Syncope is episodic loss of consciousness associated with loss of postural tone. The pathophysiology, involving global hypoperfusion of the brain or brainstem, is distinct from that of seizures. The most common causes of syncope are given in Table 12-9.
Table 12-9.Common Causes of Syncope and Their Prevalence. |Favorite Table|Download (.pdf) Table 12-9. Common Causes of Syncope and Their Prevalence.
| ||Percentage of Patients |
|Neurally mediated causes || |
| Vasovagal ||8-41 |
| Carotid sinus syncope ||0.45 |
|Orthostatic hypotension ||4-10 |
Decreased cardiac output
Obstruction to flow
|Arrhythmias ||4-38 |
|Neurologic and psychiatric diseases ||3-32 |
|Unknown ||13-41 |
et al.. Incidence and prognosis of syncope. N Engl J Med. 2002;347:878–885.
VASOVAGAL SYNCOPE (SIMPLE FAINTS)
Vasovagal syncope occurs in all age groups. Genetic factors may be relevant. Precipitating factors include emotional stimulation, pain, the sight of blood, fatigue, medical instrumentation, blood loss, or prolonged motionless standing. Vagally mediated decreases in arterial blood pressure and heart rate combine to produce CNS hypoperfusion and subsequent syncope. Cerebral ischemia resulting in brief tonic–clonic movements can occur.
Vasovagal episodes generally begin while the patient is in a standing or seated position and only rarely in a horizontal position (eg, with phlebotomy or intrauterine device insertion). A prodrome lasting 30 to 60 seconds usually precedes syncope and can include lassitude, yawning, light-headedness, nausea, pallor, diaphoresis, salivation, blurred vision, and tachycardia.
The patient, who then loses consciousness and falls to the ground, is pale and diaphoretic and has dilated pupils. Breathing continues. The eyes remain open and there is an upward turning of the globes. Bradycardia replaces tachycardia as consciousness is lost. During unconsciousness, abnormal movements may occur, particularly if the patient remains relatively vertical; these are mainly tonic or opisthotonic, but seizurelike tonic–clonic activity is occasionally seen, which can lead to a misdiagnosis of epilepsy. Urinary incontinence may also occur.
The patient recovers consciousness very rapidly (20-30 seconds) after assuming the horizontal position, but residual nervousness, dizziness, headache, nausea, pallor, diaphoresis, and an urge to defecate may be noted. A postictal confusional state with disorientation and agitation either does not occur or is very brief (<30 seconds). Syncope may recur, especially if the patient stands within the next 30 minutes.
Reassurance and a recommendation to avoid precipitating factors are usually the only treatment necessary.
Recurrent vasovagal syncope (also termed neurally mediated or neurocardiogenic syncope) can be diagnosed by inducing syncope during head-up tilt-testing. The bradycardia and hypotension of syncope can be ameliorated by the alpha-agonist midodrine (5 mg three time daily) or with the selective serotonin reuptake inhibitor paroxetine (10-40 mg/d). Tilt-training may have benefit. Artificial pacing is ineffective.
S. Management and therapy of vasovagal syncope: a review. World J Cardiol. 2010;26:308–315.
A cardiovascular cause is suggested when syncope occurs in a recumbent position, during or after physical exertion, or in a patient with known heart disease. Loss of consciousness related to cardiac disease is most often due to an abrupt decrease in cardiac output with resultant cerebral hypoperfusion. Such cardiac dysfunction can result from cardiac arrest, rhythm disturbances (either brady- or tachyarrhythmias), cardiac inflow or outflow obstruction, intracardiac right-to-left shunts, leaking or dissecting aortic aneurysms, or acute pulmonary embolism (Table 12-10). The diagnosis is established by electrophysiologic study and/or long-term event recording. Event monitors triggered by the patient at the onset of symptoms may be helpful and implantable loop recorders, providing continuous EKG recording for up to 3 years, have a high diagnostic yield in unexplained syncope.
Table 12-10.Cardiovascular Causes of Syncope. |Favorite Table|Download (.pdf) Table 12-10. Cardiovascular Causes of Syncope.
|Cardiac arrest |
Paroxysmal atrial tachycardia
Accelerated junctional tachycardia
Postural tachycardia syndrome (POTS)
Torsade de pointes
Mitral valve prolapse (click-murmur syndrome)
Prolonged QT-interval syndromes
Second- or third-degree heart block
Implanted pacemaker failure or malfunction
Sick sinus syndrome (tachycardia-bradycardia syndrome)
Drug toxicity (eg, digitalis, quinidine, procainamide, propranolol, phenothiazines, tricyclic antidepressants, potassium)
Cardiac inflow obstruction
Left atrial myxoma or thrombus
Tight mitral stenosis
Constrictive pericarditis or cardiac tamponade
Cardiac outflow obstruction
|Dissecting aortic aneurysm |
Severe pulmonary vascular disease
Acute pulmonary embolus
V, van Mechelen
R; on behalf of the PICTURE Study Investigators.
et al.. Use of an implantable loop recorder to increase the diagnostic yield in unexplained syncope: results from the PICTURE registry. Europace. 2011;13:262–269.
et al.. Guidelines for the diagnosis and management of syncope (version 2009). Task Force for the Diagnosis and Management of Syncope; European Society of Cardiology (ESC); European Heart Rhythm Association (EHRA); Heart Failure Association (HFA); Heart Rhythm Society (HRS) Eur Heart J. 2009;30:2631–2671.
Cardiac arrest (ventricular fibrillation or asystole) from any cause will result in loss of consciousness in 3 to 5 seconds if the patient is standing or within 15 seconds if the patient is recumbent. Seizurelike activity and urinary and fecal incontinence may be seen as the duration of cerebral hypoperfusion increases.
Supraventricular tachyarrhythmias (atrial or junctional tachycardia, atrial flutter, or atrial fibrillation) may be paroxysmal or chronic. Syncope may be preceded by sudden brief palpitations.
Heart rates faster than 160 to 200/min reduce cardiac output by decreasing the ventricular filling period or inducing myocardial ischemia. Prolonged tachycardia of 180 to 200 beats or more per minute will produce syncope in 50% of normal persons in the upright posture; in patients with underlying heart disease, a heart rate of 135/min may impair cardiac output enough to induce loss of consciousness. Patients with sinus node dysfunction may develop profound bradycardia or even asystole on termination of their tachyarrhythmias. The diagnosis is established when arrhythmias are demonstrated during a symptomatic episode.
In the postural tachycardia syndrome (POTS) that occurs predominantly in young women, an increase in heart rate of 30 or more beats per minute, generally without significant change in blood pressure, occurs on standing from a supine position, and is accompanied by presyncopal and other symptoms.
Ventricular tachyarrhythmias (ventricular tachycardia or multiform, frequent, or paired premature ventricular contractions) are found on prolonged ECG monitoring in some patients with syncope. The syncope associated with ventricular tachycardia is characterized by a very brief prodrome (<5 seconds). The duration of syncope and of the arrhythmia are closely linked. Frequent or repetitive premature ventricular contractions alone do not often coincide with syncopal symptoms but are predictive of sudden death. Elevation of the ST segment in the right precordium of young adults, without structural heart disease (Brugada syndrome), predisposes to ventricular arrhythmias and sudden death. Multiple genes, particularly involving sodium channels, have been implicated.
Mitral valve prolapse (click-murmur syndrome) is a common disorder associated with supraventricular and ventricular arrhythmias and with syncope in a small percentage of patients. Other symptoms include nonexertional chest pain, dyspnea, and fatigue. Serious ventricular arrhythmias and profound bradycardia may occur. The ECG may be normal or show nonspecific ST-T wave changes or frequent premature ventricular contractions. Diagnosis is by echocardiography.
The congenital prolonged QT-interval syndrome consists of paroxysmal ventricular arrhythmias (often torsades de pointes), syncope, and sudden death and is inherited as an autosomal recessive condition associated with deafness or in an autosomal dominant form without deafness. Genes implicated in prolonged QT syndrome include potassium channels (KCNE1, KCNE2, KCNH2, KCNJ2, KCNJ5, KCNQ1), sodium channels (SCN4B, SCN5A), calcium channels (CACNA13), A kinase anchor protein 9 (AKAP9), ankyrin 2 (ANK2), caveolin 3 (CAV3), and α-1 syntrophin (SNTA1). Sporadic cases also occur. Antiarrhymic drugs and electrolyte disorders: (hypomagnesemia, hypocalcemia, hypokalemia) can also produce QT prolongation. Hereditary cases may respond to β-blockers.
Sinoatrial node disease (eg, sick sinus syndrome) may cause syncope with profound sinus bradycardia, prolonged sinus pauses, or sinus arrest with a slow atrial, junctional, or idioventricular escape rhythm. It may be inherited as an autosomal recessive or dominant disorder, caused by mutations in the type V voltage-gated sodium channel alpha subunit (SCN5A) and hyperpolarization-activated cyclic nucleotide-gated potassium channel 4 (HCN4) genes, respectively. Patients should be evaluated promptly by a cardiologist, because a permanent pacemaker is necessary in many cases. In tachycardia-bradycardia syndrome, a form of sick sinus syndrome, both types of arrhythmias occur.
Complete heart block (third-degree atrioventricular block) is a common cause of bradyarrhythmia producing syncope. Permanent atrioventricular conduction abnormalities are easily noted on a routine ECG, but intermittent conduction abnormalities may not be present on a random tracing. A normal PR interval on an ECG obtained after the episode does not exclude the diagnosis of transient complete heart block.
Patients with syncope and documented or suspected complete heart block should be hospitalized promptly. Patients with acute inferior myocardial infarctions are at high risk for atrioventricular block.
CARDIAC INFLOW OBSTRUCTION
Atrial or ventricular myxomas and atrial thrombi usually present with embolic events, but they may also produce a left ventricular inflow or outflow obstruction that results in a sudden decrease in cardiac output, followed by syncope. A history of syncope occurring with change in position is classic but uncommon. Echocardiography can confirm the diagnosis. Surgical removal of the myxoma is indicated.
With constrictive pericarditis or pericardial tamponade, any maneuver or drug that decreases heart rate or venous return can result in suddenly inadequate cardiac output and syncope.
CARDIAC OUTFLOW OBSTRUCTION
Loss of consciousness from congenital or acquired severe aortic stenosis usually occurs after exercise and is often associated with dyspnea, angina, and diaphoresis. The pathophysiology may involve acute left ventricular failure resulting in coronary hypoperfusion and subsequent ventricular fibrillation, or abrupt increases in left ventricular pressure that stimulate baroreceptors, leading to peripheral vasodilation. Echocardiography can help confirm the diagnosis.
Symptomatic aortic stenosis requires valve replacement; without treatment, survival after syncope from aortic stenosis is 18 months to 3 years.
Severe pulmonary stenosis can produce syncope, especially after exertion. A hemodynamic process similar to that occurring in aortic stenosis is responsible.
Hypertrophic cardiomyopathy comprises a group of congenital cardiomyopathies inherited as autosomal dominant disorders of variable severity. Many different genes have been implicated. Symptoms usually begin between the second and fourth decades. Dyspnea is the most common presenting complaint, but syncope occurs in 30% of patients and is the presenting complaint in 10% of patients. Syncope characteristically develops during or after exercise, but orthostatic and posttussive episodes also occur. Syncope may be due to left ventricular outflow obstruction, inflow obstruction, or transient arrhythmias. The diagnosis can be confirmed by echocardiography. Propranolol may control symptoms; an implantable cardioverter defibrillator may terminate potentially fatal ventricular arrhythmias.
DISSECTING AORTIC ANEURYSM
Approximately 5% to 10% of patients with acute aortic dissections present with isolated syncope; other neurologic abnormalities may or may not be present. In 15% of patients, the dissection is painless.
PULMONARY HYPERTENSION & PULMONARY EMBOLUS
Syncope, often exertional, may be the presenting symptom of pulmonary hypertension. A history of exertional dyspnea is usual, and blood gas analysis shows hypoxemia, even at rest. Syncope is the presenting symptom in approximately 20% of patients experiencing massive pulmonary embolism. Upon recovery, such patients often complain of pleuritic chest pain, dyspnea, and apprehension. Hypotension, tachycardia, tachypnea, and arterial hypoxemia frequently accompany these large emboli.
Cerebrovascular disease (Chapter 13, Stroke) is an often suspected but actually uncommon cause of episodic unconsciousness.
BASILAR ARTERY INSUFFICIENCY
Basilar artery transient ischemic attacks usually occur after the sixth decade. The symptom complex of diplopia, vertigo, dysphagia, dysarthria, various sensory or motor symptoms, drop attacks, and occipital headaches suggests diffuse brainstem ischemia. Attacks are typically sudden in onset and brief in duration (seconds to minutes), but when consciousness is lost, recovery is frequently prolonged (30-60 minutes or longer). Isolated unconsciousness without other symptoms of brainstem ischemia is rarely due to basilar artery insufficiency. Two-thirds of patients have recurrent attacks, and strokes eventually occur in approximately one-fifth of all cases. Treatment is discussed in Chapter 13, Stroke.
SUBCLAVIAN STEAL SYNDROME
The subclavian steal syndrome results from subclavian or innominate artery stenosis that causes retrograde blood flow in the vertebral artery, diverting flow from the brainstem and producing hypoperfusion. The degree of subclavian artery stenosis that produces symptoms is variable, but even minor (~40%) stenosis may sometimes do so. A difference between blood pressures measured in the two arms is nearly always found, the average difference being a 45 mm Hg decrease in systolic pressure in the arm supplied by the stenotic vessel. Symptoms of distal limb or vertebrobasilar ischemia may occur. Cerebrovascular risk factors should be modified; stroke is rare. Arteriography and revascularization procedures may be considered.
EY. Unequal blood pressures: a manifestation of subclavian steal. Am J Med. 2011;124:e1–e2.
Syncope occurs in ~10% of patients with migraine during the headache, often on rapid rising to a standing position, suggesting that loss of consciousness is due to orthostatic hypotension; autonomic neuropathy may coexist. Syncopal migraine has both more prolonged unconsciousness and more prolonged recovery than syncope alone. In some patients, basilar migraine produces symptoms similar to those of basilar artery transient ischemic attacks. Antimigraine prophylactic agents (see Chapter 6, Headache & Facial Pain) are often effective in preventing attacks.
et al.. Syncopal migraine. Clin Auton Res. 2012;22:17–23.
Takayasu disease, sometimes referred to as pulseless arteritis, is a panarteritis of the aorta and its major branches that is most common in young Asian women. Symptoms of cerebral hypoperfusion such as impaired vision, confusion, and syncope are often prominent. Generalized symptoms of fever, myalgias, and arthralgias occur. Precipitating factors include exercise, standing, or head movement. Examination reveals decreased or absent brachial pulses with low blood pressures in both arms. The erythrocyte sedimentation rate and C reactive protein may be elevated. Corticosteroid treatment is indicated.
Carotid sinus syncope is uncommon. Men are affected twice as often as women, and most affected individuals are more than 60 years old. Drugs known to predispose to carotid sinus syncope include propranolol, digitalis, and methyldopa. Carotid sinus syncope is diagnosed when carotid sinus massage for 10 seconds results in bradycardia/hypotension (carotid sinus hypersensitivity) and reproduces spontaneous syncope. Carotid sinus hypersensivity without syncope is common in older men. Treatment for symptomatic patients is with pacing.
Carotid sinus syncope may be mistakenly diagnosed when symptoms result from compression of a normal carotid artery contralateral to an occluded internal carotid artery. Carotid sinus massage should not be performed in patients with recent TIA or stroke or with carotid bruit.
C. The natural history of carotid sinus syncope and the effect of cardiac pacing Europace. 2011;13: 462–464.
Orthostatic hypotension occurs more often in men than in women and is most common in the sixth and seventh decades. It may, however, appear even in teenagers. Loss of consciousness usually occurs upon rapidly rising to a standing position, standing motionless for a prolonged period (especially after exercise), or standing after prolonged recumbency (especially in the elderly).
Numerous conditions can produce orthostatic hypotension (Table 12-11), which generally results from either hypovolemia or autonomic dysfunction. The latter may be due to drugs, autonomic neuropathy, or CNS disorders affecting sympathetic pathways in the hypothalamus, brainstem, or spinal cord.
Table 12-11.Causes of Orthostatic Hypotension. |Favorite Table|Download (.pdf) Table 12-11. Causes of Orthostatic Hypotension.
Hypovolemia or hemorrhage
Antidepressants (tricyclics, monoamine oxidase inhibitors)
α and β receptor blockers
Dopaminergic drugs (dopamine agonists, levodopa)
Calcium channel antagonists
Vasodilators (nitroglycerin, sildenafil)
Other neurologic disorders
Idiopathic orthostatic hypotension
Parkinsonism (Parkinson disease, Lewy body dementia, multisystem atrophy)
Posterior fossa tumor
Spinal cord injury with paraplegia
|Cardiac pump failure |
|Prolonged bed rest |
Orthostatic hypotension may also be a feature of neurodegenerative disorders. Idiopathic orthostatic hypotension is associated with isolated degeneration of postganglionic sympathetic neurons. In multisystem atrophy (Shy-Drager syndrome), degeneration of preganglionic sympathetic neurons occurs in combination with parkinsonian, pyramidal, cerebellar, or lower motor neuron signs. These disorders are discussed in Chapter 11, Movement Disorders.
The diagnosis of classic orthostatic hypotension is established by demonstrating a decline in blood pressure of at least 20 mm Hg systolic or 10 mm Hg diastolic within 3 minutes of the patient standing from a lying position. Severe orthostatic intolerance associated with heart rate increases (>120/min) without significant hypotension or syncope is termed postural orthostatic tachycardia syndrome (POTS) and is most common in young women.
A detailed general physical and neurologic examination and laboratory studies (hematocrit, stool occult blood, serum glucose and electrolytes, FTA-ABS, nerve conduction studies) should be directed toward establishing the cause of the disorder.
Any medication (particularly diuretics, venodilators such as nitrates, and vasodilators such as α-agonists) that might be responsible for orthostatic hypotension should be discontinued if possible. The patient should be instructed to stand up gradually, to elevate the head of the bed on blocks, and to use waist-high elasticized support hosiery. Rapid ingestion of 500 mL of water on awakening prior to getting out of bed increases blood pressure for an hour. Other therapy is dictated by the specific cause of hypotension.
The potent mineralocorticoid fludrocortisone has been effective in idiopathic cases and in patients with diabetic neuropathy in doses beginning at 0.1 mg/d orally and increased gradually, as necessary, up to 0.5 mg/d orally. Its mode of action is unclear, but its benefit may relate to increased responsiveness to circulating norepinephrine, as well as an increased plasma volume. Side effects include recumbent hypertension. Alternatively the α-adrenergic receptor agonist midodrine (starting at 2.5 mg two or three times daily) can be used.
S. Medical therapy and physical maneuvers in the treatment of the vasovagal syncope and orthostatic hypotension. Prog Cardiovasc Dis. 2013;55:425–433.
MISCELLANEOUS CAUSES OF SYNCOPE
Cough (tussive) syncope occurs chiefly in middle-aged men with chronic obstructive pulmonary disease but has also been reported in children. Coughing, which need not be prolonged, immediately precedes unconsciousness. Cough syncope may occur while the patient is supine. Prodromal symptoms are absent, and the duration of unconsciousness is brief—often only a few seconds. Full recovery of consciousness occurs promptly. A history of similar episodes is common, and symptoms may be reproduced by having the patient cough on request. The cause may be a decrease in cerebral blood flow from increased intracranial pressure, which results from transmission of cough-induced increased intrathoracic pressure to the intracranial compartment via the spinal fluid or venous connections. Other data support a baroreflex-mediated fall in total peripheral resistance induced by coughing.
The condition is usually benign, and there is no specific treatment except for antitussive drugs such as dextromethorphan.
Micturition syncope is a cerebral hypoperfusion event occurring almost exclusively in men, probably because of the standing position for urination, and is due to peripheral pooling of blood plus vagally induced bradycardia. Episodes can occur immediately before, during, or after micturition. They are more likely to occur at night after the prolonged recumbency of sleep. Urination in a sitting position usually eliminates the symptoms.
Glossopharyngeal neuralgia (see Chapter 6, Headache & Facial Pain) is a rare syndrome characterized by intermittent, agonizing, paroxysmal pain localized to the tonsillar pillar or occasionally to the external auditory meatus. The pain is triggered by contact with or movement of the tonsillar pillars, especially during swallowing or talking. Syncope results from activation of a glossopharyngeal-vagal reflex arc, producing transient bradyarrhythmia leading to cerebral hypoperfusion. Carbamazepine 400 to 1000 mg/d orally will prevent pain and bradycardia in most patients.
Psychogenic syncope is a diagnosis of exclusion and is often made erroneously. Suggestive features are lack of any prodrome, possible secondary gain, bizarre postures and movements, lack of pallor, frequent spells and a prolonged period of apparent unresponsiveness. Eyes are closed during episodes. Psychogenic spells rarely occur when the patient is alone and are rarely associated with incontinence or injury. Most patients are young or have a well-documented history of conversion disorder. Without such a history, diagnosis after the third decade is suspect.
The EEG during psychogenic unconsciousness is normal, without the slowing that typically occurs with cerebral hypoperfusion and follows unconsciousness from a seizure. Caloric testing (see Chapter 3, Coma), which produces nystagmus in conscious patients, and tonic eye deviation in unconscious patients, can distinguish psychogenic unresponsiveness from coma caused by a metabolic or structural lesion.