Syncope is defined transient loss of consciousness due to transient loss of cerebral perfusion characterized by rapid in on set, short in duration with complete recovery
Syncope can occur because of cardiac and vascular causes.
Diseases like stroke, TIA, convulsions metabolic causes (hypoglycemia) some times mimic syncope (Note: - these are not syncopes) their prompt identification very important.
Syncope has bimodal incidence i.e. syncope is more common in age group of 10 to 30 years of age with peak at 15years, second peak is after 65 years of age after 75 years this incidence increases even further.
Classification of syncope by etiology
Divided into vascular and cardiac causes further these broad groups are divided as below
- Subclavian steel syndrome
- Autonomic neuropathy
- Volume depletion ( dehydration, blood loss , etc)
- Drugs and alcohol
- Reflex mediated
- Vasovagal syncope (neuro cardiogenic syncope)
- Carotid body hypersensitivity
- Situational syncope
- Obstructive valver heart diseases like AS PS Pulmonary embolisms
- Secondary to autonomic neuropathy like Bradbury-Eggleston syndrome, Shydragar syndrome, diabetes , Parkinson’s, old age
- Following standing from supine position around 800ml of blood is shifted in to abdomen and legs. This reduces cardiac output by decreasing preload, to compensate this, heart rate and contractility increases and peripheral vasoconstriction also occurs by increased sympathetic outflow, these reverse the falling Blood pressure in normal persons.
- In patients of orthostatic hypotension this composition is not adequate ,so blood pressure fall is not prevented.
- Orthostatic hypotension is defined as drop of systolic blood pressure more than 20mmhg and/or diastolic blood pressure more than 10mmhg on within 3mintes of standing.
- Unlike orthostatic hypotension in vasovagal syncope fall in BP is following prolonged standing in dry hot weather (here mechanism is different)
- Postural orthostatic tachycardia syndrome (POTS), is milder form of orthostatic intolerance, where heart rate increases more than 28beats/min from base line, but blood pressure change is not significant. patient have signs of syncope /presyncope.
- Other vascular and non reflex syncops manifest like orthostatic hypotension, but here cause is volume depletion or vasodilatation secondary to antihypertensive drugs
Reflex mediated syncope
- Following standing orthostatic tolerance is normal, syncope here is secondary trigger (induced reflex) which leads to sudden bradycardia or asystole and hypotension some time only hypotension without bradycardia
- There are two types of reflex mediated syncops. First one is Vasovagal syncope other is Carotid body hypersensitivity
- Vasovagal syncope (neurally mediated syncope) occurs following prolonged standing in dry hot weather leading to pooling of blood in lower limbs, this decreases preload to heart, leading decrease cardiac output, leading to increased level of catecholamine these stimulates heart to contract vigorously in a volume depleted heart. Now paradox occurs i.e. machano receptors located in wall of atria and ventricle are stimulated by vigarocity of contraction (in susceptible individual) leading sympathetic withdrawal and increase vegal tone, which manifest as bradycardia and hypotension and syncope occurs
- Vasovagal syncope can also occur by other reason, for example site of blood, here proposed mechanism is cerebral in origin
- Carotid body hypersensitivity is reflex mediated syncope. In approx one third of elderly patients barorecptors present at origin of internal carotid artery when stimulated induce syncope. If sinus pause more than 3secs present than patients needs dual chamber pacemaker.
Cardiac causes of syncope
- Bradyarrythmias by decreasing cardiac output induce syncope (AV Block, Sick Sinus syndrome etc)
- Techyarrythmias leads to decreased ventricle filling volume (decreased diastole interval) leading to decreased cardiac output leading syncope (VT, SVT)
- Structural causes of heart like Aortic stenosis, pulmonary stenosis, pulmonary embolism also cause by decreased cardiac output
cardiac causes of syncope are not associated with prodromal symptoms like neuro cardiogenic syncope
- HUTT test (Head up tilt test) is very important for diagnosing neurocardiogenic syncope (vasovagal syncope). In this test, person with recurrent syncope, after 20minites of supine position, is tilted to 70 degrees on a tilt table for 40mintes. Patient is monitored for induction of syncope, if not then this is augmented with drugs like isoprenaline or nitroglycerine. Response is reported as cardio inhibitory (here decrease in heart rate precede blood pressure fall) or Vasodepressive here fall in blood pressure occurs without decrease in heart rate or mixed where decrease in heart rate less and associated with Blood pressure fall.
- other test like EP study Echocardiography are done for diagnosing cardiac causes of syncope
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