Classification and causes
Syncopal states are divided into several groups depending on the factor that led to the drop in cerebral blood flow:
- Neurogenic (reflex). The largest group. They develop due to inadequate vascular responses—marked peripheral vasodilation and a drop in blood pressure. This includes vasovagal syncope (up to 90% of all neurogenic cases), which is triggered by pain, the sight of blood, heat, or fatigue. Carotid sinus syncope is also distinguished, occurring in elderly men upon stimulation of the carotid sinus (tight collar, shaving, head tilting).
- Situational. Triggered by a specific action: severe coughing (cough syncope), straining during defecation or nighttime urination (often in men with prostatic hyperplasia), as well as intense physical exertion.
- Orthostatic. Associated with a rapid transition to an upright position. Causes: antihypertensive medications, hypovolemia (vomiting, blood loss), or autonomic failure in diabetes and Parkinson's disease.
- Cardiogenic. Caused by a sharp drop in cardiac output against the background of arrhythmias (AV block, tachycardia) or structural abnormalities (valve stenosis, myocardial infarction).
- Cerebrovascular. Occur during transient ischemic attacks in the vertebrobasilar basin.
- Dysmorphic and psychogenic. Triggered by hypoglycemia, anemia, or hyperventilation associated with anxiety disorders (hypocapnia causes cerebral vasospasm).
Clinical presentation
Most syncopal states are characterized by a stereotyped pattern of development. Loss of consciousness occurs rapidly—instantaneously or within a couple of dozen seconds.
At the moment of the attack, the patient slumps, resulting in a "soft" fall due to pronounced muscular atonia. Objectively, during this period, the following are observed:
- A sharp drop in systolic blood pressure (often below 60 mm Hg).
- Weakening of the pulse and respiratory movements.
- Pupillary dilation (mydriasis) and sluggish reaction to light.
The duration of the syncope itself varies from a few seconds to several minutes. Immediately upon regaining consciousness (post-syncopal period), the person looks very pale, the pulse remains weak, and arterial hypotension is recorded. Nausea and general weakness may persist for some time.
Diagnostic approaches
The cornerstone of syncope diagnostics is a detailed medical history taking. It is extremely important for the physician to know the patient's position, what they were doing before the fall, and what medications they take regularly. Electrocardiography (ECG) is performed absolutely universally to rule out life-threatening cardiogenic causes.
To clarify the type of syncope, provocative tests are used:
- Orthostatic test: the patient is moved from a horizontal to an upright position. The diagnosis is confirmed if systolic blood pressure drops by 20 mm Hg or more.
- Carotid sinus massage: performed only after ruling out carotid artery atherosclerosis. Blood pressure drop and the presence of asystole are assessed.
- Hyperventilation test: deep and frequent breathing for 3–5 minutes to reveal psychogenic (anxiety) attacks.
If the cause remains unclear, Holter monitoring, echocardiography (EchoCG), and blood tests are prescribed to check for anemia or hypoglycemia.
Emergency Medicine
When a pre-syncopal state develops, the person must be immediately laid down or seated, with their head and torso tilted forward as much as possible to gravitationally ensure blood flow to the head.
If syncope has already occurred, the algorithm is as follows:
- Lay the victim flat on their back on a firm surface.
- Be sure to elevate the legs to increase venous return to the heart.
- Unbutton the collar, remove the tie—remove anything compressing the neck and chest.
- For reflex stimulation, you can spray the face with cold water, place a cold towel on the forehead, or let them inhale ammonia vapors.
After the patient regains consciousness, they must not get up immediately—they should lie down for another 10–15 minutes to avoid orthostatic collapse.
Briefly: answers to topical questions
What neurodegenerative and endocrine diseases lead to orthostatic syncope due to autonomic failure?
Orthostatic syncope due to autonomic failure is caused by the following neurodegenerative and endocrine pathologies.
- Parkinson's disease is a neurodegenerative disorder accompanied by autonomic failure.
- Dementia with Lewy bodies is a neurodegenerative disorder characterized by frequent manifestations of orthostatic hypotension.
- Diabetes mellitus is an endocrine disease that causes autonomic neuropathy.
Internal organ amyloidosis and renal failure can also cause orthostatic syncope.
What structural cardiovascular pathologies can cause cardiogenic syncope?
The causes of cardiogenic syncope can include structural heart changes and conditions leading to reduced cardiac output:
- Aortic or mitral stenosis.
- Hypertrophic cardiomyopathy.
- Acute myocardial infarction.
- Atrial myxoma.
- Cardiac tamponade.
- Severe heart failure.
- Pulmonary embolism (PE).
What instrumental and provocative tests are used for the differential diagnosis of unexplained syncope?
For the differential diagnosis of unexplained syncope, the following are used:
- Electrocardiography (ECG).
- Holter ECG monitoring.
- Echocardiography (EchoCG).
- Intracardiac electrophysiological study (EPS)—performed prior to a tilt table test to rule out cardiac pathology.
- Orthostatic test (tilt table test)—to identify vasovagal causes and orthostatic hypotension.
- Carotid sinus massage—to identify carotid sinus syncope.
- Hyperventilation test—to identify hyperventilation attacks.
What specific ECG patterns and syndromes are predictors of life-threatening arrhythmogenic syncope?
Arrhythmogenic causes and syndromes associated with life-threatening syncope include:
- Brugada syndrome—a spontaneous type 1 ECG pattern combined with syncopal episodes.
- Long QT syndrome.
- Wolff–Parkinson–White syndrome.
- Sick sinus syndrome.
- Complete atrioventricular block.
Which pharmacological drug classes can provoke the development of orthostatic syncope?
Various pharmacological drug classes can provoke the development of orthostatic syncope and postural hypotension.
- Antihypertensive drugs are the most frequent cause (including diuretics and alpha-blockers).
- Vasodilators — short-acting and long-acting organic nitrates.
- Antiparkinsonian drugs — specifically, dopamine receptor agonists.
- Antidepressants — tricyclic antidepressants (e.g., amitriptyline).
- Psychotropic agents — hypnotics and sedatives.
The risk of drug-induced orthostatic syncope is particularly high in elderly patients.
First aid rule for syncope: "Head down, legs up." This simple action mechanically returns blood volume to the brain.
Class and exam questions
Which type of syncope is the most common?
Vasomotor (vasovagal) syncope is the most common. It accounts for up to 90% of all neurogenic syncopes, especially among young people.
How to identify cardiogenic syncope by symptoms?
Cardiogenic syncope is characterized by the absence or a very short duration of the pre-syncopal state. Before losing consciousness, a person may experience cardiac pain, palpitations, or shortness of breath.
Should I call an ambulance if the person recovers quickly?
If syncope occurs for the first time, is accompanied by chest pain, or happens in an elderly patient, a medical examination and ECG are mandatory to rule out myocardial infarction or fatal arrhythmias.
What else to study on this topic
- Pathogenesis of carotid sinus hypersensitivity syndrome
- Differential diagnosis of syncope and epileptic seizures
- Indications for Holter monitoring in unexplained syncope
- Drug-induced orthostatic hypotension in the elderly
- Syncope in transient ischemic attacks (vertebrobasilar system)
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