Posts Tagged ‘Hemodynamics’

Humans have roughly 5 to 6 liters of blood at any given time in their  body  . Out of  this*

50% (2500ml)  is located in the systemic venous compartment.
18% is within the pulmonary circulation participating in the vital oxygenation
12% (500-600ml) is within the cardiac chambers.
8%  is in the arterial tree of  the body.
5%  is  within the  capillaries.
2%  is in the aorta.
* Source : Best & Taylor Physiological basis of  medical practice 1966, 8th edition

What is the implication of this predominantly venous distribution of blood  at rest ?

  • A competent venous tone is essential  for the human beings to maintain the erect posture.
  • Bulk of the cause of syncope in humans is due to peripheral  mechanism like loss of vascular tone and resultant venous pooling.
  • The  concept of venous reservoir is so important in emergency situations like  hypotension  as  simple elevation of legs  is equivalent to  infusing 500 -800 ml of intravenous saline .
  • Similarly during acute left ventricular failure trunk elevation and legs dangling down can reduce the pulmonary congestion very significantly and reduce pulmonary capillary wedge pressure (LVEDP)

 Autonomic dysfunction and venous insufficiency

 Autonomic dysfunction and resultant  orthostatic hypotension is directly related  to venous reservoir dysfunction.Increasing effective circulatory volume by elastic stockings or administration of mineralocorticosteroids like fludrocortisone (.5mg/day ) can be useful in this condition

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Ventricular tachycardia is considered as one of the most  dangerous  cardiac arrhythmia .Rather , it is the label  VT  that spreads more  fear than the arrhythmia itself. It is a fact many patients with VT walk into hospital , still  VT will always be a sinister arrhythmia as long as it carries a risk of degenerating into ventricular fibrillation.

What determines hemodynamic stability in VT ?

  • Origin and location of VT
  • The ventricular rate
  • Presence or absence of AV dissociation
  • Impact on mitral inflow pattern
  • Associated left ventricular dysfunction or valvular heart disease.
  • VT in the setting of acute coronary syndrome.(Ischemic VT)
  • Inappropriate drug selection

Origin and location

VTs originating high up in the ventricle( High septal VT,Proximal VTs) have more organised ventricular contraction  and they are more stable.Distal VT  originating  in the myocardium away from the conducting system has chaotic myocyte to myocyte conduction.These are very unstable.

The term fascicular VT is nothing but VTs originating  in the His bundle and it’s branches( Can also be termed Septal VT ).These VTs are also stable and some of them respond well to calcium blockers indicating that they are very close to the AV junction and carry the properties of junctional tachycardia. QRS width gives  a rough estimate about the location of VT. Narrower the VT higher it’s origin.( But remember even in VT ,  qrs can further widen on it’s way downhill !)

LV dysfunction.

This is probably the most important determinant of the outcome in VT. Patients with severe LV dysfunction (EF <30%) fare badly .Hence the land mark concepts from MADIT 1& 2 demanded ICDs in these patients.The most common clinical setting is  dilated cardiomyopathy.SomE of them have bundle branch re entry(BBR).This particular  VT can be stable for many  hours.

Ventricular rate.

Usually VT has a rate between 120-200.Higher the rate of VT more the chances of instability .This rule is also not always true as fascicular VT can be well tolerated at high rates.So location of VT focus  and LV dysfunction usually over rides the impact  of ventricular rate.

Mitral inflow pattern

Proper left ventricular filling is the key to hemodynamic stability in VT. In proximal, septal,fascicular, LVOT VTs doppler studies  suggest (ACC /AHA Type C evidence : Personal observations in CCU during VT) near normal preservation of  bi modal filling of mitral valve inflow.In ischemic myocardial VT  the mitral inflow profile is critically affected . There is no distinctive forward filling was observed .In fact  at rapid rates a short pulsatile MR jets are noted instead.

Associated valvular diseases

It is obvious,  aortic  and mitral valve disorders can aggravate the hemodyanmic instability.

Final message

The clinical behavior of  ventricular tachycardia is widely variable and dependent on multiple factors.

Associated LV dysfunction and  structural heart disease ultimately determine the outcome.


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The pressure tracing between two chambers of the heart are distinctly different .

 Apart from the magnitude of the  pressure ,(LV at systemic pressure ) The morphology also changes.

  •  RV pressure curve is triangular in shape,
  •  Upstroke is not rapid , (Low dp/dt)
  •  There is no sustained peak ,
  •  There is an early fall and
  •  The pressure falls to zero which  never happens in LV.

Contary to this LV pressure curve is bullet shaped,  with a rapid upstroke, sustained peak, fall later, and does not touch zero.

RV/LV pressure curves in normal persons .Adapted from , Curtiss 1975 Circulation

Note : The shapes of RV curve will change in pathological states.Example in TOF, large VSD there will be left ventricularisation of RV pressure wave forms. Also  in pulmonary hypertension RV pressure may mimic a LV curve.

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