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.
- The so called physiological atrial booster pump is redundant or dispensable in otherwise healthy heart
- 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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Dr.S.Venkatesan MD 