64 Syncope
Key Points• Syncope is a symptom, not a diagnosis.
• Patients with cardiac syncope have a 6-month mortality rate in excess of 10%.
• If the diagnosis can be made, the disposition will be based on that diagnosis.
• When the patient’s symptoms have resolved and the cause is unclear, risk stratification can help in making decisions on disposition.
• Risk factors in emergency department patients include abnormal electrocardiographic findings, including any rhythm abnormalities detected during monitoring. Other risk factors include a history of cardiac disease (especially congestive heart failure) and absence of a prodrome, which places patients at risk for unfavorable cardiac outcomes. Those with persistently abnormal vital signs, shortness of breath, or a low hematocrit are also at higher risk for other adverse outcomes.
Epidemiology
It is estimated that 1 in 4 people will faint during their lifetime and that 6 in 1000 people per year will suffer from the symptom of syncope. Syncope is responsible for 1% to 2% of all emergency department (ED) visits, and the cost of hospitalization for syncope approaches $2 billion annually.1–4
Pathophysiology
Syncope comes from the Greek word synkoptein, meaning “to cut short.” Hippocrates was the first to use the term and describe the symptom.5 Syncope has many causes, but the pathophysiology of the final pathway is the same: hypoperfusion of the cerebral cortex and reticular activating system, which after 8 to 10 seconds of interrupted perfusion causes loss of consciousness; a shorter period results in lightheadedness or dizziness and is referred to as near syncope.
Classification of Syncope
The American College of Physicians lists four major prognostic categories of syncope: neurally mediated, orthostatic, neurogenic, and cardiac; actually, a fifth category (“syncope of unknown cause”) is recognized because in most cases the cause of the syncope remains unknown even after extensive investigation.6,7
Neurally Mediated Syncope
Neurally mediated syncope is syncope associated with inappropriate vasodilation, bradycardia, or both as a result of inappropriate vagal or sympathetic tone.8 It is a benign type of cardiovascular syncope that is often associated with a sensation of increased warmth and may be accompanied by preceding lightheadedness (prodrome) along with sweating and nausea. A slow, progressive onset suggests the subcategory vasovagal syncope. Sweating and nausea do not occur with orthostatic hypotension, which is another cause of syncope preceded by lightheadedness.5
Orthostatic Syncope
Orthostatic syncope occurs in individuals with documented postural hypotension associated with syncope or symptoms of presyncope.4 In cases of orthostatic syncope, measurement of blood pressure is recommended, first after the patient is supine for 5 minutes and then after the patient is able to stand for 1 to 3 minutes. A decrease of more than 20 mm Hg in systolic pressure is considered abnormal, as is a drop in pressure below 90 mm Hg independent of the development of symptoms.9
Because orthostatic hypotension occurs in asymptomatic individuals, vital signs are neither particularly sensitive nor specific. In fact, positive orthostatic changes have been documented in up to 40% of asymptomatic patients older than 70 years and in 25% of those younger than 60 years. Similarly, a notable number of children who are asymptomatic have been documented to have orthostatic hypotension.5,10
The most common cause of orthostatic syncope is intravascular volume loss, which may be due to dehydration or bleeding. Orthostatic syncope is not always benign because many patients with serious causes can have this symptom.11
Neurologic Syncope
Most cases involving neurologic causes of syncope are easily predicted. In general, when these patients have symptoms suggesting a specific disease process, the need for intervention based on neurologic symptoms is usually obvious. It is not recommended that a routine neurologic work-up be performed in all patients with syncope unless related neurologic symptoms are present. It has been determined that routine neurologic testing and investigation, such as computed tomography (CT), is not cost-effective in patients without neurologic symptoms.12
Cardiac-Related Syncope
Cardiac-related syncope is clearly the most dangerous class of syncope, and it can be a harbinger of sudden death. Because patients with documented cardiac syncope have a 6-month mortality rate of greater than 10%, timely and thorough evaluation is warranted.13
Syncope of Unknown Cause
Syncope of unknown cause is the largest category of syncope, with estimates as high as 40%, even with extensive work-up.1 Some studies have found that after evaluation in the ED, physicians are uncertain of the cause of the syncope more than 50% of the time.14
