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Posts Tagged ‘mechanism of syncope’

Recently , I came across a   young women  who underwent the following three tests for one episode of syncope after witnessing her pet dog bleeding with  an Injury !

  1. Carotid doppler
  2. Holter monitoring and event monitors
  3. Brain MRI /MR angiogram

This was followed up  by Head up tilt(HUT)  in a premier hospital

After 1 week of investigation ,a diagnosis of  Neurocardiogenic syncope was made and she was reassured and no drugs were prescribed.

(The collective yield of the above three investigation in fixing  a specific diagnosis is  less than 10 % of all known causes of syncope )

Syncope  approach  evaluation

To diagnose  common syncope . . . we need common sense !

Syncope is a dramatic  symptom.It is one of the commonest symptom in ER as well . Life time incidence of syncope is at least one episode in 50% all human life ! The definition  of syncope until recently , was liberal .Any transient loss of consciousness with spontaneous recovery  was termed syncope.

This includes

  1. Hypoglycemia
  2. Anemia
  3. Siezure disorders
  4. Structural  neurogenic (Including ,  brain tumors , Dural hematomas etc )
  5. Panic attacks (psychogenic)

Cardiologists wanted to fix syncope as an exclusive disorder of  circulatory insufficiency.By bringing in a modification in the definition  , ie  syncope is  now defined as a transient loss of consciousness due to   reduction in cerebral perfusion  .

This definition helped cardiologists  to exclude the above entities . Still many would include all in single basket as patient should be seen as a whole and we can’t expect them to  land according to our convenience and classification.

Here is an incomplete* list about causes of  syncope (* 99% complete ?)

Vascular

  • Vaso- vagal syncope in young ( Neuro-cardiogenic , Common , Benign)
  • Autonomic dysfunction of elderly ( Including postural hypotension )

Cardiac

Arrhythmic ( Sinus node dysfunction /CHB/Idiopathic VT/Long QT syndromes)

Structural heart disease

  • Valvular  heart disease  (LVOT/RVOT obstructions)
  • Myocardial disease
  • Rarely ischemic heart disease

Miscellaneous

  • Severe pulmonary hypertension (Including PPH ,  pulmonary Embolism )
  • Paradoxical embolism.
  • Aortic arch disease -Takayasu related arteritis .

Investigation

We have a sophisticated array  of investigation for syncope .It can be a never ending exercise , ranging from  spinal cord evoked potentials to diagnose Shy-drager syndrome ,   . . .  to implanting long-term loop recorders to decode  heart beat behavior.

However , evaluation of syncope is the ultimate wake-up call  to all current generation cardiologists  . . . Why clinical cardiology  should  never  be allowed to die (and  it  will not ! )

Common sense begins with answering  few simple questions . Is it really syncope ?

If  you ask this question three times and with  specific leads to the patient  and the witness ,  truth will come out  . 90% of times it may not be syncope at all (Near syncope, accidental  fall, dizziness ,extreme blurred vision, drowsiness  etc)

If it is syncope , Is there a non cardiac cause ?

It may related to the Hypoglycemia / Anemia /Panic attacks.Get a neurologist opinion , it would be terrible mistake if you miss a space occupying lesion  within the brain. (Missing chronic silent sub dural hematomas is  frequent   in the evaluation of syncope of elderly !)

Ruling out  cardiac syncope is relatively easy

In the remaining  patients  basic investigation like routine blood tests,ECG, ECHO   will help us  rule out most serious cardiac disorders.Similarly  bulk of the electrical cardiac syncope can be diagnosed.(Holter , carotid study in selected few )

Need for neurologist -cardiologist interaction.

Syncope due to VBI,  transient Ischemia attack , Senile vascular dementia  is a grey zone . Many have complex neuronal -vascular mechanisms . What is Consciousness ?  and  What is LOC ?  :Is it the lack of blood or severely depressed nerve signal in the reticular activating system? Lots of interaction between cardiologist and neurologist is required to clear our ignorance.(I  have one such  elderly patient who is intermittently awake ! I call this chronic syncope !)  .

Undiagnosed syncope is not  a crime

Realise the most important lesson in Medicine . If you  have ruled out all serious  causes of syncope you should have the courage to be satisfied with that !

Scientific pursuits has a limit. Searching for the mechanism of a psychogenic  fainting attacks with intra cerebral electrodes is a clear case of  physician acquiring a psychotic  behavior !

Final message

Syncope is not only a dramatic symptom for the patient , it also unfolds a drama of costly  investigations  . .  . many  with  dubious value.

Talk to the patient personally for  10 minutes in a quiet room, try to apply that elusive  clinical sense  . . .   it would rarely let you down !

After thought

What is the true clinical value of * Head up tilt Test (HUT)?

Will be posted soon

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The commonest cause of syncope is the neuro-cardiogenic or vasovagal syncope .

The following is  the possible neural  circuit  of this syncope . In fact . it is a  “Neuro -vascular circuit”

The afferent* (Two components  are present  -Both trigger sympathetic signal )

  1. Sympathetic (Prodrome /Anxiety /fear )
  2. Cardiac mechano /stetch receptors  located mainly in LV .(Can be in Aorta/Carotid )

* In some cases sensors  and afferent can be same entities.

The centre – Medullary Nucleus ambiguous /Tractus solitarius

The efferent -Strong parasympathetic overshoot and sympathetic withdrawal

Parasympathetic excess lead to bradycardia primarily, while sympathetic  withdrawal lead to

hypotension

Syncope recovery

As patient recumbent posture ; LV gets filled and  LV mechanoreceptors are passified .

Final message

The exact pathophysiologic basis of this syncope  still  not elucidated.But one thing is clear , the syncope is due to sympatho- parasympatho signal mismatch( and sort of a rivalry reaction)  !In this neural game , heart’s behavior is all the more funny , it initiates the reflex  while  the brain stem  “Boomerangs” it back to heart and vascular system ,  with a vagal onslaught .

To call this  simply as vasovagal  is not proper , that is why neuro -cardiogenic syncope was used.

Ideal terminology  would be  to call it as  cardio -neuro -cardiac syncope   as the cardiac component form the afferent limb as well as the efferent (target organ )

Reference

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