Syncope

Syncope is a transient loss of consciousness and muscle tone which occurs suddenly, and which resolves spontaneously due to a transient decrease in perfusion to the brain. Syncope is one of multiple causes of transient loss of consciousness (TLOC). The most common types of syncope are:

• Cardiac syncope
• Reflex syncope
  • Vasovagal syncope
  • Carotid sinus syndrome
• Orthostatic syncope

Cardiac syncope is a major risk factor for sudden cardiac death and so it should be ruled out in cases where another definite cause can’t be determined.

Etiology

Cardiac syncope occurs when the heart is suddenly unable to provide enough perfusion for the brain. This can either be due to an arrhythmia or due to a structural obstruction of the outflow tract of the heart. This type of syncope accounts for only 10% of syncopes. This can be due to:

• Arrhythmia
  • Sick sinus syndrome
  • Supraventricular tachycardia
    • Atrial fibrillation with a fast ventricular rhythm
    • WPW syndrome
  • Ventricular tachycardia
  • AV block
• Structural outflow obstruction
  • Left ventricle hypertrophy
  • Hypertrophic cardiomyopathy
  • Aortic stenosis
  • Pulmonary embolism

Vasovagal syncope is the most common cause of syncope and occurs because of a stress trigger which stimulates the vagus nerve, causing an unproportionally large increase in parasympathetic activity, which decreases heart rate and blood pressure. This can occur due to strong pain, fear, a sight of blood, etc. More than 1/3 of people have experiences vasovagal syncope once.

Orthostatic hypotension occurs after standing up if the body can’t initiate the circulatory changes which maintains the blood pressure in the upright position. It occurs most commonly in patients taking antihypertensives.

Evaluation

A thorough history is essential. In patients taking antihypertensives and having low BP, orthostatic syncope is most likely. If syncope occurred after pain, a scare, etc., vasovagal syncope is most likely. The following features are suspicious for cardiac syncope:

• Occurring during exercise
• Occurring in supine position
• Patient has heart disease or is at high risk for it
• Family history of cardiac syncope or sudden cardiac death

If cardiac syncope can’t be reliably ruled out, they should be admitted to be evaluated. All patients should undergo ECG. Echocardiography can diagnose aortic stenosis and hypertrophy. D-dimer and possibly CTPA if PE is possible. If no abnormalities are detected, a Holter monitor may detect a paroxysmal arrhythmia.

An orthostatism test can be used if orthostatic syncope can’t be ruled out. The BP of the patient is measured while supine and after standing up at 0, 1, 3, and 5 minutes. A drop of SBP > 20 mmHg or development of symptoms is a positive test.

Treatment

Treatment depends on the underlying cause. Orthostatic syncope can be managed with instruction on not to stand up quickly and reduction in antihypertensive dose. Patients should also be instructed to adequately drink and eat salt.

• Afib can be controlled with medication
• WPW can be ablated
• SSS and bradyarrhythmias can be controlled with a pacemaker
• Vfib can be prevented with ICD
• HCMP can be treated with drugs and ICD