Physiology and Pathophysiology of Syncope

Question 1

Syncope

Answer 1

A specific form of transient loss of consciousness due to cerebral hypoperfusion, characterised by rapid onset, short duration and spontaneous recovery

Question 2

Types of syncope

Answer 2

Reflex, cardiac and orthostatic

Question 3

Transient Loss of Consciousness

Answer 3

A state of real or apparent loss of consciousness with loss of awareness, motor control. Short duration and results in amnesia

Question 4

Types of reflex syncope

Answer 4

Vasovagal
Situation
Carotid Sinus

Question 5

Causes of TLOC

Answer 5

Head trauma
Syncope
Epileptic seizure
TLOC mimics

Question 6

Initial evaluation of TLOC

Answer 6

History
Full physical examination
Orthostatic BP measurement
12-lead ECG

Question 7

Reflex syncope

Answer 7

All types of syncope in which neural reflexes modify HR (cardioinhibition) and/ or vascular tone (vasodepression), hence predisposing to a fall in MAP of sufficient severity to cause a transient period of cerebral hypoperfusion causing syncope/ near syncope

Question 8

Which type of syncope is the most common?

Answer 8

(vasovagal) reflex syncope

Question 9

What happens when reflex pathways are activated?

Answer 9

cardioinhibition via vagal stimulation-> bradycardia and decreased CO

Vasodepression via reduced sympathetic activity to blood vessels> decreased SVR, venous return, SV and CO

MAP decreases as CO and SVR falls-> cerebral hypoperfusion->syncope/ near syncope

Question 10

What triggers vasovagal reflex syncope?

Answer 10

emotional or orthostatic stress

Question 11

Symptoms of vasovagal reflex syncope

Answer 11

Typical prodrome (pallor, sweating, nausea)

Question 12

How to avoid vasovagal reflex syncope?

Answer 12

increase venous return by crossing legs or adopting horizontal gravity neutralisation position

Question 13

Risks of vasovagal reflex syncope

Answer 13

Injury when falling

* not associated with increased mortailtiy

Question 14

Treatment for vasovagal reflex syncope

Answer 14

education
reassurance
avoiding triggers
adequate hydration

Question 15

Situational reflex syncope

Answer 15

Faint during or immediately after a specific trigger eg coughing

Question 16

Treatment of situational reflex syncope

Answer 16

treatment of cause eg cough
lie down
hydrate
cardiac permanent pacing

Question 17

Carotid Sinus Reflex Syncope

Answer 17

Triggered by mechanical manipulation of neck, tight collar etc.

eg after head and neck surgery

Common in elderly (esp males)

Question 18

Associated condition of carotid sinus reflex syncope

Answer 18

Carotid artery atherosclerosis

Question 19

Treatment of carotid sinus reflex syncope

Answer 19

Permanent cardiac pacing

Question 20

Cause of postural/ orthostatic hypotension

Answer 20

Failure of baroreceptor responses to gravitational shifts in blood when moving from horizontal to vertical position

Question 21

Risk factors for postural hypotension

Answer 21

Age
Medication
Reduced intravascular volume
Prolonged bed rest

Question 22

Positive result for postural hypotension

Answer 22

Drop within 3mins of standing from lying position:-

• in SBP of at least 20mmHg (with or without symptoms)
• in DBP of at least 10mmHg (with symptoms)

Question 23

Symptoms of postural hypotension

Answer 23

Lightheadedness, dizziness, blurred vision, falls

Question 24

Cardiac syncope

Answer 24

Syncope caused by a cardiac event which results in a sudden drop in CO

Question 25

Causes of cardiac syncope

Answer 25

Arrhythmias Acute MI Structural cardiac disease Other CVD eg PE

Question 26

Features suggesting cardiac syncope

Answer 26

Presence of structural cardiac abnormality Family history of sudden death at a young age Palpitations followed by syncope Syncope during excretion or when supine