What are the causes of syncope?

From the Guidelines

Syncope is primarily caused by cardiac conditions, reflex mechanisms, and orthostatic hypotension, with cardiac causes involving heart rhythm disturbances and structural heart problems, reflex-mediated syncope including vasovagal syncope, situational syncope, and carotid sinus syncope, and orthostatic hypotension resulting from dehydration, blood loss, or autonomic nervous system disorders, as stated in the 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope 1. The main causes of syncope can be categorized into:

• Cardiac causes, including heart rhythm disturbances such as bradycardia, tachycardia, or heart blocks, as well as structural heart problems like aortic stenosis, hypertrophic cardiomyopathy, or pulmonary embolism that obstruct blood flow 1
• Reflex-mediated syncope, including vasovagal syncope, situational syncope, and carotid sinus syncope, which are triggered by various factors such as emotional stress, pain, or pressure on the carotid artery 1
• Orthostatic hypotension, which occurs when blood pressure drops upon standing, often due to dehydration, blood loss, medications, or autonomic nervous system disorders 1 Other less common causes of syncope include neurological conditions, metabolic disorders, and psychiatric factors, which should be considered in the evaluation and management of patients with syncope 1. It is essential to identify the specific cause of syncope to provide proper treatment, which may include medication adjustments, lifestyle changes, or cardiac interventions depending on the underlying mechanism, as emphasized in the 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope 1.

From the Research

Causes of Syncope

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

• Cardiac syncope: caused by cardiac conditions such as structural heart disease, ischemic heart disease, or arrhythmias 2, 3
• Reflex (neurogenic) syncope: includes vasovagal syncope, which is the most common type of syncope, accounting for approximately 50% of cases 2
• Orthostatic hypotension: caused by a sudden drop in blood pressure when standing up, accounting for around 7% of syncope cases 2

Risk Factors and Diagnostic Approaches

Risk factors for syncope include:

• Structural heart disease
• Heart failure
• Family history of sudden death
• Abnormal electrocardiographic findings
• Ischemic heart disease and hypotension 2, 4, 3 Diagnostic approaches to syncope involve:
• Careful history taking to capture preceding situations, prodromal symptoms, and symptoms after syncope
• Physical examination, including orthostatic blood pressure measurements
• Electrocardiographic results
• Additional testing, such as prolonged electrocardiographic monitoring, stress testing, and echocardiography, may be considered in patients with cardiac syncope or those at higher risk of adverse outcomes 2, 4, 3, 5, 6

Diagnostic Tools and Techniques

Diagnostic tools and techniques used to evaluate syncope include:

• Implantable loop recorders, which can establish a diagnosis in 30-40% of patients over 2-3 years 2, 6
• Tilt table testing
• Risk stratification tools, such as the Canadian Syncope Risk Score, to inform decisions regarding hospital admission 3