Syncope and Presyncope Mechanisms

• Syncope is a sudden loss of consciousness due to reduced cerebral perfusion.
• Presyncope is lightheadedness.
• Dizziness and presyncope are common in older age.

Mechanisms Underlying Presyncope or Syncope

• Cardiac syncope can be caused by mechanical cardiac dysfunction or arrhythmia
• Neurocardiogenic syncope (vasovagal or reflex syncope) occurs when an abnormal autonomic reflex causes bradycardia and/or hypotension.
• Postural hypotension results from impaired physiological peripheral vasoconstriction on standing, leading to hypotension.

Mechanism Bezold-Jarisch Reflex (Mechanism of VVS)

• Vasovagal syncope mechanism involves decreased venous return to the heart from prolonged standing.
• This leads to sympathetic stimulation as a compensatory mechanism, resulting in abnormal contraction of underfilled ventricles.
• Tachycardia then occurs, stimulating cardiac mechanoreceptors.
• This stimulation is mediated via the vagus nerve, leading to hypotension (vasodepressor response) and bradycardia (cardiac inhibitory response), which is key to diagnosing VVS.
• This whole process constitutes the Bezold-Jarisch reflex.

Causes of Syncope

• Cardiac syncope
• Neural mediated-Vasovagal or hypotension syncope
• Psychogenic syncope
• Neurological disease or seizure
• Hypoglycemia

Other types of syncope

• Situational syncope, like coughing or micturition syncope.
• Carotid sinus syncope
• Orthostatic Hypotension, a sudden drop of BP on standing from a static posture; several causes
• Drug-induced
• Fluid or blood loss
• Varicose veins (pooling of blood in legs upon standing)
• Autonomic dysfunction as in diabetes mellitus (DM
• Neurological diseases like transient ischemic attacks (TIA) or stroke.

Typical Features of Cardiac Syncope, Neurocardiogenic Syncope and Seizures

• Cardiac syncope can cause convulsions by inducing cerebral anoxia.
• Premonitory Symptoms for Cardiac syncope includes lightheadedness, palpitation, chest pain, and breathlessness.
• Premonitory Symptoms for Neurocardiogenic syncope includes nausea, lightheadedness, and sweating.
• Premontory Symptoms for Seizures includes delirium, hyperexcitabilty, and olfactory hallucination
• The unconscious period for cardiac syncope causes extreme 'death-like' pallor
• The unconscious period for neurocardiogenic syncope includes pallor
• The unconscious period for seizures include motor seizure activity, tongue-biting, urinary incontinence and is prolonged (> 1 min)
• Recovery for cardiac syncope includes flushing and is rapid (<1 min)
• Recovery for neurocardiogenic syncope includes nausea, and lightheadedness and is slow.
• Recovery for Seizures includes focal neurological signs, headache, prolonged delrium (> 5 mins)

Differentiating Seizures from Syncope

• Aura (e.g. olfactory) is present in seizures but absent in syncope.
• Cyanosis occurs in seizures but not in syncope.
• Lateral tongue-biting may occur in seizures.
• Post-ictal delirium, amnesia, and headache are characteristic of seizures.
• Rapid recovery is typical in syncope.

Diagnosis

• It's important to consider the patient history, conduct a physical examination, and perform necessary investigations.

Treatment

• No information provided

Syncope is a sudden loss of consciousness due to reduced cerebral perfusion while presyncope is lightheadedness. Cardiac syncope, neurocardiogenic syncope, and postural hypotension are common causes. The Bezold-Jarisch reflex explains vasovagal syncope involving decreased venous return and sympathetic stimulation.