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Conveniently forgotten studies in CRT : The importance of diastolic wall motion defect in cardiac failure !

Posted Sep 08 2009 10:24pm

The   failing heart  enlarges progressively and  attain a globular shape . What  looks  for the  naked eye  as a simple global hypokinesia of LV  , when  analysed  ,  reveal multiple  forms regional desynchronisation .This is especially true if the QRS complex is wide.

It is generally divided into three groups

  • Intraventricular desynchrony (IV)
  • Ventriculo-Ventriculo desynchrony(VV)
  • Atrio ventriculo  desynchrony(AV)

In our search for improving CHF mortality and morbidity  ,  we have  stumbled upon this concept of restoring the lost synchrony of the heart. Cardiac resynchronisation therapy  has become ( Rather projected to become !)  a  great modality for patients  with cardiac failure.It was   initially advocated only   for severe forms of cardiac failure  , now  advised even for class 1 CHF. (CRT-MADIT 2009)

Restoring  the lost  synchrony  by rewiring the cardiac conducting system with multiple leads and optimally timed pacing increases the effectiveness of cardiac contractility.It can improve EF, and also regress mitral regurgitation.

The above concept was perfect on paper , but was very difficult to replicate on real patients. CRT was ineffective in 30% of patients.   Many had partial  effect. Few had adverse effect .

The reason for the poor efficacy  is  technical in many .  Identifying the optimal  sites for  positioning  the leads  and the futility of such an  exercise as the LV epicardial  lead is pre- selected by the patients coronary venous anatomy are the major issues.An electrically ideal site for pacing  can  contain a  mechanically dysfunctional scar.   While these  technical issues may  be addressed  in due course  what worries us is the conceptual flaws.

Emerging  facts indicate timing of asynchrony could be vitally important.

  • Systolic   synchrony
  • Diastolic synchrony

What is the incidence desynchrony with reference to the cardiac cycle ?

CRT resynchronisation

One major reason that was overlooked totally was the presumption cardiac dysynchrony occur only during systole. It is a less recognised fact is the ventricular relaxation is not uniform and synchronous.A  failing ventricle can not be expected to relax  systematically and coherently  for the simple reason the myocytic calcium reuptake into the sarcoplasmic reticulum  is grossly impaired. This  is directly responsible for the diastolic dysfunction observed in dilated cardiomyopathy . If this impairment occur uniformly throughout the  left ventricle it can be termed global diastolic dysfunction which is little easier to correct .But what really happens is  the  defect in calcium reuptake occurs in a random fashion with lot of regional variation. This is called regional diastolic wall motion defect or regional diastolic dysfunction.The above mechanisms result in the typical restrictive filling pattern of many of the advanced  patients with DCM . CRT as a concept should need to address this issue.

How to diagnose Diastolic WMD?

The  fact  is  ,we have not  mastered the quantification of systolic WMD as yet. It may take years before decoding the  nuances  of diastolic wall motion defects. At least we need to know such a thing exists.Tissue  doppler strain rates ,  velocity vector imaging could be useful tools. As such they are not clinical tools.

Final message

crt cardiac resynchronisation asynchrony echocardiography

Cardiac resynchronisation as a concept is good on paper . Heart need to be synchronous both during systole and diastole .This becomes especially important in an advanced stages of  heart failure. Without proper follow up  and potential adverse effects of CRT on diastolic WMD ,   CRT concept    has  miles to travel !  . Some  pessimistic thinking   cardiologists ( Me . . . !)   would even argue  it as a case of prematurely released device into the  patient domain. Of course there is  lot of  scientifc data that  will vouch for its beneficial effects .(The latest being from the prestigious NEJM ,  CRT-MADIT) but it has to prove it’s worth in individual patients. Physicians must exercise caution  before embarking on heroic  attempts to provide resynchrony of failing hearts .

Reference

This study from France published in JACC 2005  byIris Schuster,

http://www.journals.elsevierhealth.com/periodicals/jac/article/PIIS0735109705021

Coming soon

ICDs are better bet than CRT

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