The heart's co-ordinated pumping action is controlled by a special electrical system. Elsewhere in the body, muscles are controlled by nerves. Brain thinks, nerve fires, muscle contracts. The heart's 'nerves', however, are within the muscle itself. These special muscle cells are living a double life as part of a conduction system. The undercover agents link together to form tracts, passing a message of contraction from one to another along the line - and from there, a Mexican wave of information spreads to the rest of the heart muscle resulting in a nice, timely contraction. 

As discussed in our general overview, the sinoatrial node is a cluster of these special cells working within their headquarters in the right atrium. It is the drummer of the band, deciding the tempo and keeping the beat. 

Unfortunately, often through bad feedback from damaged speakers (the heart itself in this metaphor), the rhythm becomes chaotic and the drummer loses control - resulting in an irregular rhythm. 

Atrial fibrillation is an extremely common irregular rhythm, mostly seen in older patients. It can cause symptoms such as a flutter in one's chest, light-headedness/fainting and even chest pain or shortness of breath. So, what's going on?

The job of the sinoatrial node is to set the pace and deliver that message to the AV node (a different headquarters of special cells) which resides in the septum (wall through the middle of the heart). From there, the message is sent along into the ventricles. While the message is being delivered from the sinoatrial node to the atrioventricular node, the atria contract in a nice, smooth manner to pass blood into the ventricles. By the time the ventricles get the message to contract, they will be full - ready to go. 

In atrial fibrillation, the message from the SA node to the AV node either doesn't happen, or the post is lost in the mail on transit. All of the other muscle cells start to contract independent of one another in a chaotic manner - hence, "fibrillating".

This causes two problems. Firstly, without a joined effort, the efficiency of delivering blood into the ventricles is compromised. And secondly, the AV node gets confused - receiving messages to contract from all over the place, rather than the single message from the SA node. It allows plenty of these inappropriate messages through the gate - and the ventricles are instructed to fire rapidly. 

Your heart rate will be far too high, often seen at 150 beats per minute even when relaxing in your favourite armchair. The fast heart rate leads to pump inefficiency. A lack of blood can reach the brain...hence the light-headedness or collapse. And, a lack of blood can reach the heart muscle itself...hence the chest pain. The fluttering sensation is driven by a very fast heart rate. 

So, your heart's conduction system is awry. What now? Well, it depends. 

If you have the paroxysmal type (the funny rhythm comes and goes) - we can try to correct it with medication or even a shock via pads at a low voltage. Sometimes these patient's atrial fibrillation is triggered by an infection - in which case we try to treat the underlying cause.

If you have the persistent type, with no clear underlying cause - we won't be able to make the rhythm regular again, but we can give medication to slow the rate and therefore improve the symptoms. 
Beta blockers (bisoprolol, metoprolol, atenolol, etc.) support the AV node with more troops, meaning less inappropriate messages get through the gate to the ventricles. We can titrate the medication until we find a nice range (60-100 beats per minute).

The other medication you will need is a blood thinner - usually apixaban or rivaroxaban. Why? Because the weird, wavy motion of the atria in this rhythm makes you more likely to form clots and have a stroke. We give the blood thinner to mitigate that risk.