What is Atrial Fibrillation (A.F.) Simplified

Atrial Fibrillation – With Sound FX

Atrial Fibrillation is the most common irregular heart rhythm that I encounter in my work. Over 1,000,000 people are known to be affected by AF thats around 1.5-2% of the general population. Whats more is that there are plenty of people that are walking around undiagnosed.

What is happening in Atrial Fibrillation.

In jargon it is described as “fibrillation in which the normal rhythmic contractions of the cardiac atria are replaced by rapid irregular twitchings of the muscular wall; the ventricles respond irregularly to the dysrhythmic bombardment from the atria.” Luckily I have never been one for gibberish.
Cardiac Pacemaker atrial Fibrillation
Sinus Rhythm
Let us remind ourselves of the normal conduction of the heart and especially the normal way the top half of the heart beats (the Atria). So the hearts natural pacemaker (red dot) normally fires around 60-80 times per minute (This corresponds to your hearts beats per minute). Once it has fired the cells around it have a knock on effect with one another and a natural contraction occurs across the atria (Green Arrows). The red line (Atrio-Ventricular Septum) is a barrier where this knock on effect is blocked from going any further and influencing the bottom of the heart (Ventricles). This is like a stone being dropped in the ocean, the stone would land at the red dot and the wave (green arrows) would move outwards in sequence until it reached the small blue dot.

This blue dot is a gateway called the AV Node, the A.V. Node receives the signal (as the wave hits it) it then issues a small delay before telling the bottom of the heart to contract. This happens 60 times in a minute with someone of a heart rate of 60bpm….
In A.F. the normal systematic and repetitive nature of the top of the heart is replaced by chaos. The exact trigger for AF is still up for debate, but risk factors are known to be heart failure, high blood pressure, diabetes, advanced age, hyperthyroidism and heart disease. It also doesn’t help if you have had a heavy night or excessively drink alcohol! (I know I know, sorry to break this news!)
Cardiac Pacemaker atrial Fibrillation
Atrial Fibrillation
I just want to define how chaotic the Atria are in AF. Imagine a house in the suburbs with a nice family that all got work or school each day and have a very socially acceptable routine. This is the Atrium during Sinus Rhythm. Now, that family goes on holiday and leaves their 18 year old son alone for the first time. He throws a party, advertises it on Facebook, 10,000 people turn up and one of his new found internet friends has bought with them copious amounts of alcohol. By midnight, this house party represents your Atria in Fibrillation – Chaotic.
In Sinus Rhythm the cells are dependent on the Sinus Node to tell them to contract. However in Atrial Fibrillation they become self sustaining. There is no order to the contraction of the cells the order that they fire in is totally random. No sooner as a cell contracted and relaxed than another stray wave has hit it and told it to do the same again.
If you could hear Sinus Rhythm in the Atria it would sound like this…
If you could hear Atrial Fibrillation in the Atria it would sound like this…
Now the bottom of the heart is still functioning normally but the AV Node is caught up in all this mayhem bombarded with IRREGULAR signals from the top half (sometimes up to 300 signals a minute). The AV node can’t keep up and it doesn’t really know what to do so it only passes on some of these signals,  How often the AV Node passes on these irregular signals is what affects how quickly or slowly your bottom part contracts. What is guaranteed is that it will be irregular.
The animation below shows Atrial Fibrillation and why it can cause Stroke.

Slow AF/ Fast AF

We pretend that we don’t use these terms… that’s a white lie (I definitely do) but essentially this is the rate of the lower part of the heart during AF. If you become bradycardic (Less than 50bpm) then we say this is slow AF. If you become Tachycardic (More than 100bpm) we would say that this is fast AF.

Stroke and AF.

Stroke is caused when a Thrombus (a bit like an internal scab causes when blood platelets group together) reaches a blood vessel in the brain and blocks it off so blood cannot reach the part of the brain that the blood vessel previously supplied. Atrial Fibrillation gives the opportunity for thrombus to form in the heart, these can potentially break free and end up in the brain.
To me blood platelets in blood plasma are like children at a water park. Imagine a group of children in some water rapids, when the water is moving quickly they are unable to join together to make a human raft because they are being buffeted by the powerful currents and waves. If the rapids suddenly slows then the children will all be able to grab on to one another and group together. AF causes a slowing in blood flow, the muscle doesn’t contract and push the blood down into the Ventricles, they fibrillate (a posh word for twitching). 

Why do I feel like (enter expletive here) when I am in AF?
Well actually it is thought that that half of patients don’t know they are in AF, these are the UNLUCKY ONES and I will tell you why, when AF lasts a long time you have a greater risk of having a stroke. If you feel like rubbish then it is likely you will be diagnosed and anticoagulated (medication to reduce your risk of stroke).

Those that do feel like rubbish there are two main reasons. Firstly your heart rate is normally inappropriate, either too fast or too slow this can mean either too much or too little blood is being supplied to the different parts of the body and this can make you feel pretty poorly. The other reason is that in AF you lose your Atrial Kick! This is a term that refers to the extra stroke volume (amount of blood pumped in one beat) that is gained when your Atria are functioning properly. It is thought that up to 30% of the stroke volume is down to the extra filling of the Ventricle that the Atria are responsible for. The Atria push extra blood into the Ventricle before they contract… in AF this doesn’t happen.
I hope this clears up AF a little,

Further Explanation is available here HASTE-Heart and Stroke Trust Endeavour

Right time for some Press Ups.

Thanks for Reading

Cardiac Technician

Comments 1

  1. A very simplified,descriptive and accurate account of A.F.Especially the sound effects for fast A.F as my heart feels exactly the same as this sounds.

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