Health knowledge made personal
Join this community!
› Share page:
Go
Search posts:

Acute myocardial infarction of LVOT : An unrecognised cause for refractory hypotension

Posted Feb 06 2010 1:23am

Hypotension is one of the dreaded complication of acute STEMI.

  • It can be due to either a  mechanical complication or hypovolemia.
  • The hypotension in inferoposterior MI is  often related to enhanced vagal tone and easily correctable with atropine  and fluid  administration.
  • RVMI is the classical example of hypotension that may improve with fluid resuscitation
  • Hypotension,  if  not reversible within 12  hours  ,  is more likely to  represent a more sinister mechanism like pump failureMR or ventricular  septal tear etc .

A new mechanism for persistent  hypotension is increasingly recognised.

This is due to the

1.Loss of LVOT dynamic activity.

2.Excessive  dynamism of LVOT.

LVOT contractile and ejectile falure

Even though LV  outflow tract  contain  less  contractile myocytes  it has an important mechanical  job to do. We know it’s  primary job is that of a  conduit  but  it also  has to  eject the blood into aorta with sufficient force.  In factit is thought much of the acceleration of blood velocity occur in LVOT . SoLVOT  plays a key role in maintaining the cardiac index.  An excessively dynamic LVOT will impede the forward blood flow as in HCOM.  Similarly  less dynamic contraction  of LVOT  results in  low velocity propulsion that interferes with   proper delivery of blood from LV cavity into the aorta .

These factors get amplified in  acute MI as it is a compromised situation with fluctuating HR and contractility. So a properly functioning  LVOT conduit is  absolutely mandatory.

STEMI due to a proximal LAD obstruction   located can involve the septal .If the first septal branch  happens to be a major one,  there will be  definite impact on the LVOT function.

Excessive dynamism  LVOT   desynchrony  LVOT collapse .

LVOT has a medial border formed  by IVS an  anterior surface and  a posterior surface .The lateral border is relatively boundary less except it is guarded by  the anterior mitral leaflet.

But one should recall the AML comes towards the LVOT only in diastole . When it comes in systole it becomes a pathological event  called  SAM  (Systolic anterior motion )

The LVOT wall desynchrony can occur in both anterior and posterior MI.In a mulivessel CAD  this can happen when there is disproportionate inferior to anterior wall motion defect.

Management.

  • There is no specific management strategies aimed at restoring LVOT function.
  • Emergency revascularisation will attenuate the mechanical dysfunction
  • Dosage of powerful inotropic agents should be moderated in dynamic LVOT obstruction.
  • Spontaneous recovery  may occur in few

Post a comment
Write a comment: