fainting in this syndrome. Neurocardiogenic syncope is usually treated with medications that reduce the probability of cardiac nerves triggering the cycle that leads to lightheadedness, dizziness or fainting.
Together, arrhythmias and neurocardiogenic syndromes account for more than 75% of the cases of unexplained fainting spells-so it’s important that the initial diagnostic work-up be designed to investigate these possibilities.
When Does Neurocardiogenic Syncope Lead to Symptoms?
Neurocardiogenic syncope occurs in predisposed individuals in the following settings:
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after prolonged periods of quiet upright posture (such as standing in line)
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after being in a warm environment (such as in hot summer weather, a hot crowded room, a hot shower or bath)
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immediately after exercise
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after emotionally stressful events (having blood drawn, being scared or anxious)
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some individuals get symptoms soon after eating, when blood flow has shifted to the intestinal circulation during the process of digestion
We are all susceptible to fainting by activation of the vaso-vagal reflex that results in a lowered blood pressure, however, an individual’s susceptibility varies day to day based upon genetic make-up, dietary factors, psychological state, and triggers such as infection, dehydration, and alcohol intake.
Why Does an Upright Posture Trigger Neurocardiogenic Syncope?
When a normal individual stands up, gravity causes blood to pool in the legs, and return of blood to the heart is decreased. In order to compensate for this reduction, the body releases a surge of adrenaline (epinephrine). The heart beats faster and more forcefully, thereby pumping blood more efficiently to vital organs (especially the brain).
In an individual with neurocardiogenic syncope, the reduction of blood retu
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