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What is the difference between “Electrical wall motion defect” and “Mechanical wall motion defect” follo

Posted May 30 2010 10:14am

Regional wall motion defect( WMD) is the hall-mark of myocardial infarction.It can vary between complete akinseia to mild hypokinesia.

The wall motion defect is a gross terminology which is used  to describe any abnormal motion of the ventricular   segments.Technically,  hypo,   hyper , dyskinetic , akinetic  ,  even any vigorous  movement of LV segments will also come under the general category of  wall motion  defects. For example in extensive  anterior MI   the posterior segments show vigorous  contraction.Though . this compensatory motion  benefits many , it has a potential to adversely stretch the  scarred myocardium and promote aneurysm formation

What causes the regional wall motion defect ?

  • Infarcted segment
  • Ischemic segment
  • Adjacent normal segment behavior (Piggy pack effect, )
  • Loading conditions
  • Heart rate

Finally ,  and  most  importantly the timing and arrival electrical signal to these ill-fated segments determine the sequential activation fronts. Wall motion defect is a more complex phenomenon than we would tend to believe.

What are the  the classical examples of electrical wall motion defect ?

  • LBBB
  • Pre excitation
  • Some forms of VPD

*LBBB causes a paradoxical septal motion with  reference to lateral fee wall contraction.It is still a mystery ,  this paradoxical motion does not cause any  mechanical  disadvantage in structurally normal hearts  .

WMD  in combination  of  LBBB  and  STEMI

We know ,   LBBB   due to ischemia or infarct carry a  sinister prognosis .

Here , there  is  ”Double wall motion defect”  . One electrical and two ischemic .  We do not know , how LBBB influences the ischemia/Infarct related wall motion defect and vice versa. .  This is the reason ,  there is a large chunk of  poor or non responders  for cardiac resynchronisation therapy.

Can peri infarction  blocks and other non specific   intra  ventricular  conduction defects alter the sequence of  ventricular  contraction ?

We do not know .It is distinctly possible.Tissue doppler studeis have indicated this.

What is the influence  of  heart rate on the  of Wall  motion defect ?

An  otherwise insignificant regional wall motion defect  could be  amplified with tachycardia . Paradoxically , (as in a biphasic response to dobutamine stress test )  a significant WMD may be attenuated at a particular heart rate.  So, the influence of  HR on  WMD is  as simple as  it could be  ! ! !

Which  is the best time to assess  LV  function  after  MI ?

Considering these issues , LV function  assessed  at discharge ,  may not give us the exact quantum of  muscle damage.  4 weeks may a  reasonable  time frame . This is important in the current era  as presence of  significant  LV dysfunction  becomes an indication for revascularisation  .We  can’t be offered,  to err on this vital LV functional parameter.

Final message

WMD  is a combination of  electrical, mechanical , structural,  alteration in response to variety of myocardial insults.It is very hard to assess  individual components contributing to the net WMA. The easiest and surest way to  quantify  WMD  due to  muscle damage is to  do a deferred echocardiography , when all time related WMD ( Ischemic  stunning , perinfacion block )  disappear.

Coming soon

Diastolic wall motion defects .Is wall motion defects exclusive phenomenon of  ventricular systole ?

No , definitely not. Regional relaxation abnormalities are quiet common .it is poorly recognised .

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