Atrial Fibrillation – an introduction

Lots of people come to see me with atrial fibrillation or AF as it’s often known.  While they might have been given a diagnosis, they often haven’t had time to discuss the implications and options for treatment.

The problem is that Atrial fibrillation is both incredibly simple and quite complex at the same time.

When I asked one of my junior doctors to do a presentation on it – he said that would only take half an hour, not realising that you could easily write an entire textbook on the condition!

So here is some useful information as a starter – there’ll be some follow up posts in the coming weeks.

The heart has 2 atria and 2 ventricles.  The atria collect blood from the body and pump it into the ventricles which then pump blood around the lungs and the body.

In atrial fibrillation the atria don’t pump properly – the electrical activity in the atrium is chaotic rather than regular and this means the tissue is writhing rather than a coordinated pumping.

This leads to two consequences.

Firstly, the atrioventricular node (shortened to AV node), the only normal electrical connection between the atria and the ventricles is bombarded by the chaotic electrical activity of the atrium at over 300 times per minute.

Fortunately it can’t work that fast, but it will be activated and trigger the ventricle irregularly at usually between 150-230 beats per minute.

This means the pulse is fast and irregular.  Not all the heart beats can be felt in the pulse at the wrist because the heart may not have enough time to fill properly and therefore the ventricles may not pump a lot of blood with every heart beat. Feeling the heart beat itself on the chest or the pulse in the neck is probably a better way of working out the heart rate.  But to clinch the diagnosis, an ECG (electrocardiogram) is needed.  This can even be done using smartphone or smart-watch accessories!

Secondly, because the atria are not contracting properly in a coordinated way, blood can stagnate within the atria and form clots, usually in part of the atrium called the appendage.  Not really a problem if the clots stay in the atrial appendage, but if a bit breaks off, it can cause a stroke.  This is one of the commonest causes of strokes and it actually tends to cause worse strokes than other causes.

So the initial treatment of atrial fibrillation focusses on controlling the ventricular rate and on assessing the risk of stroke.  That will be the subject of another post!


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