Page 167 - ILAE_Lectures_2015

Orthostatic syncope
Orthostatic syncope is caused by autonomic failure rather than an exaggerated and
inappropriate but essentially normal physiological response, as seen in neurocardiogenic
syncope. Patients lose the normal vasoconstrictor response to standing, resulting in venous
pooling and a postural fall in blood pressure, usually within seconds or minutes of becoming
upright. Unlike in neurocardiogenic syncope, the skin stays warm and well perfused, the pulse
rate is unchanged and sweating is absent. The causes of autonomic dysfunction are varied
and include autonomic neuropathy due to diabetes, alcohol, amyloidosis, genetic
abnormalities or complex autonomic failure, such as primary autonomic failure or multiple
system atrophy. Medications such as antihypertensives, phenothiazines, tricyclic
antidepressants, diuretics and medication for Parkinson’s disease may also be implicated.

Postural orthostatic tachycardia syndrome
Postural orthostatic tachycardia syndrome (POTS) is an autonomic disturbance characterised
by symptoms of orthostatic intolerance, mainly light-headedness, fatigue, sweating, tremor,
anxiety, palpitation, exercise intolerance and syncope or presyncope on upright posture19.
Patients also have a heart rate greater than 120 beats per minute on standing or an increase in
heart rate of 30 beats per minute from a resting heart rate after standing for 15 minutes,
compared to an increase of only 15 beats per minute in heart rate in the first minute of standing
in normal subjects. POTS is most common in females between the ages of 12 and 50 years
and may follow surgery, pregnancy, sepsis or trauma20. The pathophysiological basis of
POTS is not well understood. Hypotheses include impaired vascular innervation,
baroreceptor dysfunction and high plasma noradrenalin concentrations, of which impaired
innervation of the veins or their response to sympathetic stimulation is probably the most
important21.

Carotid sinus hypersensitivity
Carotid sinus hypersensitivity (CSH) is an exaggerated response to carotid sinus baroreceptor
stimulation. Even mild stimulation to the neck results in presyncopal symptoms or syncope
from marked bradycardia and a drop in blood pressure causing transiently reduced cerebral
perfusion. CSH is found in 0.59.0% of patients with recurrent syncope and is observed in
up to 14% of elderly nursing home patients and 30% of elderly patients with unexplained
syncope and drop attacks22,23. It is more common in males. It is associated with an increased
risk of falls, drop attacks, bodily injuries, and fractures in elderly patients but rates of total
mortality, sudden death, myocardial infarction, or stroke are similar to the general population.
Around 30% of cases are classified as cardioinhibitory where the predominant manifestations
are sinus bradycardia, atrioventricular block, or asystole due to vagal action on sinus and
atrioventricular nodes. Permanent pacemaker implantation is effective at reducing recurrence
rate24. The vasodepressor type also comprises 30% of cases and results in a marked decrease
in vasomotor tone without a change in heart rate. The remaining patients are of a mixed type25.
Untreated symptomatic patients have a syncope recurrence rate as high as 62% within four
years. The diagnosis is established by performing carotid sinus massage with the patient
supine, under ECG and blood pressure monitoring.

Cardiogenic syncope
Cardiogenic syncope arises from either a rhythm disturbance or structural cardiac defects.
The identification of a cardiac cause of syncope is of paramount importance because the
prognosis is poor if untreated10,13,26,27. A family history of sudden cardiac death may be
present, indicating the possibility of Brugada syndrome, long-QT syndrome or an inherited
cardiomyopathy, for example, hypertrophic cardiomyopathy, familial dilated
cardiomyopathy or arrhythmogenic right ventricular dysplasia. Typically, presyncopal
symptoms will be absent, and the circumstances of the syncope may be important. Syncope
after exercise is a manifestation of neurocardiogenic syncope, whereas syncope during