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Presyncope and Syncope
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Syncope is a sudden, transient loss of consciousness associated with inability to maintain postural tone and
with spontaneous recovery. Presyncope: premonition of syncope without the loss of consciousness
Epidemiology: 3% of patient each year and 1% get admitted
a. The elderly population has the highest incidence and is at increased risk for morbidity from syncopal
episodes. Aging causes blood vessel to become calcified and less compliant, leading to decrease flow
rates (S4 sound) Left ventricle becomes less compliant, resulting in increased diastolic filling pressures
and dependence on atrial kick”. There is a general decrease in adrenergic receptor responsiveness of
both the heart and the peripheral blood vessels. Chronic pathological processes contribute to decrease
cerebral perfusion: atherosclerosis, DM, HTN, valvular heart disease, medication
b. Pregnancy is associated with numerous physiologic changes including increased HR, decreased
peripheral resistance, and increased stroke volume.
i. Late pregnancy, uterus becomes very large and compresses the inferior vena cava when they lay
on the right or supine and have syncope. Any cardiac dysrhythmia can cause syncope
ii. Premature ventricular contractions are higher in women and cause syncope
Pathophysiology and etiology
a. The final common pathway of syncope is a lack of vital nutrient delivery to the brainstem reticular
activating system, leading to loss of consciousness and postural tone. Most commonly an inciting
event causes a drop in cardiac output, which, unless corrected rapidly, decreases oxygen and substrate
delivery to the brain. Less commonly, vasospasm or other alterations in flow singularly reduce CNS
blood flow.
b. The reclined posture of syncope and response of autonomic autoregulatory centers reestablish
cerebral perfusion, leading to a spontaneous return of consciousness. (When you syncopize, you fall
then return back
c. The most common causes are:
i. Orthostatic hypotension
ii. Vasovagal (reflex mediated)
iii. Cardiac dysrhythmia
Reflex mediated: vasovagal, situational, cough, micturition, defecation, swallowing, pain, carotid
sinus hypersensitivity, orthostatic hypotension
a. Normally, physical or emotional stress leads to increased sympathetic outflow and subsequent increase
in HR, BP, and cardiac output. In reflex-mediated syncope, stimulus produces an abnormal autonomic
NS reflex. Most commonly, an initial increase in sympathetic outflow is inappropriately withdrawn and
replaced by increased vagal tone. Hypotension with or without bradycardia follows, leading to decreased
cerebral perfusion and syncope. Less commonly, stimulus leads directly to vagal hyperactivity and
symptoms.
b. Prodromal symptoms are varied: light headed, dizzy, sweating, nausea, blurred vision or loss of
vision from periphery in, feel hot
c. Vasovagal syncope is incited by a noxious stimulus (pain, fear) or a characteristic setting: vertical,
standing position and the attacks are aborted or resolve after reclining (blood perfuses to brain)
d. Vasovagal syncope is typically preceded by warning symptoms, which may last several minutes. This
diagnosis should not be made without the typical prodromal symptoms. Dx: upright tilt table testing
e. Carotid sinus hypersensitivity: carotid body, located at the carotid bifurcation, is a pressure-sensitive
organ. The stimulation of an abnormally sensitive carotid body by external pressure may lead to:
i. Most commonly, abnormal vagal response with bradycardia and asystole of greater than 3s
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ii. Less commonly, vasodepressor response leading to a decreased BP of >50mmHg
f. It is more common in: men, elderly, patients with hypertension, ischemic heart disease, certain
head/neck malignancies
g. Dx: Carotid sinus massage; unless it results in syncope or recurrence of prodromal symptoms and is
associated with an inciting event (shaving or turning of head), it cannot be definitely diagnosed. Can be
done at the bedside in the ED with continuous EKG and BP monitoring after informed consent has been
obtained. Each carotid body is separately massaged for 5 to 10s. The test is considered positive if
symptoms are reproduced in the presence of asystole greater than 3s or fall in systolic blood pressure of
>50mmHg. Contraindicated: presence of bruits (carotid stenosis), history of CVA or MI
h. Situational syncope: abnormal or hypersensitive autonomic reflex response to a specific physical
stimulus; may be a component of increased intracranial or intrathoracic pressure leading to decreased
cerebral perfusion. The physical stimulus may be associated with another underlying disease process:
swallowing- achalasia, esophageal stricture
1. Micturition- BPH, prostate cancer
2. Defecation- colon cancer, constipation
i. Orthostatic Syncope: When a person assumes an upright posture, blood is shifted to the lower part of
the body and cardiac output drops. In a healthy individual, the autonomic NS responds with an increase
in sympathetic output and a decrease in parasympathetic output, producing increase in heart rate and
peripheral vascular resistance.
i. If patient remains upright and response is not efficient, we get decreased cerebral perfusion
ii. Patient will not syncopize from orthostatic hypotension unless standing for more than 3 minutes
j. Definition: A fall in systolic BP of >20mmHg upon assuming the upright posture
i. Caution in diagnosing orthostatic syncope based on orthostatic BP measurements alone, 5-50%
of patients with other causes of syncope have orthostatic hypotension on physical exam.
ii. Consider autonomic dysfunction- failure of vasoconstriction during orthostatic stress due to
primary disease, neuropathy, medications, volume depletion (GI losses, bleeding, diuresis)
1. Causes- diabetes Insipidus, alcohol, DM-MC)
Cardiac: structural cardiopulmonary disease, valvular heart disease, cardiomyopathy, pulmonary
hypertension, pericardial disease, aortic dissection, pulmonary embolism, MI, dysrhythmias
a. Causes of cardiac syncope (heart can’t maintain adequate cardiac output to maintain cerebral perfusion)
are divided into two categories:
i. Dysrhythmias- very common
ii. Structured cardiopulmonary disease
b. Both brady- and tachydysrhythmias may lead to transient cerebral hypoperfusion- there is no absolute
high or low heart rate that will produce syncope. Symptoms depend on both the autonomic NS’s
ability to compensate for decrease in cardiac output and the degree of Cerebrovascular atherosclerotic
disease.
c. Dysrhythmias are most likely to occur in the setting of underlying structural heart disease, or primary
electrolyte imbalance.
i. Syncope from dysrhythmias is typically sudden, with prodromal symptoms, if any, lasting
less than 3s
d. Syncope caused by underlying structural cardiopulmonary disease often occurs in the setting of
physical exertion, but also may be seen in response to vasodilation from medication or heat. A decrease
in SVR is normally compensated by an increase in cardiac output is fixed, limiting compensation
e. Aortic stenosis should be excluded as a cause of syncope in the elderly. Classic presentation: Chest
pain, DOE, Syncope
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f. Hypertrophic cardiomyopathy is characterized by asymmetric left ventricular hypertrophy and occurs
most commonly in the young.
g. Pulmonary outflow obstruction may also lead to syncope.
i. 13% of patients with acute pulmonary embolism develop syncope
h. Follow-up testing for cardiac cause includes: echocardiogram, electrophysiological testing, cardiac
stress testing, Holter monitor, and event recorder
i. Patients in this category will often be admitted
Neurological: transient ischemic attack, CVA, subclavian steal syndrome, migraine headache
a. Cerebrovascular disorders are rarely the primary cause of syncope, but must be considered in any patient
with syncope and signs or symptoms indicating central nervous system pathology.
i. Brainstem ischemia may cause a decrease in blood flow to the reticular activating system,
leading to sudden brief episodes of loss of consciousness. These episodes are typically associated
with other signs and symptoms of posterior circulation ischemia: visual disturbances, tinnitus,
vertigo
1. Check for carotid bruits
ii. Subclavian steal syndrome is a rare cause of brainstem ischemia, characterized by an abnormal
narrowing of the subclavian artery proximal to the origin of the vertebral artery such that with
exercise of the ipsilateral arm, blood is shunted, or “stolen”, from the vertebrobasilar system to
the subclavian artery supplying the arm muscles
1. More common in the left arm- occurs during weight lifting
2. Physical exam would show diminished pulses and BP in affected arm and arm
claudication
b. Other causes of brainstem ischemia: Vertebrobasilar atherosclerotic disease, basilar artery migraines
c. Diagnostic work-up includes: CT scan brain, EEG, carotid Doppler
d. Drugs/medications: anti-hypertensives, B-blockers, cardiac glycosides, diuretics, anti-dysrhythmias,
anti-psychotics, anti-depressants, nitrates, alcohol, cocaine
Psychiatric: Psychiatric disorders are found in a modest percentage of patients with syncope; the most
frequent psychiatric diagnoses were: generalized anxiety disorder and major depressive disorder
a. Hyperventilation is a provocative maneuver in diagnosing panic disorder and generalized anxiety
disorders, and can lead to hypocarbia, cerebral vasoconstriction, and subsequent syncope
i. Presentation typically in a young female, with repeated episodes of syncope, multiple prodromal
symptoms, and a generally positive review of symptoms. A psychiatric cause for syncope should
be one of exclusion, assigned only after organic causes have been excluded.
ii. Patient must breath into a bag to reabsorb carbon dioxide
Miscellaneous: anemia, hypoglycemia
a. Diagnosis: Goal of evaluation is to identify those at increased risk for immediate decompensation as a
result of an underlying disease process and for future risk of serious morbidity or sudden death.
b. History:
i. Clinical history should be obtained from patient and any witness of the event. Emphasis should
be placed on events leading up to the LOC: including position, activity, environmental stimuli
(pain, heat, and bad news), duration, premonitory symptoms (vasovagal), symptoms after
recovery (seizures), and cardiopulmonary, neurological symptoms.
1. Symptoms associated with syncope that should raise concern of life-threatening
diagnosis: headache (brainstem ischemia, stroke), chest pain (MI, aortic dissection,
PE), AMS, abdominal/back pain (aortic aneurysm, ectopic pregnancy), any sudden
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event without warning and associated with exertion should increase suspicion of
cardiac dysrhythmia or structural disease
ii. Any prior history of syncope should also be documented, as patient who have recurrent syncope
with more than five episodes in 1 year are more likely to have vasovagal syncope or a psychiatric
diagnosis than dysrhythmia as the cause.
iii. Aggressive dieting, vomiting, laxatives may cause electrolyte disturbances
Differential:
a. Occasionally, underlying mechanisms that causes syncope may result in associated seizure (cerebral
hypoperfusion). History is very important in differentiating syncope from seizure. A classic aura or
postictal confusion and muscle pain indicate seizure while characteristic prodromal symptoms suggest
reflex-mediated syncope. Witness information of the event may also be useful. (shaking, head turning,
and abnormal posture)
b. Physical examination
i. Focus on cardiovascular and neurological systems
1. Subclavian steal, aortic dissection
ii. BP measurements should be taken in both arms
1. Orthostatic pressure
c. Electrocardiogram: should be evaluated of prior cardiopulmonary disease, acute ischemia,
dysrhythmia, and heart block, prolonged QT interval. Patient should be monitored for abnormal cardiac
activity until a cardiac origin has been reasonably excluded.
i. Studies fail to show any benefit from a CT, EEG, or lumbar puncture if the neurological exam is
without findings
d. Laboratory testing: Complete blood count (CBC), urine pregnancy test, electrolyte panel
e. Consults: neurological, psychological
f. Disposition: Discharge vs. admittance of a patient with syncope in the absence of a diagnosis is directed
by an assessment of subsequent risk of mortality for that patient.
i. Elderly patients or patients with neurological, heart, or lung disease should be admitted
ii. Young patients with no neurological history should not be admitted