What are the causes of syncope (fainting)?

From the Guidelines

Syncope is primarily caused by cerebral hypoperfusion, which can be due to various factors including vasovagal reactions, orthostatic hypotension, cardiac arrhythmias, or structural heart disease, as stated in the 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope 1. The causes of syncope can be broadly categorized into cardiac and noncardiac causes. Cardiac causes include bradycardia, tachycardia, or hypotension due to low cardiac index, blood flow obstruction, vasodilatation, or acute vascular dissection 1. Noncardiac causes include reflex syncope, orthostatic hypotension, volume depletion, dehydration, and blood loss 1. Some specific conditions that can cause syncope include:

• Vasovagal syncope (VVS), which is the most common form of reflex syncope, mediated by the vasovagal reflex 1
• Orthostatic hypotension (OH), which is a drop in systolic BP of $20 mm Hg or diastolic BP of $10 mm Hg with assumption of an upright posture 1
• Cardiac tamponade, constrictive pericarditis, and pulmonary embolus, which are all cardiovascular conditions that can lead to syncope 1
• Neurogenic orthostatic hypotension, which is a subtype of OH due to dysfunction of the autonomic nervous system 1
• Carotid sinus syndrome, which is reflex syncope associated with carotid sinus hypersensitivity 1 It is essential to identify the underlying cause of syncope, as it can have significant implications for treatment and management. According to the 2017 ACC/AHA/HRS guideline, any first-time syncope episode warrants medical evaluation to rule out serious cardiac causes, especially in older adults or those with heart disease risk factors 1.

From the Research

Causes of Syncope

The causes of syncope can be categorized into several types, including:

• Cardiac syncope: caused by cardiac disorders such as bradyarrhythmias or tachyarrhythmias 2
• Orthostatic hypotension: caused by an abnormal drop in systolic blood pressure upon standing, often due to autonomic nervous system failure or hypovolaemia 3, 4
• Reflex (neurally mediated) syncope: includes vasovagal syncope, situational syncope, carotid sinus syncope, and atypical reflex syncope 3, 4
• Neurocardiogenic syncopes: include vasovagal syncope, carotid sinus syndrome, orthostatic hypotension, and event-induced syncope 5

Specific Causes of Syncope

Some specific causes of syncope include:

• Cardiogenic syncopes: associated with cardiac diseases such as aortic stenosis, hypertrophic cardiomyopathy, atrial myxoma, myocardial infarction, pulmonary embolism, and cardiac tamponade 5
• Cardiac arrhythmias: such as ventricular tachycardia, supraventricular tachycardia, sinus bradycardia, and atrioventricular block 5
• Valvular heart disease, cardiomyopathies, and arrhythmias: which can be life-threatening causes of syncope 4

Diagnosis and Evaluation

Diagnosis and evaluation of syncope typically involve:

• History-taking and physical examination 3, 5, 6
• Noninvasive studies such as standard ECG, exercise testing, carotid sinus compression, Holter monitoring, tilt testing, and signal-averaged ECG 5, 6
• Further evaluation and testing as needed to determine the underlying cause of syncope 3, 2, 4, 6