In this post, I link to and excerpt from StatPearls‘ [Link is to Table Of Contents] Syncope, Shamai A. Grossman; Madhu Badireddy. Last Update: June 21, 2022.
All that follows is from the above resource.
Introduction
Syncope is caused by decreased cerebral blood flow leading to transient loss of consciousness and postural tone, associated with spontaneous recovery. Symptoms like dizziness, lightheadedness, diaphoresis, nausea, and visual disturbances may precede it or occur suddenly with none of the above symptoms. Syncope is a symptom described as fainting, blacking out, falling out, or “having a spell,” and represents 1 to 3.5% of all emergency department visits and 6% of all hospital admissions in the United States. This large number of emergency department visits and admissions reflect the varied etiologies of syncope from benign to life-threatening and the high degree of diagnostic uncertainty associated with this symptom.
Etiology
Syncope is a symptom of an underlying disease process rather than a disease itself. Although syncope mimics a death-like experience eliciting extreme consternation among both patients and their families, most syncopal events have a benign cause. Benign causes of syncope reflect vasovagal (also known as neurocardiogenic), volume depletion, or medication-related etiologies. More ominous causes are related to dysrhythmia and valvular abnormalities such as ventricular tachycardia, atrioventricular (AV) block, or critical aortic stenosis. A history of left ventricular dysfunction (with concomitant degeneration of the conduction system leading toward a propensity for dysrhythmias) has been found to be the most ominous predictor of an adverse etiology of a syncopal event.
Causes of Syncope
1. Cardiovascular disorders
2. Cerebrovascular causes (vertebrobasilar insufficiency)
3. Disorders of blood flow and vascular tone
4. Others that mimic syncope
Vasovagal Syncope (Neurocardiogenic syncope, Common faint)
This accounts for almost 50% of all cases of syncope. When faced with certain situations like prolonged standing, crowded places, hot environment, severe pain, extreme fatigue and stress leads to vasodilatation (sympathetic withdrawal) and bradycardia (parasympathetic activity). This condition is also called common faint as it is the common cause of syncope and can occur even in normal people. Syncope events are preceded by prodromal symptoms like blurred vision, diaphoresis, nausea, dizziness, weakness, and then leads to bradycardia, decreased blood pressure, and then lose consciousness. Patients appear pale to the onlookers. Patients normally regain consciousness in few minutes and may experience generalized weakness. They do not lose sphincter control, rarely have any tonic-clonic activity or confusion after regaining consciousness as in patients with seizures.
Epidemiology
Syncope accounts for around 1 to 3.5% of visits to emergency department visits in the US. Syncope is more common in older patients due to multiple comorbidities and multiple medications. Cardiac etiology is more common in older patients and noncardiac etiology (vasovagal) common in young adults. There is no significant difference in incidence between men and women.
Pathophysiology
The brain needs a constant supply of glucose (through adequate cerebral blood flow) to function and any interruption to this even for few seconds can lead to loss of consciousness or syncope. Cerebral blood flow is maintained by a complex mechanism involving cardiac output, systemic vascular resistance, mean arterial pressure, and intravascular volume. Any defect in one or more of these systems leads to decreased cerebral blood flow. Approximately three-fourths of blood is in the venous bed and any interference in venous return can lead to decreased cardiac output.
Any episode lasting more than a few minutes is not syncope and is more likely to be related to a seizure or other acute neurologic process. Seizures are the most common disease misdiagnosed as syncope. When symptoms overlap too closely, the only way to differentiate seizure from syncope may be with an EEG.
Terms near syncope or presyncope are confusing in that they may convey a different meaning to different practitioners. However, when a practitioner defines near syncope as “a feeling that you were going to pass out but did not” then, near syncope and syncope are both thought to be related to cerebral hypoperfusion, and therefore, any disease process which decreases blood flow can cause syncope and near syncope.
History and Physical
The position of the patient at the time of the event is important. Syncope in a standing position can suggest vasovagal and in a supine position can be due to neurocardiac causes.
The physical examination in syncope should center around vital sign abnormalities as these can often suggest underlying disease processes such as orthostatic hypotension or cardiovascular compromise.
Detailed cardiovascular and neurologic examinations should be included looking for signs of vascular disease, congestive heart failure, or an acute cerebrovascular event masquerading as syncope.
Evaluation
Testing rarely leads to a diagnosis as the most common cause is vasovagal and benign
In patients presenting to the Emergency department, routine blood work to include hemoglobin, electrolytes, and glucose is indicated. At the minimum ECG is needed in all patients presenting with syncope.
If cardiovascular etiology suspected, further workup includes cardiac enzymes, continuous cardiac monitoring, and echocardiogram. Holter monitor recommended for outpatients suspected of conduction abnormalities.
If cerebrovascular etiology suspected, further workup includes CT head, carotid Doppler ultrasound, MRI brain, and MRA.
Electroencephalography (EEG) indicated if seizures suspected.
A tilt table test is indicated in:
The ECG is the most useful diagnostic study, yielding an etiology of syncope in approximately 5% of patients, while routine blood work leads to a diagnosis in only about 2% of cases. Despite widespread and often indiscriminate testing, approximately 45% of patients will leave the emergency department without a diagnosis following their syncopal event. Recent data suggests that a focused management plan may help diagnose an etiology of the syncopal event and reduce the number of patients discharged without a diagnosis. For example, echocardiography before discharge may be useful in uncovering valvular disease in a patient presenting with a murmur and syncope. Similarly, overnight telemetry or discharge with an event monitor may help expose a dysrhythmia in a patient with evidence of conduction disease on their presenting ECG.[1][2]
Pearls and Other Issues
Vasovagal syncope is the most common type of syncope.
Mostly benign but can be life-threatening in patients with underlying cardiac arrhythmia.
ECG is the most useful test in syncope, but its diagnostic yield is only 5%, leaving careful history and physical examination as the most valuable tools in evaluating a syncopal event.
Following a syncopal event, patients should be instructed not to drive or operate heavy machinery at least until the completion of their workup or follow up with their primary care provider.
Mental illness and substance abuse should be considered in syncope patients where the etiology of syncope remains unclear. [5]
Enhancing Healthcare Team Outcomes
Most of the patients with emergency room visits for syncope do not have a diagnosis at discharge. Even hospitalized patients leave the hospital with unclear etiology for their syncope. The majority of times the cause is benign but patients need close outpatient follow-up to make sure there is a cause identified and does not recur. This needs close follow-up with a primary care physician and cardiology.
