The neurally mediated syncopal syndromes
encompass a number of apparently related disturbances of reflex cardiovascular control
characterized by transient inappropriate bradycardia and/or vasodilation of various
arterial and venous beds. Certain of these syndromes (e.g., carotid sinus syndrome,
postmicturition syncope) are encountered occasionally in clinical practice, whereas others
are quite rare (e.g., swallow syncope). On the other hand, vasovagal syncope occurs so
frequently, that as a group, the neurally mediated syncopal syndromes are among the most
important causes of syncope. The pathophysiology of the neurally mediated syncopal
syndromes is incompletely understood, but can be considered in terms of four basic
elements: (1) the afferent limb; (2) central nervous system (CNS) processing; (3) the
efferent limb; (4) feedback loops. The afferent limb consists of several peripheral and
CNS trigger sites and the associated connections to medullary cardiovascular centers. CNS
processing and efferent signals result in both bradycardia, which may be marked or
relative, and vasodilatation. Failure of baroreceptor feedback controls to prevent
hypotension is important in facilitating development of symptomatic hypotension. Head-up
tilt table testing has become the diagnostic technique of choice for clinically assessing
susceptibility to neurally mediated syncope, particularly of the vasovagal type. Most
studies suggest that such testing discriminates relatively well between symptomatic
patients and asymptomatic control subjects, of whom 10%-15% have a false-positive test
results. Sensitivity of tilt table testing is more difficult to evaluate because there is
no accepted diagnostic gold standard. However, sensitivity (measured against a classic
presentation) has been estimated to range from 32%-85%, with most reports favoring the
higher end of this range. Treatment strategies for neurally mediated syncope remain
controversial. Many single episodes do not warrant treatment unless physical injury has
occurred, or a high risk occupation or avocation is involved. Tilt test exposure alone may
prove beneficial in educating patients with recurrent syncope to recognize warning signs
of an imminent faint. Large controlled clinical studies have not been performed to test
the efficacy of pharmacological therapy (e.g., beta-adrenergic blockers, disopyramide,
serotonin reuptake blockers, vasoconstrictors) or pacing therapy. Such studies may be
difficult to undertake due to the variable frequency of spontaneous symptoms and apparent
long periods of remission. Nonetheless, many investigators and clinicians have come to
rely on these agents, and on tilt testing to guide treatment decisions. Studies employing
careful correlation of long-term clinical follow-up with results of early and perhaps
later repeat tilt studies are still needed.
When my office
lease expired at the end of 2004, I decided to turn it into a
"sabbatical" from my private practice. Many years ago, in my
grandfather's 89th year of life, he told me, "John, it is important
to smell the roses while you can still smell them." His life
gave living a very good reputation. It is also true that the
pursuit of that philosophy required my grandfather to to re-open his
assay office/ore market in Wickenburg, Arizona as a 75-year-old because
he had run a little short of retirement money. Thus, if blessed with his
luck and health, I'll be back.. --jjh
