Posts Tagged ‘lv function’

Assessing   LV function is the most common indication  for doing  echocardiography .Sinus tachycardia is the most common cardiac arrhythmia in humans. So, it is no surprise we encounter the above  situation  very often  in echo labs.

The principle behind echo assessment of LV function is to measure the  left ventricular wall thickening and the resultant reduction in LV cavity size.

The LV wall thickens in  systole and  returns  to baseline  thickness in diastole.When the heart rate increases the  rate of thickening has to be faster,  as do the rate of subsequent thinning in diastole. The endocardial segment of systole and thin segment of diastole tend to overlap at the base . borders are too shaggy and many times the thick So identifying true reference point  for endocardium become a difficult task.

It is  ironical  ,  inspite of  M mode echo  being termed outdated and obsolete by  most Echo schools , it remains the most utilized modality to measure LV function . It is  highly unlikely  , M-Mode derived LV EF   will be  replaced in the near future .This is because   “simplicity will always   prevail”  over  quality and accuracy .

It is all the more important  ,  the already poor index of M-Mode – LV EF %  becomes further  error prone at high heart rates.

It need to be emphasised , the impact of tachycardia in confounding  the true EF is greatest in  patients with preexisting LV dysfunction .

In a normal heart the errors are less and it can be  safely stated , tachycardias  rarely result in clinically important LV function errors

Does 2D derived EF by modified Simpson  overcome the problem of tachycardia related errors ?

To a certain extent ,  “yes ” . Here again the endocardial excursion is so fast one might have difficulty in marking the border.Automated  border detection algorithms are never corrected for heart rate related errors.

Other issues in LV function assessment  during tachycardia

In the presence of CAD  , the coronary arteries  often have varying degrees of obstruction.  Hence ,the  myocardial  segments  also exist  in varying degrees of ischemia.

In patients with significant CAD ,tachycardia due to any cause (Compensatory /Non compensatory -Fever, anxiety etc) can be considered a stress to myocardium . (By all means ,  can  we  consider it   an  equivalent of  dobutamine   stress echo! ?)

We know , dobutamine stress echo , has a variable effect on the contractility of LV. It can either  depress , argument, or  have neutral effect .Different lesions have different response depending upon the baseline viability of myocardium . For example  a 70% lesion  subtending a infarcted  –  viable segment may improve , while a 90% lesion supplying a normal LV segment may either worsen or hypercontractile .

What is poor man’s viabilty test ?

Grossly differing LV EF % in two different echocardiograms at two  different heart  rates may be an indirect clue  for the presence of viable myocardium.(Poor man’s PET or Thallium !)

The final message

The above concepts remind us the complexity of measuring the true EF in the presence of CAD. Purists,  may even question the existence of  a ” true normal  EF” in  a given patient

So, in the presence of marked tachycardia what is the ideal advice ?

  • Aviod measuring EF % during tachycardia , atleast in patients with CAD.
  • Use simpson method whenever possible
  • Atleast attempt it  few times,  you will overcome the laziness !

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