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.
Causes
Table 1. Causes of Syncope
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Table
| Cause | Symptoms | Prognostic Implication | Approximate Incidence Rate, % |
|---|---|---|---|
| Cardiac | Variable | Moderate-to-severe | 20 |
| Reflex/orthostatic | Warmth, nausea, diaphoresis | Benign | 35 |
| Neurologic | Seizure, transient ischemic attack, focal | Moderate | 10 |
| Psychiatric | No injury | Benign | 2 |
| Cause | Symptoms | Prognostic Implication | Approximate Incidence Rate, % |
|---|---|---|---|
| Cardiac | Variable | Moderate-to-severe | 20 |
| Reflex/orthostatic | Warmth, nausea, diaphoresis | Benign | 35 |
| Neurologic | Seizure, transient ischemic attack, focal | Moderate | 10 |
| Psychiatric | No injury | Benign | 2 |
Note that no diagnosis is determined in a significant fraction of patients presenting with syncope. Cardiac causes of syncope can be divided further into those related to structural heart disease and those related to a dysrhythmia.
Table 2. Cardiac Causes of Syncope
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Table
| Structural | Dysrhythmia | |
|---|---|---|
| Bradycardia | Tachycardia | |
| Aortic stenosis | Sick sinus syndrome | Ventricular tachycardia (VT) |
| Hypertrophic cardiomyopathy | Atrioventricular (AV) block | Ventricular fibrillation |
| Pulmonary embolus | Drug-induced | Torsade de pointes VT |
| Pulmonary hypertension | Supraventricular tachycardia | |
| Acute myocardial infarction | Atrial fibrillation/flutter | |
| Tamponade | ||
| Aortic dissection | ||
| Structural | Dysrhythmia | |
|---|---|---|
| Bradycardia | Tachycardia | |
| Aortic stenosis | Sick sinus syndrome | Ventricular tachycardia (VT) |
| Hypertrophic cardiomyopathy | Atrioventricular (AV) block | Ventricular fibrillation |
| Pulmonary embolus | Drug-induced | Torsade de pointes VT |
| Pulmonary hypertension | Supraventricular tachycardia | |
| Acute myocardial infarction | Atrial fibrillation/flutter | |
| Tamponade | ||
| Aortic dissection | ||
More on Syncope |
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References
Brignole M, Alboni P, Benditt DG, et al. Guidelines on management (diagnosis and treatment) of syncope--update 2004. Europace. Nov 2004;6(6):467-537.
Cannom DS. A critical appraisal of indications for the implantable cardioverter defibrillator (ICD). Clin Cardiol. May 1992;15(5):369-72. [Medline].
Chen-Scarabelli C, Scarabelli TM. Neurocardiogenic syncope. BMJ. Aug 7 2004;329(7461):336-41.
Connolly SJ, Sheldon R, Roberts RS, Gent M. The North American Vasovagal Pacemaker Study (VPS). A randomized trial of permanent cardiac pacing for the prevention of vasovagal syncope. J Am Coll Cardiol. Jan 1999;33(1):16-20. [Medline].
Grubb BP, Kosinski DJ. Syncope resulting from autonomic insufficiency syndromes associated with orthostatic intolerance. Med Clin North Am. Mar 2001;85(2):457-72. [Medline].
Kapoor WN. Syncope. N Engl J Med. Dec 21 2000;343(25):1856-62. [Medline].
Kapoor WN. Current evaluation and management of syncope. Circulation. Sep 24 2002;106(13):1606-9.
Linzer M, Yang EH, Estes NA 3rd, et al. Diagnosing syncope. Part 1: Value of history, physical examination, and electrocardiography. Clinical Efficacy Assessment Project of the American College of Physicians. Ann Intern Med. Jun 15 1997;126(12):989-96. [Medline].
Linzer M, Yang EH, Estes NA 3rd, et al. Diagnosing syncope. Part 2: Unexplained syncope. Clinical Efficacy Assessment Project of the American College of Physicians. Ann Intern Med. Jul 1 1997;127(1):76-86. [Medline].
Soteriades ES, Evans JC, Larson MG. Incidence and prognosis of syncope. N Engl J Med. Sep 19 2002;347(12):878-85. [Medline].
Sutton R, Brignole M, Menozzi C, et al. Dual-chamber pacing in the treatment of neurally mediated tilt-positive cardioinhibitory syncope: pacemaker versus no therapy: a multicenter randomized study. The Vasovagal Syncope International Study (VASIS) Investigators. Circulation. Jul 18 2000;102(3):294-9. [Medline].
Further Reading
Keywords
syncope, loss of consciousness, loss of postural tone, decreased cerebral perfusion, brainstem hypoxia, carotid sinus pressure, coronary artery disease, nonischemic cardiomyopathy, non-ischemic cardiomyopathy, ventricular tachyarrhythmia, congenital long QT syndrome, Wolff-Parkinson-White syndrome, WPW syndrome, Brugada syndrome, hypertrophic cardiomyopathy, syncopal episode, blackout, dizzy spell, seizure, dizziness, aortic stenosis, pulmonary embolus, pulmonary hypertension, acute myocardial infarction, acute MI, tamponade, aortic dissection, atrial fibrillation, atrial flutter, supraventricular tachycardia, SVT, torsades de pointes, ventricular tachycardia, VT, ventricular fibrillation, AV block, atrioventricular block, A/V block, A-V block, sick sinus syndrome, implanted cardioverter/defibrillators, ICDs
