From the Guidelines
Syncope is primarily caused by cerebral hypoperfusion, which can be due to various factors including vasovagal syncope, cardiac issues, orthostatic hypotension, and neurological conditions, as stated in 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 broadly categorized into:
- Cardiac (cardiovascular) syncope, which is caused by bradycardia, tachycardia, or hypotension due to low cardiac index, blood flow obstruction, vasodilatation, or acute vascular dissection 1
- Noncardiac syncope, which includes reflex syncope, orthostatic hypotension, volume depletion, dehydration, and blood loss 1
- Reflex (neurally mediated) syncope, which is caused by a reflex that leads to vasodilation, bradycardia, or both 1
- Vasovagal syncope (VVS), which is the most common form of reflex syncope, mediated by the vasovagal reflex and often triggered by emotional stress, pain, or prolonged standing 1
Diagnostic Approach
The diagnostic approach to syncope involves a thorough history, physical examination, and ECG, as recommended by the 2021 ACR Appropriateness Criteria for syncope 1.
- A detailed history and physical examination can help identify the underlying cause of syncope and guide further testing
- An ECG is recommended for all patients to detect arrhythmias or abnormality indicative of higher risk for arrhythmia
- Additional laboratory, physiologic, and image-based testing should be limited to select patients based on clinical assessment
Management
The management of syncope involves:
- Initial management with placement in a supine position with legs elevated to restore blood flow to the brain
- Preventive measures for recurrent vasovagal syncope, such as increasing salt and fluid intake, avoiding triggers, and using compression stockings
- Medications like fludrocortisone or midodrine may be prescribed to maintain blood pressure in some cases
- Beta-blockers might be used for cardiac-related syncope It is essential to determine the underlying cause of syncope, as cardiac syncope can indicate serious heart conditions requiring specific treatment, as highlighted in the 2006 AHA/ACCF scientific statement on the evaluation of syncope 1.
From the Research
Causes of Syncope
The causes of syncope can be classified into several categories, including:
- Cardiac causes: These may be structural (mechanical) or electrical, and can include arrhythmias, which are the most common cardiac causes of syncope 2.
- Reflex (neurally mediated) causes: These can be further categorized into:
- Vasovagal syncope: caused by emotional or orthostatic stress 3.
- Situational syncope: caused by specific situational stressors 3.
- Carotid sinus syncope: caused by pressure on the carotid sinus, such as during shaving or wearing a tight collar 3.
- Atypical reflex syncope: episodes of syncope or reflex syncope that cannot be attributed to a specific trigger or syncope with an atypical presentation 3.
- Orthostatic causes: These are caused by an abnormal drop in systolic blood pressure upon standing, and can be due to autonomic nervous system failure or hypovolaemia 3, 4.
Mechanisms of Syncope
The immediate cause of syncope is cerebral hypoperfusion, which may occur due to:
- Systemic vasodilation
- Decreased cardiac output
- Both systemic vasodilation and decreased cardiac output 4. The primary objective of evaluating a patient with syncope is to identify the underlying cause and quantify the risk to the patient, which depends on the underlying disease rather than the mechanism of the syncope 3, 5.
Risk Stratification
Risk stratification is important in determining the need for hospitalization and guiding further evaluation and management 4, 5, 6. The Canadian Syncope Risk Score is one example of a risk stratification tool that may be beneficial in this decision 4.