Atrial Contractions

Cooler asked:


If so, show me a detail medical reason for this phenonmenon. Why doesn’t the Atria have a valve to prevent back flow if the atria do contract. Where does the blood go? What is the mechanism of atrial contraction ?> Please give a most detailed as answer as possible. I need to proove this to a fellow classmate who refuses to believe the atria contract, he says its not possible because if the atria contract blood will flow back as there is no valve that sepeates the atra from the vena cavas.

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Ben Escomm asked:


In this article we are focusing on the heart itself and what is actually taking place in the chambers during afib. But first lets go to a normal heart for a second.

In a normal heart we have a “lub-dubb” sequence. If you’re not familiar with what I’m talking about, you can find a full explanation on my website but here’s a quick description so you get the idea:

The top part of your heart (atria) squeezes and makes a “lub” sound, then the bottom part of your heart (ventricles) squeezes to give the “dubb” sound. “Lub-dubb” is the sequence that comes from one beat of the heart.

Now that’s outta the way, on to the rest of the article:

The lub is created by a electrical pulse in the right atrium (right upper chamber). See, the heart has its own natural pacemaker called the SA node-its basically a part of that chamber which automatically fires an electrical pulse that causes the heart to contract or squeeze-first in the atria (lub) and then in the ventricles (dub). The SA node controls the rate at which the heart beats in a normal heart.

In a heart with atrial fibrillation the electrical pulse that is fired from the SA Node isn’t the only pulse fired. There are other sites in the right atrium called foci (plural for focus) that are firing pulses as well. These other sites are firing faster and at the same time as your natural pacemaker causing multiple contractions of your upper chambers, which is why, during afib, the atria looks like jello quivering (lublublublllubuubllublub) as opposed to a single unit making a single squeeze (lub).

Its these multiple pulses from the right atrium which cause the ventricles (and therefore your heart rate) to be irregular…and, as you recall it’s the AV node which helps slow the rate of contraction from the atria to the ventricles.

Need more explanation of the concepts I presented in this article? Click here to get a better idea with additional descriptions, pictures, and animation.

www.understandingatrialfibrillation.moogo.com



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