Syncope

Syncope is a symptom, defined as a transient, self-limited loss of consciousness, usually leading to falling. The onset of syncope is relatively rapid, and the subsequent recovery is spontaneous, complete, and usually prompt. The underlying mechanism is a transient global cerebral
hypoperfusion.

Presyncope or ‘near-syncope’ refers to a condition in which patients feel as though syncope is imminent.

Non-syncopal conditions: Several disorders resemble syncope in two different ways. In some, consciousness is impaired or lost because of metabolic disorders (including hypoxia, hyperventilation, hypoglycaemia), epilepsy and intoxications. In several other disorders, consciousness is only apparently lost; this is the case in somatization disorders, cataplexy
and drop attacks.

Causes of syncope:

Neurally mediated ( reflex )

• Vasovagal syncope
  
• Carotid sinus hypersensitivity
• Situational syncope

Orthostatic Hypotension

• autonomic failure
• drug and alcohol induced
• volume depletion

Cardiac Arrhythmia

• Implanted device malfunction
• Sinus nodal dysfunction
• Atrioventricular conduction system disease
• Drug induced proarrhythmias
• Paroxysmal SVT and VT
• Inherited syndrome ( e.g., Brugada's syndrome, long QT syndrome )

Structural cardiac or cardiopulmonary disease

• Obstructive cardiac valvular disease
• Obstructive cardiomyopathy
• Myocardial infarction
• Atrial myxoma
• Acute aortic dissection
• Pericardial disease/tamponade
• Pulmonary embolism/pulmonary hypertension

Cerebrovascular

• vascular steal syndrome

Three key questions should be addressed during the initial evaluation:

• Is loss of consciousness attributable to syncope or not?
• Are there important clinical features in the history that suggest the diagnosis?
• Is heart disease present or absent?

Is loss of consciousness attributable to syncope or not?
Differentiating true syncope from other ‘non-syncopal’ conditions associated with real or apparent transient loss of consciousness is generally the first diagnostic challenge and influences the subsequent diagnostic strategy.

Are there important clinical features in the history that suggest the diagnosis?

PMH/o:

• Family history of sudden death, congenital arrhythmogenic heart disease or fainting
• Previous cardiac disease
• Neurological history (Parkinsonism, epilepsy, narcolepsy)
• Metabolic disorders (diabetes, etc.)
• Medication (antihypertensive, antianginal, antidepressant agent, antiarrhythmic, diuretics and QT prolonging agents

Pre-syncopal events:

• Position (supine, sitting or standing)
• Activity (rest, change in posture, during or after exercise, during or immediately after urination, defaecation, cough or swallowing);
• Predisposing factors (e.g. crowded or warm places, prolonged standing, post-prandial period) and of precipitating events (e.g. fear, intense pain, neck movements);
• Nausea, vomiting, abdominal discomfort, feeling of cold, sweating, aura, pain in neck or shoulders, blurred vision;
  

During syncope:

• Way of falling (slumping or keeling over),
  
• skin colour (pallor, cyanosis),
  
• duration of loss of consciousness, breathing pattern (snoring),
  
• movements (tonic, clonic, tonic-clonic or minimal myoclonus, automatism)

Post syncope:

• Autonomous symptoms - Nausea, vomiting, sweating
• confusion
• chest pain, palpitations
• urinary or faecal incontinence

Is heart disease present or absent?
The absence of suspected or certain heart disease excludes a cardiac cause of syncope with the exception of syncope accompanied by palpitations which could be due to paroxysmal tachycardia.

Conversely, the presence of heart disease at the initial evaluation is a strong predictor of cardiac cause of syncope and virtually includes all cardiac syncopes, but its specificity is low as about half of patients with heart disease have a non-cardiac cause of syncope.

Specificity increases in some situations. These are:

• In the presence of heart disease, some historical variables such as blurred vision, syncope occurring in the supine position or during effort, or convulsive syncope suggest a cardiac cause of syncope with high specificity. These patients should probably be hospitalized and cardiological examinations should be given priority.
• Even in the presence of heart disease, a long duration (>4 years) of symptoms, syncope preceeded by abdominal discomfort or followed by nausea and sweating suggest a neurally mediated cause of syncope with high specificity. In these cases autonomic tests should be given priority and, in case of their positivity, a neurally-mediated mechanism is likely and the diagnostic work-up should be stopped.

Further Reading: http://www.escardio.org/guidelines-surveys/esc-guidelines/Documents/SYNCOP/guidelines-syncope-ES-2001.pdf