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The conundrum called cardiomyopathy ! How is DCM different from RCM ,NDCM and MDCM ?

Posted Dec 12 2010 1:26pm

Dilated cardiomyopathy (DCM )  is the commonest  cardiac muscle disease .Diagnosis is simple and straight forward. All that we  require is,   documentation of LV dilatation and contractile dysfunction.The nomenclature of cardiomyopathy has remained a difficult exercise .This   is primarily  due to   iatrogenic  & intellectual confusion  among  cardiologists . They mixed up etiological and morphological entities together ,   later on  they  wanted to de-link  etiology from morphology  ,  ultimately they realised  when illness strikes the heart ,   it   can not differentiate the  morphology, etiology and pathology as we would want to   . So , whenever possible we have to label  cardiomyopathy with all components (Dilated cardiomyopathy due to alcohol with some restrictive features.)

This article  tries to evoke  some thoughts    about  why  LV dilatation  is central to the understanding of cardiomyopathy.

DCM is the prototype where LV dilates with global hypokinesia.The upper limit of   LV diameter is generally considered to be 56mm in diastole.  (Range 35 -56mm) .This cut off  point is too empirical  for the simple reason, the  left ventricle can dilate   up to  50 %  from it’s basal diameter and still technically  be within normal limits.( A 3.5 cm LV ( end diastolic diameter ) can dilate to 5.6 cm ,i e  a 50 % dilatation , still LV  has not reached the upper limit of normal  )

Even as we do not have a clear  answer to the above issue , we  recognise  left ventricle muscle can hypertrophy, progressively  dilate , transiently dilate, fail to  dilate ,  regressively  dilate  or  hypotrophy .These changes can be dynamic and heavily influenced by hemodynamic and local pathologic factors like fibrois, interstitial proliferation etc. Meanwhile , the pharmacological ,   surgical /catheter injuries we  inflict    , modifies  the muscle behavior in a positive or negative manner.

In this back ground ,  we have found a new entity called NDCM .

Apart from  DCM, a newer form of  cardiomyopathy  is being recognized  .This is often referred to as NDCM (Non dilated cardiomyopathy)  .Global  systolic LV dysfunction  with normal  LV dimension.This a similar to the terminology MDCM (Minimally/Mildly  dilated  cardiomyopathy  where LV dimension  do not  increase  beyond   15 %  upper limit of normal  ) .

This is seen in CKD and diabetic individuals.Atria may be enlarged .Diastolic dysfunction may co exist.  It is no surprise,  this entity closely mimics RCM. But in RCM LV systolic function  is not greatly compromised till the  late stages , while NDCM it begins with systolic dysfunction. This is the only difference .There can be overlaps .

MDCM was reported in 1990  . Keren gave a excellent insight about the condition  ,  It is unfortunate it failed to take off as a popular  clinical entity .  Cardiologists are argued to use this term liberally in their clinical practice .

Final message

Cardiology is not  that  simple as one would like to ! The two components of cardiomyopathy ie   LV dilatation and LV dysfunction can be temporally dissociated  one may precede the other. To  complicate the matter further, one of them may not manifest at all !

Few ,  still consider many of the RCMs and NDCM are one and the same entities that present in different time frames in their natural history.

So the simplified  concept  to decode the cardiomyopathy conundrum  could be

  • When both  dilatation and dysfunction occur it is classical DCM
  • When dysfunction  alone occur without dilatation it is NDCM
  • When both dysfunction  and dilatation are less it is RCM*(Relaxyl dysfunction must)
  • When dilatation is mild and dysfunction is severe it  is MDCM

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