Syncope

Syncope refers to the sudden and brief loss of consciousness and postural tone, followed by spontaneous recovery. It is a very common disorder at any age, generally benign and self-limiting, although it can also be an indicator of an underlying condition.

Symptoms

Syncope is preceded by a set of symptoms called presyncope, which may also occur without leading to a loss of consciousness. The most common symptoms are:

• Pallor
• Dizziness
• Narrowing of the visual field (tunnel vision)
• Heat
• Cold sweats
• Nausea
• Blurred vision
• Weak pulse
• Pupil dilation
• Shallow breathing
• Occasionally, involuntary muscle jerks

Causes

Syncope is caused by a decrease in cerebral arterial perfusion, meaning the blood flow to the brain. Depending on the cause of this decrease, the following types of syncope are classified:

• Neuromediated, autonomic, or reflex syncope: Caused by a transient dysfunction of the reflexes that control blood pressure and heart rate (the autonomic nervous system).
• Vasovagal or neurocardiogenic syncope: Triggered by certain stimuli, the heart rate slows down, and the blood vessels in the legs dilate. This causes blood to pool in the legs, lowering blood pressure, which reduces blood flow to the brain. This is the most common type. Common triggers include:
• Pain
• Heat
• Seeing or losing blood (venipuncture syncope)
• Nervousness, fear, or stress
• Orthostatic hypotension syncope: Blood pressure drops abruptly when standing up because, due to gravity, blood tends to stay in the legs and abdomen. This usually leads to presyncope without complete loss of consciousness. Sometimes, an underlying condition causes it, including:
• Dehydration
• Postprandial hypotension: Low blood pressure after eating
• Endocrine disorders like diabetes, adrenal insufficiency, or thyroid conditions
• Nervous system diseases like Parkinson's, amyloidosis, or multisystem atrophy
• Postural Orthostatic Tachycardia Syndrome (POTS): When standing, the heart rate increases, and blood pressure becomes unstable as a compensation for orthostatic hypotension. It is the main cause of exercise intolerance. It is common in adolescents and usually improves or disappears in the twenties. Its causes are unknown, but it often manifests after events like:
• Pregnancy
• Major surgery
• Trauma
• Viral illness
• Carotid sinus syncope: Caused by turning the head, looking up, tightening the collar of a shirt, or shaving.
• Situational syncope: Triggered by specific situations:
• Micturition (micturition syncope)
• Gastrointestinal stimulation: Swallowing (swallowing syncope), defecation (defecatory syncope), or abdominal pain
• Cough (cough syncope)
• Squeezing the eyes
• Hair combing or stretching
• Weightlifting
• Laughter
• Sudden cessation of physical activity
• Sobbing or apnea syncope: The most common type of syncope in children under four years of age, caused by involuntary breath-holding. There are two different manifestations:
• Triggered by a shock or mild pain. There is no crying or it is very brief. When losing consciousness, the child shows pallor, which may be accompanied by rigidity and muscle contractions.
• Triggered by strong emotions like anger or frustration. There is intense crying and bluish coloration upon loss of consciousness.
• Cardiogenic syncope: Originates from heart conditions, including:
• Disorders that cause arrhythmias, such as ventricular tachycardia, sinus node dysfunction, atrioventricular block, or supraventricular tachycardia
• Disorders causing myocardial dysfunction, such as myocarditis, Kawasaki disease, or dilated cardiomyopathy
• Disorders that cause obstruction of the ventricular outflow, like aortic stenosis, hypertrophic cardiomyopathy, or pulmonary hypertension
• Vascular disorders, like hypovolemia
• Metabolic syncope: Hypoglycemia, drug intake, or poisoning
• Other causes: Heat stroke, anaphylaxis

Risk Factors

Factors that increase the risk of syncope include:

• Anemia
• Fatigue, tiredness, or weakness
• Hypotension
• Cardiovascular disorders
• Intense physical activity
• Dehydration
• Emotional stress
• Certain medications, like beta-blockers, antihypertensives, antihistamines, antipsychotics, antidepressants, antiarrhythmics, among others
• Family history, especially with Postural Orthostatic Tachycardia Syndrome

Complications

Autonomic syncopes are benign and do not present complications by themselves, although fainting from loss of consciousness can lead to falls and trauma of varying severity. Cardiogenic syncopes, however, are a risk factor for sudden death, a sudden interruption of cardiac activity resulting in death within seconds.

Alarming signs suggesting a cardiac origin include:

• Syncope during exercise, with palpitations and chest pain
• Syncope at rest or in a lying position
• Seizures
• Family history of sudden death or heart disorders
• Multiple recurrences in a short period

Prevention

Staying hydrated helps prevent syncope. Additionally, loss of consciousness can be avoided by taking actions when presyncope symptoms begin:

• Take slow, deep breaths
• Lie down with legs elevated
• Sit with the head between the knees
• When standing, cross the legs and apply pressure
• Squeeze something soft with your hands
• Tense arms horizontally, with hands interlocked and elbows pulling outward

Which doctor treats syncope?

Syncope can be evaluated and treated by specialists in cardiology, family medicine, internal medicine, neurology, and pediatric neurology.