During vasovagal syncope, profound bradycardia
and hypotension occur. Atropine administration can prevent the bradycardia but not the
hypotension, suggesting that marked peripheral vasodilation is a major cause of the fall
in arterial pressure. This concept has been confirmed since vasovagal syncope can be seen
in patients who have undergone heart transplantation and also in patients subject to
cardiac pacing. In both cases, there is no bradycardia but hypotension during the syncopal
attacks. The major site of the vasodilation is in skeletal muscle and muscle sympathetic
nerve activity is suppressed just prior to and during vasovagal attacks, indicating that
sympathetic withdrawal contributes to the dilation. However, the skeletal muscle
vasodilation seen during syncope is greater than that caused by sympathetic withdrawal
alone, and it is absent in limbs that have undergone surgical sympathectomy, or local
anesthetic nerve block. These observations suggest a role for neurally mediated
"active" vasodilation during syncope. The afferent neural pathways that evoke
the profound vasodilation during vasovagal attacks remain the subject of debate. The
neural pathways responsible for the active component of the dilation are also unknown.
Recent evidence has demonstrated that cholinergic, beta-adrenergic, and nitroxidergic
(nitric oxide) vasodilator mechanisms are not essential to observe the dilation,
demonstrating that the mechanisms responsible for it remain a continuing conundrum.
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
