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In dilated cardiomyopathy which chamber dilates first ?

Posted Feb 09 2010 8:44am 1 Comment

As the name suggests   dilated cardiomyopathy  would imply  cardiac chambers will dilate at least some time in the course of the disease .It can be minimalmild or massive. A new entity called  non dilated cardiomyopathy is also gaining wider acceptance . (That will be dealt seperately )

Logic would suggest the first chamber to dilate in DCM  should be the left ventricle because it is  facing the direct load of systemic blood. But we also know whenever  LV is stressed left atrium comes to it’s assistance .

Left atrium does this    by total self sacrifice ( by all  means!)  increases  it’s  force of contractionelevating it’s  mean pressure or even increasing it’s rate (AF) .

Like most  other critical questions in cardiology  ,  the factors that determine LV dilatation in DCM ,  is  also poorly understood !

  1. Is it the after load ?
  2. Is it the  muscle mass ? or it’s turgid  or flabbiness ?
  3. Is it the interstitial integrity?
  4. Is it the blood volume ?(LVEDV ,  LV residual volume )

When the issue is complex it is  usual  to  make the   the unknown  genetic defects  ,  the scapegoat !

As of now the most important determinant of LV dilatation  could be  the behavior of the desminsthe gap junctions and myosins the titins etc

If  the LV of a DCM patient  refuses  or  resists  dilatation what  might happen ? Is it good or bad for the patient ?

Here is a catch .  A  LV  that does not dilate  obviously should be  be good for the patient  is in’t ? Medicine is not that simple.

When   LV  fails to  dilate  it means it has become  too  stiff and rigid    and pass on the  burden to  to LA which  faces the music. And in the process it dilates.This is the reason we  observe  diastolic dysfunction in vast number of DCM patients.( Currently it is estimated > 75% DCM will have significant diastolic dysfunction )

So now we can imagine how complex the sequence of hemodynamic stress in DCM that determine the chamber enlargement.( RARV  dimension in DCM is a separate issue !)

So now answer this question :  Which chamber dilates first in DCM ?

  1. Left ventricle
  2. Left Atrium
  3. Any of the above
  4. Both of the above dilate simultaneously

The answer must be 3 .

Why  recognising this sequence of  chamber enlargement  in DCM   is important ?

  • It gives us an opportunity to assess the dominant mechanism of LV dysfunction.There are reports where some  DCMs  have more diastolic dysfunction than systolic dysfunction  .This will have important therapeutic implication.Further many of the infiltrative   disorders of LV can have features of both DCM & RCM .
  • When a RCM begins to dilate it is usually  a harbinger of terminal heart failure. But,  it need not be always true .  A small restrictive LV  when  dilates   may acquire a  slightly improved diastolic properties as the  LV becomes more placid . And ,  if it happens the LA size may regress.
  • The role of LV restriction devices likeAcron meshDor procedureplication  in refractory  DCM is not well defined. All these   modalities actually  adds  a small dose of diastolic dysfunction in these patients who have grossly dilated ventricles. This fact is  very important  as presence of any preexisting  significant diastolic dysfunction in DCM makes  the role of LV restrictive devices and surgery a big question mark !
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