Syncope

Syncope is a short-term loss of consciousness and loss of postural stability followed by spontaneous return of consciousness to the previous neurologic baseline without the need for resuscitation. The condition is caused by transient interruption of cerebral blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure that may be benign or related to a underlying life-threatening condition. Syncope is not a distinct disease entity; rather, it is a symptom of another pathologic process, whether it be transient or a more established disease process. Syncope may be accompanied by other symptoms, such as light-headedness, sweating, palpitations, nausea, feeling warm or cold, and visual blurring. Workup includes a detailed history and physical examination, electrocardiography Electrocardiography Recording of the moment-to-moment electromotive forces of the heart as projected onto various sites on the body's surface, delineated as a scalar function of time. The recording is monitored by a tracing on slow moving chart paper or by observing it on a cardioscope, which is a cathode ray tube display. Normal Electrocardiogram (ECG), echocardiography, provocative testing (tilt-table test), or imaging of the suspected culprit vasculature. In many cases, a definite etiology is not found. Management is based on the underlying cause and can include physical countermaneuvers, stopping offending drugs, volume resuscitation, blood transfusion, and/or cardiac or vascular interventions.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Definition and Epidemiology

Definition

Syncope is a self-limiting, transient loss of consciousness caused by inadequate cerebral blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure that results in inadequate cerebral perfusion. 

  • There is associated loss of postural integrity. 
  • A spontaneous return to baseline levels of neurologic function without the need for resuscitation or intervention is typical.

Presyncope (also known as near-syncope) is part of the syncope spectrum.

  • Like syncope, it may present with prodromal symptoms. 
  • However, there is no loss of consciousness.

Epidemiology

  • Accounts for: 
    • > 2% of all ED encounters
    • > 5% of all hospital admissions
  • Lifetime prevalence in general population: approximately 10%–20%
  • Occurrence has a bimodal age distribution:
    • A peak in late adolescence to early adulthood (mostly vasovagal origin)
    • Second peak in older age, with a sharp rise thereafter

Etiology

Regardless of the underlying cause, syncope is a manifestation of hypoperfusion to either the cerebral cortex Cerebral cortex The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. Cerebral Cortex (bilateral) or the reticular activating system ( RAS RAS Renal artery stenosis (RAS) is the narrowing of one or both renal arteries, usually caused by atherosclerotic disease or by fibromuscular dysplasia. If the stenosis is severe enough, the stenosis causes decreased renal blood flow, which activates the renin-angiotensin-aldosterone system (RAAS) and leads to renovascular hypertension (RVH). Renal Artery Stenosis).

Neurocardiogenic syncope

  • Also known as vasovagal syncope
  • Neurocardiogenic symptoms most common cause of syncope
  • Usually a benign, self-limited episode of systemic hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension caused by a reflex that increases vagal tone and/or decreases sympathetic tone (i.e., excessive autonomic reflex activity)
  • Manifestations affecting perfusion include:
    • Vasodilation
    • Reduced cardiac filling 
    • Bradycardia
  • These dynamics result in: 
    • Cerebral hypoperfusion 
    • Loss of consciousness
    • Loss of cortical stimulation of postural tone
  • Situational causes (as a group, referred to as “situational syncope”) include:
    • Emotional stress:
      • Witnessing trauma
      • Sight of needles or blood
      • Extreme anxiety or panic attack
      • Extreme pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain 
    • Prolonged standing
    • Micturition
    • Defecation
    • Swallowing
    • Coughing/sneezing
    • Carotid hypersensitivity:
      • Syncope (or presyncope) resulting from excessive reflex response to carotid sinus stimulation
      • Stimuli include head turning, tight neckwear, shaving.

Orthostatic hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension

Orthostatic hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension is defined by a drop in systolic blood pressure ≥ 20 mm Hg  or reflex tachycardia > 20 beats per minute with positional change (i.e., failure or inadequacy of the autonomic reflex response).

Volume depletion Volume depletion Volume status is a balance between water and solutes, the majority of which is Na. Volume depletion refers to a loss of both water and Na, whereas dehydration refers only to a loss of water. Volume depletion can be caused by GI losses, renal losses, bleeding, poor oral Na intake, or third spacing of fluids. Volume Depletion and Dehydration:

  • Hemorrhage:
    • Traumatic hemorrhage
    • Retroperitoneal hemorrhage
    • GI blood loss
    • Splenic rupture Splenic rupture Splenic rupture is a medical emergency that carries a significant risk of hypovolemic shock and death. Injury to the spleen accounts for nearly half of all injuries to intra-abdominal organs. The most common reason for a rupture of the spleen is blunt abdominal trauma, specifically, motor vehicle accidents. Rupture of the Spleen
    • Obstetric/gynecologic blood loss
  • GI losses:
    • Vomiting
    • Diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
  • Diminished thirst drive (primarily in older individuals)
  • Water deprivation
  • Diuretic use
  • Immobility/deconditioning

Autonomic dysfunction:

  • Primary: 
    • Pure autonomic failure
    • Parkinson disease
    • Multiple system atrophy
    • Lewy body dementia
  • Secondary: 
    • Diabetes mellitus Diabetes mellitus Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and dysfunction of the regulation of glucose metabolism by insulin. Type 1 DM is diagnosed mostly in children and young adults as the result of autoimmune destruction of β cells in the pancreas and the resulting lack of insulin. Type 2 DM has a significant association with obesity and is characterized by insulin resistance. Diabetes Mellitus
    • Amyloidosis Amyloidosis Amyloidosis is a disease caused by abnormal extracellular tissue deposition of fibrils composed of various misfolded low-molecular-weight protein subunits. These proteins are frequently byproducts of other pathological processes (e.g., multiple myeloma). Amyloidosis
    • Spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord injury 
    • Autoimmune neuropathy
    • Paraneoplastic neuropathy

Cardiac syncope

  • Heart rhythm disturbances:
    • Tachyarrhythmias:
      • Supraventricular tachycardias
      • Ventricular tachycardias
    • Bradyarrhythmias Bradyarrhythmias Bradyarrhythmia is a rhythm in which the heart rate is less than 60/min. Bradyarrhythmia can be physiologic, without symptoms or hemodynamic change. Pathologic bradyarrhythmia results in reduced cardiac output and hemodynamic instability causing syncope, dizziness, or dyspnea. Bradyarrhythmias (with inadequate ventricular compensation): 
      • Sinus node dysfunction
      • Atrioventricular block Atrioventricular block Atrioventricular (AV) block is a bradyarrhythmia caused by delay, or interruption, in the electrical conduction between the atria and the ventricles. Atrioventricular block occurs due to either anatomic or functional impairment, and is classified into 3 types. Atrioventricular Block
    • Other:
      • Long QT syndrome Long QT syndrome Long QT syndrome (LQTS) is a disorder of ventricular myocardial repolarization that produces QT prolongation on electrocardiogram (ECG). Long QT syndrome is associated with an increased risk of developing life-threatening cardiac arrhythmias, specifically torsades de pointes. Long QT Syndrome
      • Brugada syndrome
      • Pacemaker failure
  • Myocardial ischemia:
    • MI MI MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction
    • Ischemic cardiomyopathy Cardiomyopathy Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). Overview of Cardiomyopathies
    • Left ventricular free wall rupture
  • Structural heart disease:
    • Hypertrophic cardiomyopathy Hypertrophic Cardiomyopathy Hypertrophic cardiomyopathy (HCM) is the most commonly inherited cardiomyopathy, which is characterized by an asymmetric increase in thickness (hypertrophy) of the left ventricular wall, diastolic dysfunction, and often left ventricular outflow tract obstruction. Hypertrophic Cardiomyopathy
    • Cardiac tamponade Cardiac tamponade Pericardial effusion is the accumulation of excess fluid in the pericardial space around the heart. The pericardium does not easily expand; thus, rapid fluid accumulation leads to increased pressure around the heart. The increase in pressure restricts cardiac filling, resulting in decreased cardiac output and cardiac tamponade. Pericardial Effusion and Cardiac Tamponade
    • Severe native valve disease:
      • Mitral valve stenosis
      • Aortic valve stenosis
      • Aortic insufficiency
    • Prosthetic valve dysfunction
    • Congenital coronary anomalies
    • Cardiac masses and tumors (e.g., atrial myxoma)

Syncope related to pathology of the great vessels

  • Pulmonary embolism Pulmonary Embolism Pulmonary embolism (PE) is a potentially fatal condition that occurs as a result of intraluminal obstruction of the main pulmonary artery or its branches. The causative factors include thrombi, air, amniotic fluid, and fat. In PE, gas exchange is impaired due to the decreased return of deoxygenated blood to the lungs. Pulmonary Embolism (PE; saddle embolus)
  • Severe pulmonary hypertension Pulmonary Hypertension Pulmonary hypertension (PH) or pulmonary arterial hypertension (PAH) is characterized by elevated pulmonary arterial pressure, which can lead to chronic progressive right heart failure. Pulmonary hypertension is grouped into 5 categories based on etiology, which include primary PAH, and PH due to cardiac disease, lung or hypoxic disease, chronic thromboembolic disease, and multifactorial or unclear etiologies. Pulmonary Hypertension
  • Aortic dissection Aortic dissection Aortic dissection occurs due to shearing stress from pulsatile pressure causing a tear in the tunica intima of the aortic wall. This tear allows blood to flow into the media, creating a "false lumen." Aortic dissection is most commonly caused by uncontrolled hypertension. Aortic Dissection

Cerebrovascular causes of syncope

  • Bilateral carotid artery disease
  • Subclavian steal syndrome Subclavian steal syndrome Subclavian steal syndrome occurs when narrowing/occlusion of the subclavian artery proximal to the origin of the vertebral artery causes a reversal of blood flow in the ipsilateral vertebral artery to continue perfusing the ipsilateral arm. The most common cause is atherosclerosis. Subclavian Steal Syndrome
  • Global cerebral hypoperfusion
  • Epidural hematoma (“lucid interval”)
  • Subarachnoid hemorrhage Subarachnoid Hemorrhage Subarachnoid hemorrhage (SAH) is a type of cerebrovascular accident (stroke) resulting from intracranial hemorrhage into the subarachnoid space between the arachnoid and the pia mater layers of the meninges surrounding the brain. Most SAHs originate from a saccular aneurysm in the circle of Willis but may also occur as a result of trauma, uncontrolled hypertension, vasculitis, anticoagulant use, or stimulant use. Subarachnoid Hemorrhage (SAH)
  • Transient ischemic attack Transient ischemic attack Transient ischemic attack (TIA) is a temporary episode of neurologic dysfunction caused by ischemia without infarction that resolves completely when blood supply is restored. Transient ischemic attack is a neurologic emergency that warrants urgent medical attention. Transient Ischemic Attack (TIA)

Medication-related syncope

Medication-related syncope is generally related to orthostasis or an effect on cardiovascular function.  

  • Diuretics (e.g., thiazides or loop diuretics Loop diuretics Loop diuretics are a group of diuretic medications primarily used to treat fluid overload in edematous conditions such as heart failure and cirrhosis. Loop diuretics also treat hypertension, but not as a 1st-line agent. Loop Diuretics):
    • May induce volume depletion
    • May induce electrolyte disturbances
  • Vasoactive medications (e.g., calcium channel blockers Calcium Channel Blockers Calcium channel blockers (CCBs) are a class of medications that inhibit voltage-dependent L-type calcium channels of cardiac and vascular smooth muscle cells. The inhibition of these channels produces vasodilation and myocardial depression. There are 2 major classes of CCBs: dihydropyridines and non-dihydropyridines. Class 4 Antiarrhythmic Drugs (Calcium Channel Blockers), beta blockers, alpha blockers, nitrates Nitrates Nitrates are a class of medications that cause systemic vasodilation (veins > arteries) by smooth muscle relaxation. Nitrates are primarily indicated for the treatment of angina, where preferential venodilation causes pooling of blood, decreased preload, and ultimately decreased myocardial O2 demand. Nitrates, etc.):
    • May induce vasodilation
    • May induce bradycardia or suppress vascular autoregulation
  • Antiarrhythmics:
    • May predispose to development of prolonged QT interval
    • Prolonged QT interval predisposes to torsade de pointes
  • Antidepressants (e.g., tricyclic drugs, selective serotonin reuptake inhibitors Serotonin Reuptake Inhibitors Antidepressants encompass several drug classes and are used to treat individuals with depression, anxiety, and psychiatric conditions, as well as those with chronic pain and symptoms of menopause. Antidepressants include selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), and many other drugs in a class of their own. Serotonin Reuptake Inhibitors and Similar Antidepressant Medications (SSRIs), etc.):
    • Indirect mechanism related to suppression of sympathetic neurotransmitters
    • May suppress vascular autoregulation

Toxic metabolic causes of syncope

  • Electrolyte disturbance
  • Hypoxia
  • Hypoglycemia Hypoglycemia Hypoglycemia is an emergency condition defined as a serum glucose level ≤ 70 mg/dL (≤ 3.9 mmol/L) in diabetic patients. In nondiabetic patients, there is no specific or defined limit for normal serum glucose levels, and hypoglycemia is defined mainly by its clinical features. Hypoglycemia
  • Intoxication:
    • Alcohol
    • Illicit drugs
    • Prescription medication abuse
Dynamics of neurocardiogenic syncope

Dynamics of neurocardiogenic (also known as vasovagal, reflex, or neurally mediated) syncope:
Normally, the heart and the CNS provide hemodynamic inputs to the brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem, which then balances sympathetic and parasympathetic tone to maintain perfusion.
A failure of this mechanism, in the face of physiologic stress, results in a paradoxical withdrawal of sympathetic tone simultaneous to increased parasympathetic discharge.
Vasodilation and relative hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension combined with bradycardia lead to poor cerebral perfusion and syncope.

Image by Lecturio.

Mnemonic

Causes of syncope “SVNCOPE”

  • Situational
  • Vasovagal
  • Neurogenic
  • Cardiac
  • Orthostatic hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension
  • Psychiatric
  • Everything else

Clinical Presentation

Presenting symptoms

  • Witnessed or unwitnessed loss of consciousness
    • May or may not be preceded by prodromal symptoms
    • May or may not be associated with an identifiable trigger associated with situational syncope
    • May or may not be attributed to an underlying pathologic disturbance
  • Loss of postural tone (e.g., a fall if standing, a slump if seated)
    • May or may not be accompanied by brief convulsive activity
      • May be mistaken for seizure
      • Distinguished from seizure by brevity of convulsions and absence of postictal state
    • Postural tone returns to normal after individual regains consciousness
  • Major or minor trauma associated with loss of postural tone
  • Spontaneous return of consciousness:
    • Individual may report fatigue or tiredness.
    • Generally, return to neurologic baseline level of function, unless:
      • Cause of syncope is cerebrovascular in nature.
      • Neurologic trauma is sustained during postural loss.

Prodromal symptoms

The following symptoms are associated with imminent syncope or presyncope:

  • Light-headedness
  • A feeling of being warm or cold
  • Sweating
  • Palpitations
  • Nausea or nonspecific abdominal discomfort
  • Visual blurring; can proceed to temporary darkening
  • Diminution of hearing and occurrence of unusual sounds
  • Pallor reported by onlookers

Red flags

Certain presentations suggest more serious causes of syncope:

  • Syncope during exertion
  • Syncope while supine
  • Multiple recurrences within a short period of time
  • Heart murmur or other findings suggesting structural abnormalities
  • Older age
  • Significant injury during syncope
  • Family history of: 
    • Sudden unexplained death
    • Exertional syncope
    • Unexplained recurrent syncope
    • Seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures

Diagnosis

The etiology of approximately ½ of syncope cases remains undetermined despite an exhaustive workup. It is imperative to rule out life-threatening etiologies, such as cardiac syncope, PE, subarachnoid hemorrhage, and blood loss.

History

  • Number, frequency, and duration of episodes
  • Onset
  • Position
  • Trauma sustained during loss of postural tone
  • Provocative factors:
    • During or immediately after exertion/exercise (red flag)
    • During or immediately after:
      • Micturition
      • Defecation
      • Coughing
      • Swallowing
    • While in a warm and/or crowded place
    • During prolonged standing
    • During the postprandial period
    • In association with:
      • Emotional stress
      • Fear
      • Intense pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain
    • Immediately following carotid sinus stimulation
    • While supine (suggestive of a serious problem)
  • Associated symptoms preceding and/or following the event:
    • Nausea
    • Vomiting
    • Feeling cold or clammy
    • Visual auras or blurry vision
    • Palpitations
    • Shortness of breath
    • Chest pain Chest Pain Chest pain is one of the most common and challenging complaints that may present in an inpatient and outpatient setting. The differential diagnosis of chest pain is large and includes cardiac, gastrointestinal, pulmonary, musculoskeletal, and psychiatric etiologies. Chest Pain
  • Additional symptoms following the syncopal event:
    • Confusion
    • Fatigue
    • Injury
    • Bladder or bowel incontinence
    • Recurrent syncope 
  • Witnessed signs:
    • Manner in which collapse happened
    • External appearance of individual
    • Estimated duration of loss of consciousness
    • Physical movements noted
    • Any breathing changes seen
    • Associated trauma
  • Preexisting medical conditions:
    • Structural heart disease:
      • Ischemic heart disease Ischemic heart disease Coronary heart disease (CHD), or ischemic heart disease, describes a situation in which an inadequate supply of blood to the myocardium exists due to a stenosis of the coronary arteries, typically from atherosclerosis. Coronary Heart Disease
      • Valvular heart disease
      • Congenital heart disease
      • Cardiomyopathies
      • Prior cardiac surgery Cardiac surgery Cardiac surgery is the surgical management of cardiac abnormalities and of the great vessels of the thorax. In general terms, surgical intervention of the heart is performed to directly restore adequate pump function, correct inherent structural issues, and reestablish proper blood supply via the coronary circulation. Cardiac Surgery
    • Neurologic conditions:
      • Seizure disorders
      • Migraine Migraine Migraine headache is a primary headache disorder and is among the most prevalent disorders in the world. Migraine is characterized by episodic, moderate to severe headaches that may be associated with increased sensitivity to light and sound, as well as nausea and/or vomiting. Migraine Headache headaches
      • Parkinson disease
      • Stroke
    • Diabetes mellitus Diabetes mellitus Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and dysfunction of the regulation of glucose metabolism by insulin. Type 1 DM is diagnosed mostly in children and young adults as the result of autoimmune destruction of β cells in the pancreas and the resulting lack of insulin. Type 2 DM has a significant association with obesity and is characterized by insulin resistance. Diabetes Mellitus:
      • Predisposition to cardiovascular/cerebrovascular disease
      • Prone to development of autonomic neuropathy
    • Intoxication:
      • Alcohol
      • Illicit drugs
      • Prescription narcotics (e.g., opioids Opioids Opiates are drugs that are derived from the sap of the opium poppy. Opiates have been used since antiquity for the relief of acute severe pain. Opioids are synthetic opiates with properties that are substantially similar to those of opiates. Opioid Analgesics, benzodiazepines Benzodiazepines Benzodiazepines work on the gamma-aminobutyric acid type A (GABAA) receptor to produce inhibitory effects on the CNS. Benzodiazepines do not mimic GABA, the main inhibitory neurotransmitter in humans, but instead potentiate GABA activity. Benzodiazepines, amphetamines)
  • Medications:
    • Diuretics
    • Antihypertensive agents 
    • Antiarrhythmic agents 
  • Family history:
    • Sudden death (< 40 years of age)
    • Familial cardiomyopathy Cardiomyopathy Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). Overview of Cardiomyopathies
    • Seizure disorders or migraine headaches
    • Familial predisposition to syncope

Physical examination

  • Vital signs:
    • Pulse and blood pressure taken with individual supine, seated, and standing (orthostatic vital signs)
      • Drop of systolic BP > 20 mm Hg diagnostic of orthostatic hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension
      • Drop of systolic BP > 30 mm Hg in hypertensive individuals
    • Note speed and regularity of pulse.
    • Note rate, regularity, and intensity of breathing effort.
  • Cardiac examination:
    • Note presence of heart murmur, especially if new or worsened.
    • Comparative pulse timing and blood pressure: 
      • Incongruence between upper limbs indicative of proximal aortic dissection
      • Incongruence between upper and lower limbs indicative of distal aortic dissection
    • Note presence of jugular venous distention (JVD), pulmonary rales, peripheral edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema.
    • Note presence of bruits, especially if new or worsened.
  • Neurologic examination:
    • Note cognitive status, presence of disorientation, or confusion.
    • Note level of consciousness, especially if deteriorating.
    • Note presence of focal neurologic deficit(s).

ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG)

ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) is indicated for all individuals presenting with syncope, regardless of suspected etiology. ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) monitoring should be continued throughout the ED or hospital stay. Notable findings may include:

  • Arrhythmias
  • ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) changes suggestive of cardiac ischemia
  • PR segment, QRS duration, QT interval prolongation (especially if new or worsened)
  • Right heart strain pattern (S1, Q3, T3) suggestive of PE
  • Conduction blocks
  • Specific signs of congenital or acquired structural heart disease

Echocardiography

  • Used to screen for structural heart disease in known or suspected cases
  • May detect:
    • Valvular abnormalities
    • Wall-motion abnormalities
    • Left ventricular dysfunction
    • Elevated pulmonary pressures (suggestive of PE)
    • Pericardial effusion Pericardial effusion Pericardial effusion is the accumulation of excess fluid in the pericardial space around the heart. The pericardium does not easily expand; thus, rapid fluid accumulation leads to increased pressure around the heart. The increase in pressure restricts cardiac filling, resulting in decreased cardiac output and cardiac tamponade. Pericardial Effusion and Cardiac Tamponade
    • Masses
    • Vegetations

Laboratory evaluation

  • CBC:
    • RBC indices for: 
      • Anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview
      • Blood loss
      • Erythrocytosis
    • WBC indices for: 
      • Evidence of infection
      • Lymphoproliferation
    • Platelet count for: 
      • Bleeding
      • Thrombotic tendencies
  • CMP to evaluate for:
    • Renal or hepatic dysfunction
    • Electrolyte disturbance
    • Acid–base imbalance
    • Hypoglycemia Hypoglycemia Hypoglycemia is an emergency condition defined as a serum glucose level ≤ 70 mg/dL (≤ 3.9 mmol/L) in diabetic patients. In nondiabetic patients, there is no specific or defined limit for normal serum glucose levels, and hypoglycemia is defined mainly by its clinical features. Hypoglycemia
  • Coagulation studies Coagulation studies Coagulation studies are a group of hematologic laboratory studies that reflect the function of blood vessels, platelets, and coagulation factors, which all interact with one another to achieve hemostasis. Coagulation studies are usually ordered to evaluate patients with bleeding or hypercoagulation disorders. Coagulation Studies:
    • PT/PTT to evaluate for coagulopathy
    • Especially in suspected intracerebral/cerebrovascular or GI hemorrhage
  • Cardiac biomarkers:
    • Includes:
      • MB isoenzyme of creatine kinase (CKMB)
      • Cardiac troponins
      • Beta-natriuretic peptide
    • Evaluate for the presence of ischemic heart disease and/or heart failure
  • Urine toxicology screen
  • Urine hCG for women of childbearing age

Imaging

  • Neuroimaging (CT, MRI of head/brain) for: 
    • Suspected intracranial mass
    • Intracranial hemorrhage
    • Cerebrovascular accident Cerebrovascular accident An ischemic stroke (also known as cerebrovascular accident) is an acute neurologic injury that occurs as a result of brain ischemia; this condition may be due to cerebral blood vessel occlusion by thrombosis or embolism, or rarely due to systemic hypoperfusion. Ischemic Stroke
    • Traumatic brain injury
  • CTA of the chest or ventilation/perfusion (VQ) scan for suspected PE
  • Carotid Doppler scan for suspected carotid vascular disease
  • Abdominal CT or ultrasonography to evaluate for: 
    • Splenic rupture Splenic rupture Splenic rupture is a medical emergency that carries a significant risk of hypovolemic shock and death. Injury to the spleen accounts for nearly half of all injuries to intra-abdominal organs. The most common reason for a rupture of the spleen is blunt abdominal trauma, specifically, motor vehicle accidents. Rupture of the Spleen
    • Aortic aneurysm Aneurysm An aneurysm is a bulging, weakened area of a blood vessel that causes an abnormal widening of its diameter > 1.5 times the size of the native vessel. Aneurysms occur more often in arteries than in veins and are at risk of dissection and rupture, which can be life-threatening. Extremity and Visceral Aneurysms
    • Intraabdominal and retroperitoneal bleeding
  • Abdominoplevic ultrasonography to evaluate for ectopic pregnancy Ectopic pregnancy Ectopic pregnancy refers to the implantation of a fertilized egg (embryo) outside the uterine cavity. The main cause is disruption of the normal anatomy of the fallopian tube. Ectopic Pregnancy or gynecologic sources of hemorrhage 
  • Lower-extremity ultrasonography to evaluate for deep vein thrombosis Deep vein thrombosis Deep vein thrombosis (DVT) usually occurs in the deep veins of the lower extremities. The affected veins include the femoral, popliteal, iliofemoral, and pelvic veins. Proximal DVT is more likely to cause a pulmonary embolism (PE) and is generally considered more serious. Deep Vein Thrombosis ( DVT DVT Deep vein thrombosis (DVT) usually occurs in the deep veins of the lower extremities. The affected veins include the femoral, popliteal, iliofemoral, and pelvic veins. Proximal DVT is more likely to cause a pulmonary embolism (PE) and is generally considered more serious. Deep Vein Thrombosis)
  • Specific imaging indicated for evaluation of other suspected etiologies

Other tests

  • Tilt-table test: changes in posture from lying to standing to evaluate cause of syncope
  • Electroencephalography to evaluate for possible seizure
  • Holter monitoring or loop recording for cardiac rhythm disturbances that manifest during the initial ED visit or hospital stay
  • Other specific testing indicated for evaluation of other suspected etiologies

Management

Much of the management of syncope will be specific to the confirmed or suspected etiology. Because the specific etiology of syncope often goes undiagnosed, general measures are discussed here.

Treatment of prodromal symptoms

This includes physical countermaneuvers, such as: 

  • Leg Leg The lower leg, or just "leg" in anatomical terms, is the part of the lower limb between the knee and the ankle joint. The bony structure is composed of the tibia and fibula bones, and the muscles of the leg are grouped into the anterior, lateral, and posterior compartments by extensions of fascia. Leg crossing: simultaneous tensing of leg, abdominal, and buttock muscles
  • Handgrip: consists of maximum grip on a rubber ball or similar object
  • Arm tensing: involves gripping one hand Hand The hand constitutes the distal part of the upper limb and provides the fine, precise movements needed in activities of daily living. It consists of 5 metacarpal bones and 14 phalanges, as well as numerous muscles innervated by the median and ulnar nerves. Hand with the other while simultaneously abducting both hands

Immediate treatment

  • Assist the individual to the ground, chair, or stretcher to avoid traumatic injury.
  • Lay individual supine with legs elevated to help with venous return to the heart and to eventually restore cerebral perfusion.
  • Assess vital signs (blood pressure, pulse, respiratory rate).
  • Observe other signs (pallor, diaphoresis, seizure activity).
  • Get additional assistance:
    • Call 911.
    • “Is there a doctor in the house?”
  • Attempt to arouse the individual.
  • If high-risk factors are present, admit to the most appropriate unit in the hospital (e.g., telemetry, ICU).

Risk assessment

  • Low risk for poor outcomes if no evidence of heart disease is identified
  • High-risk features associated with poor outcomes:
    • Evidence of structural or ischemic heart disease
    • History of structural or ischemic heart disease
    • Older age
    • Syncope while supine
    • Syncope during exertion
    • Palpitations at time of syncope
    • Chest pain Chest Pain Chest pain is one of the most common and challenging complaints that may present in an inpatient and outpatient setting. The differential diagnosis of chest pain is large and includes cardiac, gastrointestinal, pulmonary, musculoskeletal, and psychiatric etiologies. Chest Pain at time of syncope
    • Dyspnea at time of syncope
    • Syncope without prodrome
    • Family history of sudden cardiac death
    • Association with thunderclap headache
    • High-risk physical examination findings:
      • Abnormal vital signs
      • Abnormal cardiac exam
      • Abnormal pulmonary exam
      • Abnormal neurologic exam
    • Abnormal ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG)
    • Persistently low blood pressure
    • Low hematocrit
  • Promptly rule out life-threatening causes of syncope or syncope mimics (seizure and cerebrovascular accident are not true causes of syncope):
    • MI MI MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction
    • Nonperfusing cardiac arrhythmia
    • PE
    • Cerebrovascular accident Cerebrovascular accident An ischemic stroke (also known as cerebrovascular accident) is an acute neurologic injury that occurs as a result of brain ischemia; this condition may be due to cerebral blood vessel occlusion by thrombosis or embolism, or rarely due to systemic hypoperfusion. Ischemic Stroke
    • Intracranial hemorrhage
    • Aortic rupture
    • Massive hemorrhage
    • Seizure

Therapies to prevent syncope recurrence

Reflex syncope: carotid sinus syncope:

  • Reassurance and education about nature, risks, and prognosis
  • Avoid mechanical manipulation of the carotid sinuses (e.g., abrupt turning of the neck, wearing tight collars).
  • Vasodilators should be avoided or reduced where possible.
  • Medication:
    • Midodrine
    • Beta blockers
    • Paroxetine
    • Disopyramide 
  • Pacemakers (those with cardioinhibitory responses)

Orthostatic hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension

  • Medication-induced:
    • Discontinue offending medication.
    • Substitute with an alternative agent.
    • Adjust dose.
    • Change timing of drug administration.
  • Volume depletion Volume depletion Volume status is a balance between water and solutes, the majority of which is Na. Volume depletion refers to a loss of both water and Na, whereas dehydration refers only to a loss of water. Volume depletion can be caused by GI losses, renal losses, bleeding, poor oral Na intake, or third spacing of fluids. Volume Depletion and Dehydration
    • Volume resuscitation
    • Discontinue/adjust dose of diuretics.
    • Counsel about hydration and salt intake.
    • Treat underlying cause (e.g., gastroenteritis Gastroenteritis Gastroenteritis is inflammation of the stomach and intestines, commonly caused by infections from bacteria, viruses, or parasites. Transmission may be foodborne, fecal-oral, or through animal contact. Common clinical features include abdominal pain, diarrhea, vomiting, fever, and dehydration. Gastroenteritis, hemorrhage).

Causes of syncope that warrant immediate admission/intervention

Cardiac emergencies:

  • Arrhythmias:
    • Documented, suspected, or induced ventricular tachycardia Ventricular tachycardia Ventricular tachycardia is any heart rhythm faster than 100 beats/min, with 3 or more irregular beats in a row, arising distal to the bundle of His. Ventricular tachycardia is the most common form of wide-complex tachycardia, and it is associated with a high mortality rate. Ventricular Tachycardia:
      • Advanced cardiac life support (ACLS) protocol if indicated
      • Antiarrhythmics
      • Catheter ablation
      • Implantable cardioverter–defibrillator
    • Supraventricular arrhythmias: 
      • ACLS protocol if indicated
      • Antiarrhythmics
      • Catheter ablation
    • Bradyarrhythmias Bradyarrhythmias Bradyarrhythmia is a rhythm in which the heart rate is less than 60/min. Bradyarrhythmia can be physiologic, without symptoms or hemodynamic change. Pathologic bradyarrhythmia results in reduced cardiac output and hemodynamic instability causing syncope, dizziness, or dyspnea. Bradyarrhythmias: permanent pacemakers
  • Ischemic heart disease Ischemic heart disease Coronary heart disease (CHD), or ischemic heart disease, describes a situation in which an inadequate supply of blood to the myocardium exists due to a stenosis of the coronary arteries, typically from atherosclerosis. Coronary Heart Disease (IHD) or acute coronary syndrome (ACS):
    • Activate ACS protocol if indicated.
    • Coronary intervention or cardiac surgery Cardiac surgery Cardiac surgery is the surgical management of cardiac abnormalities and of the great vessels of the thorax. In general terms, surgical intervention of the heart is performed to directly restore adequate pump function, correct inherent structural issues, and reestablish proper blood supply via the coronary circulation. Cardiac Surgery if indicated 
  • Obstruction to left ventricular outflow caused by aortic stenosis Aortic stenosis Aortic stenosis (AS), or the narrowing of the aortic valve aperture, is the most common valvular heart disease. Aortic stenosis gradually progresses to heart failure, producing exertional dyspnea, angina, and/or syncope. A crescendo-decrescendo systolic murmur is audible in the right upper sternal border. Aortic Stenosis
    • Balloon valvuloplasty
    • Aortic valve replacement

Cerebrovascular emergencies:

  • Immediate noncontrast CT of head if cerebrovascular accident (hemorrhagic or ischemic) or intracranial hemorrhage is suspected
  • Appropriate admission/transfer/consultation depending on findings:
    • Neurology
    • Neurosurgery Neurosurgery Neurosurgery is a specialized field focused on the surgical management of pathologies of the brain, spine, spinal cord, and peripheral nerves. General neurosurgery includes cases of trauma and emergencies. There are a number of specialized neurosurgical practices, including oncologic neurosurgery, spinal neurosurgery, and pediatric neurosurgery. Neurosurgery
    • Interventional vascular team:
      • Interventional radiology
      • Interventional vascular surgery Vascular surgery Vascular surgery is the specialized field of medicine that focuses on the surgical management of the pathologies of the peripheral circulation. The main goal of most vascular procedures is to restore circulatory function to the affected vessels by relieving occlusions or by redirecting blood flow (e.g., bypass). Vascular Surgery/neurosurgery
    • Neurologic ICU monitoring

Hemorrhagic emergencies:

  • Hemodynamic stabilization:
    • Volume resuscitation
    • Administration of appropriate blood products
  • Stop/reverse anticoagulation
  • Appropriate surgical consultation if indicated:
    • Gastroenterology
    • Interventional vascular team
    • Obstetrics/gynecology

Differential Diagnosis

  • Seizure: abnormal electrical activity of the neurons in the cerebral cortex Cerebral cortex The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. Cerebral Cortex that can manifest in numerous ways depending on the region of the brain affected. There are numerous etiologies, and investigation of the root cause should be part of the initial evaluation. Diagnosis is made by a clinical evaluation, lab testing, neuroimaging, electroencephalography, and antiseizure drug levels. Treatment is by elimination of the cause, if possible, antiseizure drugs, and surgery when drugs are ineffective. 
  • Traumatic brain injury: physical injury to brain tissue that temporarily or permanently impairs brain function. Traumatic brain injury can be caused by falls, motor vehicle accidents, assaults, and sports activities. Individuals may present with loss of consciousness, confusion, amnesia, seizures, and focal neurologic deficits. Diagnosis is by initial rapid trauma assessment, neurologic examination, and CT scan. Initial treatment is optimizing brain perfusion and supportive care. Severe injuries may require timely surgical intervention.  
  • Intoxication: reversible syndrome associated with substance use, which may cause physical and mental changes (varies depending on the substance that was ingested). Intoxication may lead to accidental death via overdose, and various substances may carry significant complications that increase morbidity and mortality. Management is usually supportive, although some substances have reversible pharmacologic agents. 
  • Conversion disorders: also called functional neurologic symptom disorder. Conversion disorders are psychiatric disorders with prominent motor or sensory impairment that is not compatible with any known neurologic medical condition. The deficits are not consciously produced. Individuals are typically impaired in their social and professional life, but can also be inappropriately unconcerned with their symptoms. Treatment centers around education and psychotherapy Psychotherapy Psychotherapy is interpersonal treatment based on the understanding of psychological principles and mechanisms of mental disease. The treatment approach is often individualized, depending on the psychiatric condition(s) or circumstance. Psychotherapy.

References

  1. McDermott, D. (2020). Approach to the adult patient with syncope in the emergency department. Retrieved September 25, 2021, from https://www.uptodate.com/contents/approach-to-the-adult-patient-with-syncope-in-the-emergency-department
  2. Chen-Scarabelli, C., Scarabelli, T. M. (2004). Neurocardiogenic syncope. BMJ 329:336–341. https://doi.org/10.1136/bmj.329.7461.336
  3. Kharsa A, Wadhwa R. Carotid sinus hypersensitivity. StatPearls. Retrieved September 25, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK559059/
  4. Benditt D. (2021). Syncope in adults: epidemiology, pathogenesis, and etiologies. UpToDate. Retrieved September 1, 2021, from https://www.uptodate.com/contents/syncope-in-adults-epidemiology-pathogenesis-and-etiologies
  5. Benditt D. (2021). Syncope in adults: clinical manifestations and initial diagnostic evaluation. UpToDate. Retrieved September 1, 2021, from https://www.uptodate.com/contents/syncope-in-adults-clinical-manifestations-and-initial-diagnostic-evaluation
  6. Benditt D. (2019). Syncope in adults: management. UpToDate. Retrieved September 2, 2021, from https://www.uptodate.com/contents/syncope-in-adults-management
  7. Thompson A.D., Shea M.J. (2020). Syncope.  MSD Manual Professional Version. Retrieved September 2, 2021, from https://www.msdmanuals.com/professional/cardiovascular-disorders/symptoms-of-cardiovascular-disorders/syncope
  8. Kenaan M., Eagle K. (2018). Syncope. Oxford Medicine Online. Retrieved September 2, 2021, from  https://oxfordmedicine.com/view/10.1093/med/9780190862800.001.0001/med-9780190862800-chapter-6
  9. Morag R. (2017). Syncope. Medscape. Retrieved September 2, 2021, from https://emedicine.medscape.com/article/811669

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