Flashcards in Chapter 27 - Syncope Deck (57)
How does one define syncope?
"Syncope is a transient, self-limited loss of consciousness due to acute global impairment of cerebral blood flow. The onset is rapid, duration brief, and recovery spontaneous and complete."
Vertebrobasilar ischemia might be considered a cause of syncope.
True or False?
Vertebrobasilar ischemia will lead to hypoperfusion of the posterior cerebral cortex, cerebellum and medulla. Since syncope is considered a transient global ischemia, localized hypoperfusion due to involvement of selected brain vessels with loss of counsciounsness, while sharing some similarities to syncope, is not seen as a cause of one.
Name the differential diagnosis for syncope.
Seizures, vertebrobasilar ischemia, hypoxemia, and hypoglycemia.
A syncopal prodrome (presyncope) is common, although loss of consciousness may ocur without any warning symptoms. Which symptoms should one expect in presyncope?
"Typical presyncopal symptoms include dizziness, lightheadedness or faintness, weakness, fatigue, and visual and auditory disturbances."
Categorize the causes of syncope.
(1) neurally mediated syncope (also called reflex or vasovagal syncope);
(2) orthostatic hypotension;
(3) cardiac syncope.
Summarize the different pathophysiology of the three categories of syncope.
"Neurally mediated syncope comprises a heterogeneous group of functional disorders that are characterized by a transiet change in the reflexes responsible for maintaining cardiovascular homeostasis. Episodic vasodilation (or loss of vasoconstrictor tone) and bradycardia occur in varying combinations, resulting in temporary failure of blood pressure control. In contrast, in patients with orthostatic hypotension due to autonomic failure, these cardiovascular homeostatic reflexes are chronically impaired. Cardiac syncope may be due to arrhythmias or structural cardiac diseases that cause a decrease in cardiac output. The clinical features, underlying pathophysiologic mechanisms, therapeutic interventions, and prognoses differ markedly among these three causes."
Summarize the Epidemiology regarding syncope as a cause of emergency room visits, annual cost due to hospitalization, cumulative incidence during lifetime, and differences in its features related to the patient's age and sex.
"Syncope is a common presenting problem, accounting for approximately 3% of all emergency room visits and 1% of all hospital admissions. The annual cost for syncope-related hospitalization in the United States is ~$2,4 billion. Syncope has a lifetime cumulative incidence of up to 35% in the general population. The peak incidence occurs between ages 10 and 30 years, with a median peak around 15 years. Neurally mediated syncope is the etiology in the vast majority of these cases. In elderly adults, there is a sharp rise in the incidence of syncope after 70 years."
What is the most common cause of syncope?
The elderly are at increased risk for syncope. How can one explain this finding?
"Orthostatic hypotension also increases in prevalence with age because of the baroreflex responsiveness, decreased cardiac compliance, and attenuation of the vestibulosympathetic reflex associated with aging. In the elderly, orthostatic hgypotension is substantially more common in institutionalized (54-68%) than community-dwelling (6%) individuals, an observation most likely explainted by the greater prevalence of predisposing neurologic disorders, physiologic impairment, and vasoactive medication use among institutionalized patients."
After a syncopal episode, the prognosis includes an increased mortality rate compared to the general population.
True or False?
False: "The prognosis after a single syncopal event for all age groups is generally benign. In particular, syncope of noncardiac and unexplained origin in younger individuals has an excellent prognosis; life expectancy is unaffected.
True: "By contrast, syncope due to a cardiac cause, either structural heart disease or primary arrhythmic disease, is associated with an increased risk of sudden cardiac death and mortality from other causes. Similarly, mortality rate is increased in individuals with syncope due to orthostatic hypotension related to age and the associated comorbid conditions."
Summarize the pathophysiology of syncope. Make a correlation between the pooling of blood and the reduced cerebral blood flow.
"The upright posture imposes a unique physiologic stress upon humans; most, although not all, syncopal episodes occur from a standing position. Standing results in pooling of 500-1000mL of blood in the lower extremities and splanchnic circulation. There is a decrease in venous return to the heart and reduced ventricular filling that result in diminished cardiac output and blood pressure. These hemodynamic changes provoke a compensatory reflex response, initiated by the baroreceptors in the carotid sinus and aortic arch, resulting in increased sympathetic outflow and decreased vagal nerve activity. The reflex increases peripheral resistance, venous return to the heart, and cardiac output and thus limits the fall in blood pressure. If this response falls, as is the case chronically in orthostatic hypotension and transiently in neurally mediated syncope, cerebral hypoperfusion occurs."
"Syncope is a consequence of global cerebral hyopperfusion and thus represents a failure of cerebral blood flow autoregulatory mechanisms. Myogenic factors, local metabolites, and to a lesser extent autonomic neurovascular control are responsible for the autoregulation of cerebral blood flow. The latency of the autoregulatory response is 5-10 s. Typically cerebral blood flow ranges from 50 to 60 mL/min per 100 g brain tissue and remains relatively constant over perfusion pressures ranging from 50 to 150 mmHg. Cessation of blood flow for 6-8 s will result in loss of consciousness, while impairment of consciousness ensues when blood flow decreases to 25mL/min per 100 g brain tissue."
Name the causes of reduced cardiac output related to syncope.
Decreased effective circulating blood volume; increased thoracic pressure; massive pulmonary embolus; cardiac brady- and tachyarrhythmias; valvular heart disease; and myocardial dysfunction."
Name the causes of reduced systemic vascular resistance.
Central and peripheral autonomic nervous system diseases, sympatholytic medications, and transiently during neurally mediated syncope.
Name the causes of increased cerebral vascular resistance.
"Increased cerebral vascular resistance, most frequently due to hypocarbia induced by hyperventilation, may also contribute to the pathophysiology of syncope."
Which patterns of electroencephalographic (EEG) might one observe during a syncopal event?
"Two patterns of electroencephalographic (EEG) changes occur in syncopal subjects. The first is a "slow-flat-slow" pattern in which normal backgroud activity is replaced with high-amplitude slow delta waves. This is followed by sudden flattening of the EEG - a cessation or attenuation of cortical activity - followed by the return of slow waves, and then normal activity. A second pattern, the "slow pattern", is characterized by increasing and decrasing slow wave activity only. The EEG flattening that occurs in the slow-flat-slow pattern is a marker of more severe cerebral hypoperfusion. Despite the presence of myoclonic movements and other motor activity during some syncopal events, EEG sizure discharges are not detected."
In order to elitic neurally mediated syncope, a functioning autonomic nervous system is necessary, in contrast to syncope resulting from autonomic failure.
True or False?
Neurally mediated syncope might be subdivided. Explan this subclassification and its pathophysiological mechanisms.
"Neurally mediated syncope may be subdivided based on the afferent pathway and provocative trigger. Vasovagal syncope (the common faint) is provoked by intense emotin, pain, and/or orthostatic stress, whereas the situational reflex syncopes have specificed localized stimuli that provoke the reflex vasodilation and bradycardia that leads to syncope. The underlying mechanisms have been identified and pathophysiology delineated for most of these situational reflex syncopes. The afferent trigger may originate in the pulmonary system, gastrointestinal system, urogenital system, heart, and carotid artery. Hyperventilation leading to hypocarbia and cerebral vasoconstriction, and raised intrathoracic pressure that impairs venous return to the heart, play a central role in many of the situation reflex syncopes. The afferent pathways of the reflex arc differs among these disorders, but the efferent response via the vagus and sympathetic pathways is similar."
Summarize the features of neurally mediated syncope, as well as the differences between a syncopal episode and seizure.
"In addition to symptoms of orthostatic intolerance such as dizziness, lightheadedness, and fatigue, premonitory features of autonomic activation may be present in patients with neurally mediated syncope. These include diaphoresis, pallor, palpitations, nausea, hyperventilation, and yawning. During the syncopal event, proximal and distal myoclonus (typically arrhythmic and multifocal) may occur, raising the possibility of epilepsy. The eys typically remain open and usually deviate upward. Pupils are usually dilated. Roving eye movements may occur. Grunting, moaning, snorting, and stertorous breathing may bepresent. Urinary incontinence may occur. Fecal incontinence is very rare. Postictal confusion is also rare, although visual and auditory hallucinations and near death and out-of-body experiences are sometimes reported."
Give examples of known predisposing factors and provocative stimuli for neurally mediated syncope.
Motioless upright posture, warm ambient temperature, intravascular volume depletion, alcohol ingestion, hypoxemia, anemia, pain, the sight of blood, venipuncture, and intense emotion.
Are there any maneuvers that avoid or delay syncope? Is there any available evidence for these?
Yes. "Isometric counterpressure maneuvers of the limbs (leg crossing or handgrip and arm tensing) may raise blood pressure by increasing central blood volume and cardiac output by increasing central blood volume and cardiac output. By maintaining pressure in the autoregulatory zone, these maneuvers avoid or delay the onset of syncope. Randomized controlled trials support this intervention."
Which pharmacotherapies might be used in neurally mediated syncope? Is there any avaible evidence for their use?
"Fludrocortisone, vasoconstricting agents, and beta-adrenoreceptor antagonists are widely used by experts to treat refractory patients, although there is no consistent evidence from randomized controlled trials for any pharmacotherapy to treat neurally mediated syncope."
Are there any patients with neurally mediated syncope who might benefit from pacemaker implantation?
"Because vasodilation is the dominant pathophysiologic syncopal mechanism in most patients, use of a cardiac pacemaker is rarely beneficial. Possible exceptions are older patients (>40 years) in whom syncope is associated with asystole or severe bradycardia and patients with prominent cardioinhibition due to carotid sinus syndrome. In these patients, dual-chamber pacing may be helpful."
How does one define orthostatic hypotension? Compare it to the definition of pulsus paradoxus.
"Orthostatic hypotension, defined as a reduction in systolic blood pressure of at least 20 mmHg or diastolic blood pressure of at least 10 mmHg within 3 min of standing or head-up tilt on a tilt table, is a manifestation of sympathetic vasoconstrictor (autonomic) failure."
Pulsus paradoxus is a decrease in at least 10 mmHg of systolic blood pressure during inspiration.
Make a comparison between "delayed" and "initial orthostatic hypotension.
"A variant of orthostaic hypotension is "delayed" orthostatic hypotension, which occurs beyond 3 min of standing; this may reflect a mild or early form of sympathetic adrenergic dysfunction. In some cases, orthostatic hypotension occurs within 15 s of standing (so-called "initial" orthostatic hypotension), a finding that may reflect a transiet mismatch between cardiac output and peripheral vascular resistance and does not represent autonomic failure."
Summarize the findings in orthostatic hypotension.
"Characteristic symptoms of orthostatic hypotension include ligheadedness, dizziness, and presyncope (near-faintness) ocurring in response to sudden postural change. However, symptoms may be absent or nonspecific, such as generalized weakness, fatigue, cognitive slowing, leg buckling, or headache. Visual blurring may occur, likely due to retinal or occipital lobe ischemia. Neck pain, typically in the suboccipital, posterior cervical, and shoulder region (the "coat-hanger headache"), most likely due to neck muscle ischemia, may be the only symptom. Patients may report orthostatic dyspnea (thought to reflect ventilation-perfusion mismatch due to inadequate perfusion of ventilated lung apices) or angina (attributed to impiared myocardial perfusion even with normal coronary arteries). Symptoms may be exacerbated by exertion, prolonged standing, increased ambient temperature, or meals. Syncope is usually preceded by warning symptoms, but may occur suddenly, suggesting the possibility of a seizure or cardiac cause."
How does one define supine hypertension? How frequent is it? Is there any correlation to orthostatic hypotension and its treatment?
"Supine hypertesion is common in patients with orthostaic hypotension due to autonomic failure, affecting over 50% of patients in some series. Orthostatic hypotension may present after initiation of therapy for hypertension, and supine hypertension may follow treatment of orthostatic hypotension. However, in other cases, the associtation of the two conditions is unrelated to therapy; it may in part be explained by baroreflex dysfunction in the presence of residual sympathetic outflow, particularly in patients with central autonomic degenration."
Besides orthostatic hypotension and supine hypertension, which organs might be affected by autonomic dysfunction?
"Autonomic dysfunction of other organ systems (including bladder, bowels, sexual organs, and sudomotor system) of varying severity frequently accompanies orthostatic hypotension in these disorders."
Name the central causes for orthostatic hypotension and their main feature.
"The primary autonomic degenerative disorders are multiple system atrophy (the Shy-Drager syndrome), Parkinson's disease, dementia with Lewy bodies, and pure autonomic failure. These are often grouped together as "synucleinopathies" due to the presence of alpha-synuclein, a small protein that precipitates predominantly in the cytoplasm of neurons in the Lewy body disorders (Parkinson's disease, dementia with Lewy bodies, and pure autonomic failure) and in the glia in multiple system atrophy."
Name the peripheral causes for orthostatic hypotension.
"Peripheral autonomic dysfunction may also accompany small-fiber peripheral neuropathies such as those seen diabetes, amyloid, immune-mediated neuropathies, hereditary sensory and autonomic neuropathies (HSAN; particularly HSAN type III, familial dysautonomia), and inflammatory neuropathies. Less frequently, orthostatic hypotension is associated with the peripheral neuropathies that accompany vitamin B12 deficiency, neurotoxic exposure, HIV and other infections, and porphyria."
What is the correlation between syncope and food?
"Patients with autonomic failure and the elderly are susceptible to falls in the blood pressure associated with meals. The magnitude of the blood pressure fall is exacerbated by large meals, meals high in carbohydrate, and alcohol intake. The mechanism of postprandial syncope is not fully elucidated."
Name the causes of iatrogenic orthostatic hypotension.
"Orthostatic hypotension is often iatrogenic. Drugs from several clases may lower peripheral resistance (e.g., alpha-adrenoreceptor antagonists used to treat hypertension and prostatic hypertrophy; antihypertensive agents of several classes; nitrates and other vasodilators; tricyclic agents and phenothiazines). Iatrogenic volume depletion due to diuresis and volume depletion due to medical causes (hemorrhage, vomiting, diarrhea, or decreased fluid intake) may also result in decreased effective circulatory volume, orthostatic hypotension, and syncope."
Summarize the nonpharmacological and pharmacological therapies for orthostatic hypotension.
"The first step is to remove reversible causes - usually vasoactive medications. Next, nonpharmacologic interventions should be introduced. These interventions include patient education regarding staged moves from supine to upright; warnings about the hypotensive effects of large meals; intructions about the isometric counterpressure maneuvers that increase intravascular pressure; and raising the head of the bed to recude supine hypertension. Intravascular volume should be expanded by increasing dietary fluid and salt. If these nonpharmacologic measures fail, pharmacologic intervention with fludrocortisone acetate and vasocontricting agents such as midodrine, L-dihydroxyphenylserine, and pseudoephedrine should be introduced. Some patients with intractable symptoms require additional therapy with supplementary agents that include pyridostigmine, yohimbine, desmopressin acetate (DDAVP), and erythropoietin."
Name the bradyarrhythmias that migh be associated with syncope as well as its designation.
"Bradyarrhythmias that cause syncope include those due to severe sinus node dysfunction (e.g., sinus arrest or sinoatrial block) and atrioventricular (AV) block (e.g., Mobitz type II, highgrade, and complete AV block). The bradyarrhythmias due to sinus node dyusfunction are often associated with an atrial tachyarrhythmia, a disorder known as the tachycardia-bradycardia syndrome. A prolonged pause following the termination of a tachycardic episode is a frequent cause of syncope in patients with the tachycardia-bradycardia syndrome. Medications of several classes may also cause bradyarrhythmias of sufficient severity to cause syncope. Syncope due to bradycardia or asystole is referred to as Stokes-Adams attack."
Explain the pathophysiology of syncope due to ventricular tachyarrhythmia.
"The likelihood of syncope with ventricylar tachycardia is in part dependent on the ventricular rate; rates below 200 beats/min are less likely to cause synope. The compromised hemodynamic function during ventricular tachycardia is caused by ineffective ventricular contraction, reduced diastolic filling due to abbreviated filling periods, loss of AV synchrony, and concurrent myocardial ischemia."
Name the hereditary ventricular tachyarrhythmias that might be associated with syncope.
Long QT syndrome, Brugada syndrome, and cathecolaminergic polymorphic ventricular tachycardia.
Summarize the features of long QT syndrome as well as the mutations most associated with this syndrome.
"The long QT syndrome is a genetically heterogeneous disorder associated with prolonged cardiac repolarization and a predisposition to ventricular arrhythmias. Syncope and sudden death in patients with long QT syndrome result from a unique polymorphic ventricular tachycardia called torsades des pointes that degenerates into ventricular fibrillation. The long QT syndrome has been linked to genes encoding K+ channel alpha-subunits, K+ channel beta-subunits, voltage-gated Na+ channel, and a scaffolding protein, ankyrin B (ANK2)."
Summarize the features of Brugada syndrome.
"Brugada syndrome is characterized by idiopathic ventricular fibrillation in association with right ventricular electrocardiogram (ECG) abnormalities without structural heart disease. This disorder is also genetically heterogeneous, although it is most frequently linked to mutation in the Na+ channel alpha-subunit, SNC5A."
Summarize the features of catecholaminergic polymorphic ventricular tachycardia.
"Catecholaminergic polymorphic tachycardia is an inherited, genetically heterogeneous disorder associated with exercise- or stress-induced ventricular arrhythmias, syncope, or sudden death."
Acquired long QT interval is most commonly due to drugs, and might lead to sudden death due to ventricular tachyarrhythmias.
True or False?
Heart structural disease syncope is mostly due to dimished cardiac output. Is there any other mechanisms that might explain the correlation between heart structural disease and syncope?
"Structural heart disease (e.g., valvular disease, myocardial ischemia, hypertrophic and other cardiomyopathies, cardiac masses such as atrial myxoma, and pericardial effusions) may lead to syncope by compromising cardiac output. Structural disease may also contribute to other pathophysiologic mechanisms of syncope. For example, cardiac structural disease may predispose to arrhythmogenesis; aggressive treatment of cardiac failure with diuretics and/or vasodilators may lead to orthostatic hypotension; and inappropriate reflex vasodilation may occur with strctural disorders such as aortic stenosis and hypertrophic cardiomyopathy, possible provoked by increased ventricular contractility."
How does one differentiate abnormal movements during a syncopal event from that of a seizure?
"Whereas tonic-clonic movements are the hallmark of a generalized seizure, myoclonic and other movements also may occur in up to 90% of syncopal episodes. Myoclonic jerks associated with syncope may be multifocal or generalized. They are typically arrhythmic and of short duration (less than 30 s). Mild flexor and extensor posturing also may occur. Partial or partial-complex seizures with secondary generalization are usually preceded by an aura, commonly an unpleasant smell; fear; anxiety; abdominal discomfort; or other visceral sensations."
Describe autonomic epilepsy as well as its differential diagnosis.
"Autonomic seizures have cardiovascular, gastrointestinal, pulmonary, urogenital, pupillary, and cutaneous manifestatios that are similar to the premonitory features of syncope. Furthermore, the cardiovascular manifestations of autonomic epilepsy include clinically significant tachycardias and bradycardias that may be of sufficient magnitude to cause loss of consciousness. The presence of accompanying non-autonomic auras may help differentiate these episodes from syncope."
Muscle aches may occur after both syncope and seizures, although they tend to last longer and be more severe following a seizure.
True or False?
How does one distinguish a loss of consciousness due to hypoglicemia versus syncope?
"Hypoglicemia may cause transiet loss of consciousness typically in individuals with type 1 or type 2 diabetes treated with insulin. The clinical features associated with impending or actual hypoglycemia include tremor, palpitations, anxiety, diaphoresis, hunger and paresthesias. These symptoms are due to autonomic activation to counter the falling blood glucose. Hunger, in particular, is not a typicaly premonitory feature of syncope. Hypoglycemia also impairs neuronal function, leading to fatigue, weakness, diziness, and cognitive and behavioral symptoms. Diagnostic difficulties may occur in individuals in strict glycemic control; repeated hypoglycemia impairs the counterregulatory response and leads to a loss of characteristic warning symptoms that are the hallmark of hypoglycemia."
How do you define cataplexy? How frequently does it occur in narcolepsy?
"Patients with cataplexy experience an abrupt partial or complete loss of muscuar tonse triggered by strong emotions, typically anger or laughter. Unlike syncope, consciousness is maintained throughout the attacks, which typically last between 30 s and 2 min. There are no premonitory symptoms. Cataplexy occurs in 60-75% of patients with narcolepsy."
Name the gait disorders that might lead to falls and might have to be considered in the differential diagnosis of syncope.
"The clinical interview and interrogation of eyewitnesses usually allow differentiation of syncope from falls due to vestibular dysfunction, cerebellar disease, extrapyramidal system dysfunction, and other gait disorders. If the fall is accompanied by head trauma, a postconcussive syndrome, amnesia for the precipitating events, and/or the presence of loss of consciousness may contribute to diagnostic difficulty."
Name the psychiatric disorders that should be considered in the differential diagnosis of syncope.
Generalized anxiety, panic disorders, major depression, and somatization disorder.
After a thorough clinical history, physical examination and ECG, how many patients will have a diagnosis elucidating the etiology of syncope?
Give examples of autonomic testing of the sympathetic nervous system and their usefulness.
"Autonomic testing is helpful to uncover objective evidence of autonomic failure and also to demonstrate a predisposition to neurally mediated syncope. Autonomic testing includes assessments of parasympathetic autonomic nervous system function (e.g., heart rate variability to deep respiration and a Valsalva maneurver), sympathetic cholinergic function (e.g., thermorregulatory sweat response and quantitative sudomotor axon reflex test), and sympathetic adrenergic function (e.g., blood pressure response to a Valsalva maneuver and a tilt-table test with beat-to-beat blood pressure measurement)."
Why should one test the autonomic function with a tilt-table test?
"The hemodynamic abnormalities demonstrated on tilt-table test may be useful in distinguishing orthostatic hypotension due to autonomic failure from hypontesive bradycardic response of neurally mediated syncope. Similarly, the tilt-table test may help identifiy patients with syncope due to immediate or delayed orthostatic hypotension."
When should one carry a carotid sinus massage testing? Is there any risk for this test? And if so, which patients have a higher risk?
"Carotid sinus massage should be considered in patients with symptoms suggestive of carotid sinus syncope and in patients over age 50 years with recurrent syncope of unknown. This test should only be carried out under continuous ECG and blood pressure monitoring and should be avoided in patients with carotid bruits, plaques, or stenosis."
Name the indications for hospital monitoring due to syncope.
"Patients should be monitored in hospital if the likelihood of a life.threatening arrhythmia is high, e.g., patients with severe structural or coronary artery disease, nonsutained ventricular tachycardia, trifascicular heart block, prolonged QT interval, Brugada syndrome ECG pattern, or family history of sudden cardiac death."
When should one consider Holter or loop recorder outpatient monitoring?
"Holter monitoring is recommended for patients who experience frequent syncopal episodes (one or more per week), whereas loop recorders, which continually record and erase cardiac rhythm, are indicated for patients with suspected arrhythmias with low risk of sudden cardiac death. Loop recorders may be external (recommended for evaluation of episodes that occur at a frequency of greater than one per month) or implantable (if syncope occurs less frequently)."
Which conditions associated with syncope might be diagnosed with echocardiography? Is there any other utility regarding this test?
"Echocardiographic diagnoses that may be responsible for syncope include aortic stenosis, hypertrophic cardiomyopathy, cardiac tumors, aortic dissection, and pericardial tamponade. Echocardiography also has a role in risk stratification based on the left ventricular ejection fraction."
When should one investigate syncope with treadmill exercise testing?
"Treadmill testing may help identify exercise-induced arrhythmias (e.g., tachycardia-related AV block) and exercise-induced exaggerated vasodilation."
Electrophysiologic studies are very sensible and specific and thus often used to investigate syncope.
True or False?