Syncope
Overview
Syncope is a symptom of losing consciousness due to a temporary reduction in blood flow to the entire brain, and usually recovers spontaneously within seconds to minutes. It is not simply a symptom but can be a sign of various underlying diseases, so accurate evaluation is necessary; in particular, cardiogenic syncope may be associated with risk of sudden death.
Main Content
Definition and Pathophysiology
Syncope is a state of loss of consciousness caused by a sudden decrease in cerebral perfusion pressure. Normally, cerebral blood flow is maintained by autoregulatory mechanisms, but when mean arterial pressure drops due to decreased cardiac output or a sudden fall in systemic vascular resistance, cerebral blood flow cannot be sufficiently maintained. This leads to impairment of brainstem functions important for maintaining consciousness, such as the reticular activating system, resulting in syncope. Upon recovery, blood pressure rises again and cerebral perfusion resumes, restoring consciousness.
Classification of Causes
The causes of syncope are largely classified into three categories.
1. Reflex syncope (neurally mediated)
The most common type, including vasovagal syncope, situational syncope (coughing, urination, defecation, etc.), and carotid sinus hypersensitivity. Exaggeration of the vagal reflex causes bradycardia and vasodilation, leading to a drop in blood pressure and syncope.
2. Orthostatic hypotensive syncope
Occurs when blood pressure abnormally falls upon standing. Autonomic nervous system disorders, medications (diuretics, antihypertensives, etc.), dehydration, aging, and Parkinson's disease can be causes. It is significant when systolic blood pressure drops by 20 mmHg or more, or diastolic blood pressure by 10 mmHg or more, after a postural change.
3. Cardiogenic syncope
Caused by a sudden decrease in cardiac output due to arrhythmias (bradycardia, tachycardia, QT prolongation, etc.) or structural heart disease (aortic stenosis, cardiomyopathy, pulmonary embolism, etc.). This is the most dangerous type and should be suspected in cases of recurrent syncope, syncope during exercise, or a family history.
Clinical Manifestations and Prodromal Symptoms
Before syncope, prodromal symptoms such as dizziness, blurred vision, tinnitus, cold sweats, pallor, and nausea may appear. Reflex syncope usually occurs while standing, and there are cases where it can be avoided if the patient feels discomfort in advance and sinks down. Cardiogenic syncope occurs suddenly and often has few prodromal symptoms; especially when it occurs during exercise or in a lying position, it is a warning sign.
Diagnostic Approach
History taking is the most important part of diagnosing syncope. The situation of onset, posture, duration, recovery pattern, accompanying symptoms, medications, underlying diseases, and family history are carefully checked. Physical examination includes blood pressure (in both arms and upon standing), cardiac auscultation, and neurological evaluation. A 12-lead electrocardiogram is essential as a basic test, and if necessary, 24-hour Holter monitoring or an implantable loop recorder can be used to monitor cardiac rhythm over a long period. Carotid sinus massage, tilt table testing, echocardiography, and cardiac electrophysiological studies are also used to identify the cause.
Treatment and Management
Treatment depends on the cause.
- Reflex syncope: Patient education, increased fluid and salt intake, compression stockings, and avoidance of situations that trigger vasovagal syncope are basic. If bradycardia is frequent, pacemaker implantation can be considered, and drugs such as vasoconstrictors or fludrocortisone may be used.
- Orthostatic hypotension: Adjustment of causative medications, correction of dehydration, moving slowly upon standing, elevating the head during sleep, and use of pressor agents such as midodrine.
- Cardiogenic syncope: Antiarrhythmic drugs, catheter ablation, pacemakers, and implantable cardioverter-defibrillators (ICD) may be needed for arrhythmias, and surgical treatment may be required for structural heart disease.
Prognosis and Complications
Reflex syncope and orthostatic syncope generally have good prognoses, but trauma from falls (fractures, head injuries) can be problematic. In cardiogenic syncope, prognosis is determined by the severity of the underlying disease; syncope due to ventricular arrhythmias in particular can lead to sudden cardiac arrest, so prompt diagnosis and treatment are essential.
Recent Trends
As of 2024–2025, there are several notable changes in the diagnosis and management of syncope. First, advances in wearable devices (smartwatches, patch-type sensors) have made detection of pre-syncopal symptoms and ECG monitoring possible in daily life. This is greatly helping to identify the cause in patients with unexplained syncope. Second, genomic research has discovered new genetic variants associated with inherited arrhythmia syndromes and autonomic nervous system abnormalities, which are expected to serve as a basis for personalized treatment in the future. Third, AI-based prediction models for risk stratification of syncope patients have been developed and are being used in emergency departments to screen high-risk patients and reduce unnecessary hospital admissions. In addition, clinical research on new treatments such as neuromodulation for regulating the autonomic nervous system is actively underway.
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