Atrial Fibrillation

Please note that this article is not comprehensive and neither is it formal medical advice.

Normally, the electrical signals that cause the heart to beat flow through the heart in an orderly and regular way. This is known as sinus rhythm.

Unfortunately, the electrical signals may flow in an abnormal manner and this is known as arrhythmia. The most common arrhythmia is known as atrial fibrillation (AF) and this becomes more common as people get older. It is estimated that at least 7% of people over the age of 65 have AF.

AF is important because it is a common cause of stroke and on average, people with AF are 5 times more likely to have a stroke. Fortunately, there are effective treatments which can reduce this risk.

A picture of a water cistern to illustrate filling of the heart.

A Water Cistern

Modern water cisterns have a small button and a bigger button to adjust the volume of the flush.

The cistern only fills after a flush. This may take some time and therefore, there may be frustation if 2 flushes are required in quick succession.

An image to show how a water cistern could be improved to improve filling.

A Super Water Cistern

It can be imagined that if another cistern were connected to and above the first cistern, then this might eliminate frustrating waits.

An image to show the arrangement between the left atrium and the left heart.

The Atria of the Heart

The main pumps of the heart are known as the ventricles. The right ventricle (RV) pumps blood to the lungs and the left ventricle (LV) pumps blood to the rest of the body.

The left and right atrium are connected to and above the ventricles. Both atria fill continuously. The left atrium fills with blood from the lungs and after each LV beat, the mitral valve opens and the LV fills quickly. Most of this filling is passive but towards the end, the left atrium also contracts and this contributes to 30% of LV filling.

An image of a wobbling jelly to demonstrate atrial fibrillation.

Atrial Fibrillation

The arrangement of the atria and ventricles provide for fast efficient filling of the ventricles between each heart beat. In sinus rhythm, the alternate contraction of the atria and ventricles are well co-ordinated.

In atrial fibrillation, electricity flows randomly through the atria. The atria do not contract. They tremor at a high rate. The ventricles do contract but in a completely irregular ("irregularly irregular") manner and usually, at too high a speed.

An image of a tapping hand to demonstrate the irregular irregular palpitations of atrial fibrillation.

Symptoms of AF

Patients with AF may experience palpitations which is an awareness of the heart beat. Doctors may ask patients to "tap out" their palpitations and AF is suspected if the rhythm is completely irregular.

As the atria do not contract, 30% of the LV filling is lost and this results in an equivalent drop in cardiac output. As a result, patients may experience breathlessness, dizziness, tiredness and even chest pain and blackouts.

An image of a snowman and snowflakes to demonstrate the smooth blood flow of sinus rhythm.

Smooth (Laminar) flow

In sinus rhythm, blood flow through the atria is smooth and this is known as laminar flow.

An image of a snowman and swirling snowflakes to demonstrate the turbulent flow of atrial fibrillation.

Turbulent flow

In atrial fibrillation, the atria are tremoring with swirling of the blood and flow is turbulent.

An image from a transoesophageal echo to demonstrate a blood clot in the left atrium with atrial fibrillation.

Stroke and anticoagulation

The turbulent flow can be seen when a transoesophageal echocardiogram is done. It looks like "smoke".

In AF, the atria are like "still ponds" and blood clots can form inside them. If these break off and reach the brain, they can cause a stroke. In fact, they can cut off the blood supply to any organ depending on where they end up. Anticoagulants are used to thin the blood and to reduce the risk of clots forming. In the past, warfarin was the only anticoagulant available but newer drugs known as Direct Oral Anticoagulants (DOACs) are now used.

An image of moonwalking to demonstrate heart rate and rhythm in atrial fibrillation.

Rate and Rhythm control

The only treatment that reduces the risk of stroke is anticoagulation. The other treatments for atrial fibrillation are for symptom relief.

Drugs such as flecainide and amiodarone and procedures such as DC cardioversion and pulmonary vein isolation are used to return the heart to normal sinus rhythm (rhythm control). Unfortunately, success rates are variable especially in the long term.

Drugs such as beta blockers, diltiazem and digoxin are used to control heart rate.

In summary, atrial fibrillation is the most common arrhythmia seen. When it occurs, risk factors should be addressed. These include excessive alcohol and caffeine intake, high blood pressure, stress and overactive thyroid activity. Atrial fibrillation is important because of the increased risk for stroke. The risk for stroke is dependant on a number of factors and can be estimated by the CHADSVASC score. Anticoagulation is recommended for those at risk.