From the Guidelines
Syncope is primarily caused by cerebral hypoperfusion, which can be attributed to various factors including cardiac issues, neurally mediated syncope, orthostatic hypotension, and noncardiac causes such as reflex syncope, volume depletion, dehydration, and blood loss. The causes of syncope can be broadly categorized into cardiac and noncardiac syncope. Cardiac syncope is caused by bradycardia, tachycardia, or hypotension due to low cardiac index, blood flow obstruction, vasodilatation, or acute vascular dissection 1. Noncardiac syncope, on the other hand, includes reflex syncope, orthostatic hypotension, volume depletion, dehydration, and blood loss.
Cardiac Syncope
Cardiac syncope can be caused by various conditions, including:
- Bradycardia
- Tachycardia
- Low cardiac index
- Blood flow obstruction
- Vasodilatation
- Acute vascular dissection
Noncardiac Syncope
Noncardiac syncope can be caused by:
- Reflex syncope, which includes vasovagal syncope and carotid sinus syndrome
- Orthostatic hypotension, which can be further classified into neurogenic OH and non-neurogenic OH
- Volume depletion
- Dehydration
- Blood loss
Reflex Syncope
Reflex syncope is a type of noncardiac syncope that is caused by a reflex that leads to vasodilation, bradycardia, or both. The most common form of reflex syncope is vasovagal syncope, which is characterized by diaphoresis, warmth, nausea, and pallor, and is often preceded by identifiable triggers or a characteristic prodrome 1.
Orthostatic Hypotension
Orthostatic hypotension is a condition characterized by a drop in systolic blood pressure of ≥20 mm Hg or diastolic blood pressure of ≥10 mm Hg within 3 minutes of assuming an upright posture. It can be caused by various factors, including dehydration, medication side effects, and autonomic dysfunction 1.
In clinical practice, it is essential to evaluate patients with syncope to determine the underlying cause, as some cardiac causes can be life-threatening. Treatment depends on identifying and addressing the specific cause, which may involve medication adjustments, lifestyle changes, or in some cases, implantable devices like pacemakers for cardiac-related syncope. The diagnosis of syncope is made primarily on the basis of a thorough history, physical examination, and eyewitness observation, if available 1.
From the Research
Causes of Syncope
The causes of syncope can be categorized into several types, including:
- Cardiac syncope: directly related to a cardiac disorder, with arrhythmias being the most common cause 2
- Arrhythmic syncope: a type of cardiac syncope specifically due to rhythm disorders, which can be caused by both bradyarrhythmia and tachyarrhythmia 2
- Reflex syncope: includes vasovagal syncope, situational syncope, carotid sinus syncope, and atypical reflex syncope 3
- Orthostatic syncope: caused by an abnormal drop in systolic blood pressure upon standing, often due to autonomic nervous system failure or hypovolaemia 3
- Neuromediated syncope: accounts for almost one third of cases, with vasovagal syncope common in young subjects and carotid sinus hypersensitivity common in the elderly 4
Specific Causes
Some specific causes of syncope include:
- Bradyarrhythmia: often treated with pacemaker implantation 4
- Ventricular arrhythmias: require the implantation of a defibrillator device 4
- Structural heart disease: may require specialist opinion and correction of the underlying problem 3
- Channelopathies: require a thorough approach to syncope work-up and management 2
Diagnostic Approach
The diagnostic approach to syncope depends on the clinical characteristics of the patient, risk stratification, and the suspected underlying cause 2, 3, 5, 4, 6