Biology Stack Exchange is a question and answer site for biology researchers, academics, and students. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am wondering exactly what a-fib is (causes and symptoms).

I would really appreciate having a sample of an EKG with it (because in my limited research, I have found it nearly impossible to find just a sample piece of an EKG that has a-fib on it) with your answer, so I can actually get an idea of what it looks like. With the sample EKG, I would love to have a normal one beside it so I can kind of analyze the differences between the two.

share|improve this question

closed as off-topic by Majid, Bez, anongoodnurse, WYSIWYG, Chris Jan 19 '15 at 6:39

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Homework questions are off-topic on Biology unless you have shown your attempt at an answer. For more information see our homework policy." – Community, Bez, anongoodnurse, WYSIWYG, Chris
If this question can be reworded to fit the rules in the help center, please edit the question.

2 pretty much has exactly what you are after. – jonsca May 18 '14 at 14:38
@jonsca How about linking one of the images here and make it an answer? – Chris May 18 '14 at 14:45
@Chris My point was more that this was answered quite well by the first hit on googling "atrial fibrillation ekg". Wikipedia's chart is actually better, but I don't want to just copy large quantities of information from there. – jonsca May 18 '14 at 14:53
I know this problem. But you can at least earn the reputation for that. Write a short answer, add a picture, reference to the Wikipage. I think this is perfectly fine. – Chris May 18 '14 at 14:59
@Chris I would not mind at all if you (or anyone else) wanted to take that opportunity. – jonsca May 20 '14 at 10:03
up vote 4 down vote accepted

A human heart can be viewed as 2 hearts, the left and the right heart, each consisting of an atrium and a ventricle. The atrium's function is to fill the ventricle with as much blood as it can and the ventricle then pump the blood away. Also there is a system of valves to control blood flow on each side. Basically this is how our heart works.

Now, to make this system work we need to have a coordinated movement of atrium and ventricle, that is, first atrium is filled, then it pumps blood into ventricle, valve closes and then ventricle compresses. The movement of heart muscle causes currents that can be measured (this is the ECG pronounced EKG). These currents are representative of the movements of atrium and ventricles are expressed respectively as p waves (for atria) and qrs (for ventricles).

It is the case that atria are not very important and sometimes they can stop working properly. They now longer have coherent movement and stop helping to pump blood into the ventricles, but they still move. This event is called atrial fibrillation.

From this explanation one can expect that no longer p waves will be identifiable in the ecg, but instead a random noise overlapping with "normal" qrs representing normal ventricular movement. The movement is actually not exactly normal, because the ventricular contraction due to atrial fibrillation now occurs at random times, that is qrs complexes occur with random spaces between them. The explanation for this is rather more complex: there are bundles of specialized cardiomyocites with different frequencies of depolarization. The fastest ones are on SAN and basically guide the whole heart rhythm through specialized bundles. When you have atrial fibrillation, the depolarization signals no longer come from these preferential bundles, but from any part of the atria at random. This causes the ventricles to initiate motion at irregularly spaced intervals. I've included a photo of a normal rhythm and a atrial fibrillation side by side, but I hope you can use this explanation to find better ones by yourself in the web.

Note: don't confuse atrial fibrillation with atrial flutter. Flutter is a faster paced regular (therefore organized) atrial movement. It will appear as a saw-tooth shaped wave with regularly spaced qrs complexes.


Hope this helps.

Causes of atrial fibrillation are numerous, bur mainly high blood pressure, vascular disease, heart and lung disease among others. It can be asymptomatic in most cases or presenting with the symptoms of its underlying cause.

Please refer to for a quick overview.

share|improve this answer
To add to your answer I think you mean P waves aren't visible in AF and also old age could be added as a cause in isolation - it's very very common in the elderly – Rory M May 21 '14 at 20:26
Yes, thanks you are correct, it was a typo. I've corrected it now. – user27221 Nov 9 '14 at 0:18
Good answer. I disagree only with this: It is the case that atria are not very important and sometimes they can stop working properly. Atrial kick contributes 15-35% to the volume of blood in the ventricle. This extra volume in turn increases cardiac output by a similar 15-35%. That can make the difference between living well and living with congestive heart failure. – anongoodnurse Nov 9 '14 at 2:17
The relationship between the HF and AF does exist, but is only partially understood (see, and although atrial systole contributes to the loss of cardiac output, it is only one of the many possible reasons for it. – user27221 Nov 12 '14 at 2:36

Remember that except for the concluding pathway through the A-V bundle, the atrial muscle mass is separated from the ventricular muscle mass by fibrous tissue. Therefore, ventricular fibrillation.

The mechanism of atrial fibrillation, except that the process occurs only in atrial muscle mass instead of the ventricular mass. A frequent cause of atrial fibrillation is atrial enlargement resulting from heart valve lesions that prevent the atria from emptying adequately into the ventricles, or from ventricular failure with excess damming of blood in the atria. the dilated atrial walls provide ideal conditions of along conductive pathway as well as slow conduction, both of which predispose to atrial fibrillation. For the same reasons that the ventricle will not pump blood during ventricle fibrillation. Neither do the atria pump blood in atrial fibrillation. therefore, the atria become useless as primer pumps for the ventricles. Even so, blood flow passively through the atria into the ventricles, and the efficiency of ventricular pumping is decreased only 20-30 percent. Therefore, in contrast to the lethality of ventricular fibrillation, a person can live for months or even years with atrial fibrillation, although at reduced efficiency of overall heart pumping.

numerous small depolarization waves spread in all directions through the atria during atrial fibrillation. Because the waves are weak and many of them are opposite polarity at any given time, they usually almost completely electrically neutralize one another. Therefore, in the electrocardiography, one can see either no P waves from the atria or only a fine, high-frequently, very low voltage wavy record. conversely, the QRS-T complexes are normal unless there is some pathology of the ventricles, but their timing is irregular.

enter image description here

enter image description here

share|improve this answer

Not the answer you're looking for? Browse other questions tagged or ask your own question.