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Posts Tagged ‘phases of diastole’

The mechanical atrial function   during atrial fibrillation remain a mystery . In fact , the general  belief  is during  AF  the mechanical function of atria is zero. This is why AF  is promotes stasis and   LA clot formation. It may appear theoretically correct  , still   AF especially coarse  still imparts some amount of  mechanical motion .But this usually does not translate to any useful hemodynamic function .

If atrial booster pump is lost (which is said to be 25 % of  LV filling )  suddenly one expects dramatic symptoms  especially if there is associated LV dysfunction or aortic valve disease .

But in real world AF is well tolerated arrhythmia in most  .  We know by land  mark trials AF  is as good as sinus rhythm  if the rate is  is under control

This is a definite evidence the AF  may not compromise  LV filling   even if   it nullifies  the  atrial contractility .

There is one  more evidence for  retention of atrial mechanical activity in spite of AF .It is well recognised , pre-systolic accentuation is preserved  in many cases of mitral stenosis with AF.

*Crazy hemodynamics : For an attached LA clot to  dislodge ,   one needs some amount of LA contraction isn’t ?  Unfortunately  a fibrillating  atria always  tend to  have this one ! This again is a senseless  proof for some  mechanical activity of LA during AF !

How is this possible ?

Is it a  purely volume dependent filling   ? ( Or )  is it  the  Intrinsic LA starling forces that do not depend electrical atrial activation .

This is definitely an  issue to ponder over . A good LV contraction makes the atria empty more completely . This would  somehow  mean , LV relaxation  is facilitating atrial function . During  AF the LV  handles effectively  the additional burden  imposed by the loss of   25  %  booster pump of atria ( Accelerated LV relaxation ? )  A  constantly  changing  RR interval makes LV diastolic function a more complex event .

Final message

Atrial fibrillation is  a well tolerated  arrhythmia in vast  majority of patients  . This  implies either of the two things.

  1. The so called  physiological atrial  booster pump is redundant  or dispensable in otherwise healthy heart
  2. The booster pump is indeed important  . . . but it is less  affected by AF as long as the rate is under control !

It is to be  strongly emphasized , Heart rate and  LV function  will ultimately determine  , how one is going to tolerate the AF  !

It is  a small gesture  from LV  to LA  at it’s hour of crisis  . . . in return  for  it’s lifetime assistance  as a booster pump ! 

Postamble

How  rate control  prevails over rhythm control in spite  zero atrial contractility in the  former  ?

Comments welcome !

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