From the Guidelines
Syncope is a temporary loss of consciousness due to insufficient blood flow to the brain, and immediate action should be taken to restore blood flow by lying down flat with legs elevated, and seeking medical attention after the first episode, especially if it occurred without warning, during exercise, or with chest pain, as recommended by the 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope 1.
Causes of Syncope
The causes of syncope can be categorized into several types, including:
- Neurally-mediated (reflex) syncope, such as vasovagal syncope, carotid sinus syncope, and situational syncope
- Orthostatic hypotension, which can be due to volume depletion, autonomic failure, or drug-induced
- Cardiac arrhythmias, such as sinus node dysfunction, atrioventricular conduction system disease, and paroxysmal supraventricular and ventricular tachycardias
- Structural cardiac or cardiopulmonary disease, such as obstructive cardiac valvular disease, acute myocardial infarction, and pulmonary embolus
Diagnosis and Treatment
Diagnosis of syncope involves a thorough history, physical examination, and electrocardiogram (ECG), as well as other tests such as echocardiogram, stress test, and tilt table test, as recommended by the 2017 ACC/AHA/HRS guideline 1. Treatment of syncope depends on the underlying cause, and may include:
- Medications such as midodrine (2.5-10mg three times daily) or fludrocortisone (0.1-0.2mg daily) for orthostatic hypotension
- Beta-blockers such as metoprolol (25-100mg twice daily) for vasovagal syncope
- Pacemaker or implantable cardioverter-defibrillator (ICD) for cardiac arrhythmias
- Addressing underlying conditions such as anemia or dehydration
Prevention
Prevention of syncope episodes involves:
- Staying hydrated
- Avoiding triggers such as prolonged standing
- Gradually changing positions
- Avoiding heavy meals and alcohol
- Getting regular exercise to improve cardiovascular health It is essential to note that the brain can only function for about 8-10 seconds without adequate blood flow, which explains the rapid loss of consciousness when cerebral perfusion drops below critical levels, as stated in the 2017 ACC/AHA/HRS guideline 1.
From the Research
Definition and Classification of Syncope
- Syncope is defined as a brief loss of consciousness due to an abrupt fall in cerebral perfusion 2
- It is characterized by a relatively rapid onset, brief duration with spontaneous and full recovery 3
- The classification of syncope is based on the underlying pathophysiological mechanism causing the event, and includes:
- Cardiac mechanisms
- Orthostatic mechanisms
- Reflex (neurally mediated) mechanisms, which can be further categorized into:
- Vasovagal syncope
- Situational syncope
- Carotid sinus syncope
- Atypical reflex syncope
Causes and Risk Factors of Syncope
- Cardiovascular causes of syncope may be structural (mechanical) or electrical 2
- Orthostatic hypotension is caused by an abnormal drop in systolic blood pressure upon standing, and is defined as a decrease of >20 mmHg in systolic blood pressure or a reflex tachycardia of >20 beats/minute within 3 minutes of standing 2
- The main causes of orthostatic hypotension are autonomic nervous system failure and hypovolaemia 2
- Patients with life-threatening causes of syncope, such as valvular heart disease, cardiomyopathies, and arrhythmias, should be managed urgently and appropriately 4
Diagnosis and Management of Syncope
- A thorough history and physical examination, including orthostatic assessment, are crucial for making the diagnosis of syncope 3, 5
- Short-term risk assessment should be performed to determine the need for admission 3
- In patients with suspected cardiac syncope, monitoring is indicated until a diagnosis is made 3
- In patients with suspected reflex syncope or orthostatic hypotension, outpatient evaluation with tilt-table testing is appropriate 3
- Syncope units have been shown to improve the rate of diagnosis while reducing cost and are highly recommended 3