Syncope

Introduction
Background

Syncope is defined as a transient self-limited loss of consciousness, usually leading to a fall. It is a subset of a broader range of conditions causing transient loss of consciousness. Syncope is a common medical problem accounting for up to 1% of emergency department visits and is the sixth leading cause of hospitalization for people older than 65 years.
Pathophysiology

Syncope results from a self-terminating inadequacy of global cerebral nutrient perfusion. In some patients, brainstem hypoxia triggers a posturing reflex that can appear like a seizure. A number of cardiac and noncardiac conditions can cause syncope (see Causes).

The most common type of syncope, neurocardiogenic syncope, is characterized by a sudden failure of the autonomic nervous system to maintain blood pressure to maintain cerebral perfusion.

Although the exact mechanism is not clear, one proposed mechanism is that in patients who are predisposed to have increased peripheral venous pooling, a sudden drop in preload results in a hypercontractile state. The forceful contraction stimulates mechanoreceptors, located primarily on the floor of the left ventricle. This mechanical activation results in neural traffic (falsely), mimicking hypertension and leading to sympathetic withdrawal and parasympathetic activation. The result is bradycardia (cardioinhibitory), vasodilatation (vasodepressor), or both (mixed response). Similar mechanoreceptors are also present in other parts of the body such as the bladder, rectum, esophagus, and lungs. Thus, other situational triggers to reflex syncope include micturition, defecation, deglutition, and cough.

As highlighted in a recent review by Hainsworth, "the trigger for the switch in autonomic response remains one of the unresolved mysteries in cardiovascular physiology."

Frequency
United States

Primary care physicians, cardiologists, and emergency department physicians frequently encounter patients with syncope. In the Framingham study, 822 (10.5%) of 7814 patients reported at least one syncopal event during the average follow up of 17 years. The incidence of new syncope was 6.2 per 1000 person-years. Assuming the constant incidence rate, a person living 70 years was estimated to have a 42% lifetime prevalence of syncope. The incidence rate is almost double in patients with cardiovascular disease compared with those without it.
Mortality/Morbidity

The prognostic significance of syncope depends on its cause (cardiac syncope with worse prognosis), the nature and severity of underlying structural heart disease, and the treatment initiated. Mortality is likely highest in patients with left ventricular dysfunction due to coronary artery disease or nonischemic cardiomyopathy. In these patients, syncope is frequently due to ventricular tachyarrhythmias. This risk is reduced substantially in patients treated with implanted cardioverter-defibrillators (ICDs). Even in patients with a benign cause of syncope, spells can result in significant injury, particularly in elderly persons.

In a recent study, mortality was about 30% higher among all participants with syncope than in those without syncope.
Race

No effect of race on the incidence of syncope is known.
Sex

Although earlier studies reported a slightly higher incidence of syncope in women compared with men, recent studies show similar incidence. A 72 per 1000 person-year incidence was noted in both men and women in a recent study based on the Framingham cohort.
Age

The incidence of syncope increases with age. Syncope is not uncommon in younger patients; neurally mediated (ie, neurocardiogenic) syncope accounts for most cases in younger patients. Occasionally, syncope in young patients presages a potentially life-threatening problem such as congenital long QT syndrome, Wolff-Parkinson-White (WPW) syndrome, Brugada syndrome, or hypertrophic cardiomyopathy.
Clinical
History

Patients with syncope may present with various complaints.

Patients may describe a syncopal episode in many ways, including blackout, dizzy spell, and seizure. Unexplained falls, particularly in elderly persons, also may be due to syncope.
Associated symptoms include palpitations, lightheadedness, diaphoresis, nausea and vomiting, warmth, chest pain, and shortness of breath.
Any history of focal neurologic symptoms or incontinence of bowel or bladder should also be sought.
Differentiating syncope from vertigo, in which a sensation of movement of either the patient or the surroundings transpires, is important. Vertigo usually reflects a neurologic or otolaryngologic problem.
Reports of eyewitnesses may be very helpful.
Triggers for the spells and a careful medication history, including over-the-counter and illicit drugs, should be sought.
The family history, particularly any family history of sudden death or syncope, should be reviewed, ie, the entire history is necessary.
The following clues suggest a higher risk of syncope and indicate that an expedient evaluation may be necessary:
Underlying structural heart disease, especially left ventricular dysfunction
Exertional syncope
Family history of sudden death
Significant traumatic injury due to loss of consciousness

Physical

A thorough physical examination should be performed on all patients who present with syncope.

Orthostatic vital signs at 1 and 3 minutes should be recorded.
The physician should look carefully for any cardiovascular or focal neurologic abnormalities.
Carotid sinus massage should be carefully performed during cardiac monitoring as long as carotid bruits or known carotid artery disease is not present.

http://emedicine.medscape.com/article/162110-overview