Deconstructed Cardiology

Atrial Fibrillation

01.10.2019 - By Gaurang_MDPlay

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Atrial fibrillation is an electrical abnormality in the heart. It affects the way the electrical wiring in the heart works.

Normally, the electrical impulse for a heart-beat begins in the right upper chamber, at a specialized site called the sinus node. This is a very organized system of electrical wiring explained in the basic anatomy section. If everything goes as per the plan, we have an organized rhythm, like a metronome or a pendulum. The rate of the oscillation may vary but the rhythm remains regular, to and fro (figure 1). 

Figure 1: Deconstructed electrical wiring of the heart.

In atrial fibrillation, instead of one single area initiating the impulse in an organized fashion, we have disorganized activity in the upper chambers. Imagine an Olympic sized boat with 40 rowers, listening to a single person in front who is setting the rhythm by shouting ‘Row!’. This is the normal heart. Now imagine various rowers standing up, in no particular order, and shouting ‘Row!’. Other rowers who are not standing up respond to the command, but this results in chaos. The rowers still sticking to their roles of rowing are completely disorganized and also have to paddle more frequently because of the constant commands to do so. This is atrial fibrillation (figure 2). 

Figure 2: Atrial fibrillation

This chaos is happening in both the upper chambers. The electrical impulses may fire as fast as >400 times a minute. If the lower chambers, which have the essential role to pump the blood outside the heart, start going at those rates then this can be fatal. Thankfully, the junction point between the upper and lower chambers (AV node, point#2 in figure 2) functions to filter out excessive impulses. This is because the junction node can only conduct the impulse so many times a minute. It is like the border crossing, irrespective of the number of cars lined up, only so many cars can be processed in a given time and can enter the other country.  

Symptoms: 

Nevertheless, the lower chambers speed up and may go at a rate of 150-200/minute or more at times. This can be enough to give some people symptoms such as palpitations, shortness of breath, chest pain, dizziness etc. On the other hand, some people may be completely asymptomatic and have no clue they are in atrial fibrillation. The manifestation of the symptoms depends on the effect the fast heart rate has on the body, while some people are excessively sensitive to heart rate change. 

While

the atrial fibrillation may be permanent, it could also be transient. A

big proportion of patients may flip back and forth from normal to

atrial fibrillation. This can cause occasional (and unexplained)

palpitations, dizziness etc. 

People

with otherwise normal heart do not miss the lack of contraction of the

upper chambers. It is the lower chambers which do the important job of

generating enough force to push the blood out of the heart to the body.

It is said that the upper chambers may contribute up to 10% to this

blood pumping function. Most people have enough reserve to not notice

the absence of this 10%. However, patients with poor heart function do

not have the luxury of an extra 10% to spare and these patients may

especially feel worsening of their symptoms when they go into atrial

fibrillation. 

Detection: 

The only good way to detect atrial fibrillation is to catch it in action. This could be through an ECG, telemetry, holter, event monitor or any other device tracking electrical acti...

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