Makindo Medical Notes

Related Subjects: |Transient Loss of Consciousness |Vasovagal Syncope |Syncope |Aortic Stenosis |First Seizure |Carotid Sinus Syncope

Vasovagal syncope, or fainting, is a protective mechanism that helps restore cerebral blood flow by allowing the patient to fall, positioning the head and heart at the same level. Avoid preventing the fall, as this can worsen symptoms or delay recovery.

Physiology

• Normal standing causes blood to pool in the lower extremities due to gravity, reducing venous return to the heart.
• The baroreceptors in the carotid sinus and aortic arch sense the drop in blood pressure and activate the sympathetic nervous system.
• This leads to an increase in heart rate and contractility, as well as vasoconstriction, to maintain blood pressure and cardiac output.
• These mechanisms help maintain cerebral perfusion despite the effects of gravity.

Pathophysiology

• Vasovagal syncope occurs due to an abnormal reflex response involving the autonomic nervous system.
• The initial sympathetic response to standing is followed by an exaggerated activation of the parasympathetic (vagal) system.
• This leads to bradycardia (slow heart rate) and vasodilation (widening of blood vessels), causing a sudden drop in blood pressure and heart rate.
• As a result, cerebral perfusion falls below a critical threshold, leading to syncope (fainting).
• This response is known as the Bezold-Jarisch reflex, which is characterized by a paradoxical bradycardia and vasodilation in response to vigorous heart contractions, particularly when the heart is relatively empty.

Synonyms

• Neurocardiogenic syncope
• Simple faint
• Vagally mediated syncope
• Reflex syncope

Situational Triggers

• Carotid sinus syncope: Triggered by turning the head or applying pressure to the neck, such as during shaving. It is associated with carotid sinus hypersensitivity, particularly in older adults.
• Cough syncope: Occurs after a bout of coughing, more common in patients with obstructive airways disease.
• Micturition syncope: Often affects men, occurring during or immediately after urination, especially at night.
• After large meals, especially with alcohol, or in settings like a warm restaurant or pub.
• Standing in a warm environment, such as during religious services or in queues.
• Emotional stress or sight of blood.

Clinical Presentation

• Occurs across all age groups but is a common cause of syncope in the elderly.
• Typically triggered by factors like pain, fatigue, heat, prolonged standing, or sudden blood loss.
• Patients often describe a prodrome of buzzing in the ears, nausea, sweating, vision dimming, and pallor before fainting.
• Loss of muscle tone and consciousness causes the patient to fall.
• Jerking movements may occur during syncope, but these are not indicative of epilepsy.
• Tonic-clonic movements and urinary incontinence can occur, potentially leading to misdiagnosis as a seizure.

Tilt Test

• Head-Up Tilt Testing can help identify neurocardiogenic syncope. It involves using a tilt table to achieve a 60-degree angle for 45 minutes, monitoring ECG and BP continuously.
• Two main response types:
  • Vasodepressor: Significant drop in blood pressure (> 50 mmHg) with or without syncope. Treatment may include fludrocortisone, stopping diuretics, compression stockings, increased salt intake, beta-blockers, and SSRIs.
  • Cardioinhibitory: Significant bradycardia (heart rate < 40 bpm or pause > 3 seconds) before BP drops, leading to syncope. Treatment may include a pacemaker.

Any sudden loss of consciousness without warning must be assumed to be a cardiac arrhythmia until proven otherwise. It has implications for those who wish to drive. Patients must be advised not to drive until the diagnosis is confirmed, and they should inform the DVLA.

Differentials and Causes

• Cardiac Causes:
  • Arrhythmias: Profound bradycardia or tachycardia. Symptomatic palpitations can be a pointer but are not always present.
  • Structural heart issues: Aortic stenosis, hypertrophic cardiomyopathy, myocardial ischaemia, tamponade, or pulmonary embolism.
• Neurological Causes:
  • Seizures, strokes, or transient ischaemic attacks (TIA).
  • Jerky limb movements and incontinence can occur in prolonged vasovagal attacks, making it difficult to differentiate from epilepsy without a good eyewitness account.
• Metabolic Causes:
  • Hypoglycaemia, especially in patients with diabetes on insulin or sulfonylureas.
  • Rarely, insulinoma (a pancreatic tumour).
• Respiratory Causes: Hypoxaemia from underlying lung disease or high-altitude exposure.
• Drug-Induced: Alcohol, certain medications (e.g., nitrates, antihypertensives).
• Psychogenic Causes: Hyperventilation and panic attacks, which may present with lightheadedness, palpitations, chest discomfort, or numbness.
• Orthostatic Hypotension: Common in the elderly, especially with antihypertensive medications or in conditions like autonomic neuropathy or Parkinson's disease.

Management

• Reassurance and Education: Explain the benign nature of the condition to patients. Educate them on recognizing prodromal symptoms to prevent falls.
• Lifestyle Modifications:
  • Advise patients to avoid triggers such as prolonged standing, hot environments, or skipping meals.
  • Encourage adequate fluid intake and salt consumption if there are no contraindications (e.g., hypertension).
  • Teach physical counter-pressure maneuvers like leg crossing or tensing the leg muscles when they feel symptoms coming on.
• Pharmacological Management:
  • Fludrocortisone: Can be used to increase blood volume and improve blood pressure control.
  • Midodrine: An alpha-agonist that can help increase vascular tone.
  • SSRIs: May be useful in refractory cases, as they can modulate autonomic function.
  • Beta-blockers: Occasionally used in younger patients with a significant vasodepressor component.
• Pacing: Pacemakers may be indicated in patients with a significant cardioinhibitory response and recurrent, refractory syncope.
• Postural Training: Gradually increasing the time spent in an upright position can help patients adjust to standing and reduce episodes.

References

• European Society of Cardiology - Guidelines for the Diagnosis and Management of Syncope
• BMJ Best Practice - Syncope