AFib stroke prevention

Atrial fibrillation is one of the causes of stroke. When the atriums fibrillate they don’t contract and pump effectively. This means that the flow of blood through the atriums slows down. When blood slows down or becomes static it has a tendency to clot. If a blood clot forms inside the atriums it may subsequently dislodge, break away and be pumped out of the heart, a process called embolisation. As a large proportion of blood flow goes to the brain, this is the most common area for the blood clot to end up. A blood clot that is pumped into the brain will block the blood flow to the part that the blood vessel serves, causing injury. In its mildest form this may not be noticeable. There may be neurological symptoms, such as a loss of vision or speech, muscle weakness etc which recover completely in 24 hours. This is called a transient ischaemic attack (TIA). In the most severe form, permanent damage or death can occur. This particular type of stroke is called thromboembolic, meaning it is due to a blood clot that travels from the heart to block a blood vessel in the brain. Strokes that result from atrial fibrillation tend to be bigger and more dangerous than strokes from other causes.

The left atrial appendage, which looks like a pouch or sock that sticks out from the left atrium, is the area where clots form and embolise from in >90% of atrial fibrillation patients who suffer a thromboembolic stroke. As it is on the left side of the heart, any clot that is pumped out will go to the brain or other parts of the body, rather than the lungs.

The risk of a stroke is believed to be the same whether someone has paroxysmal, persistent or permanent atrial fibrillation. Anyone whose episodes last longer than 5 minutes has an increased risk. It is less certain what risk very short attacks, lasting less than 5 minutes, provide. It is safest to assume that documented short episodes may be a sign that at other times there are longer episodes, or that longer episodes may develop in the near future.

The stroke risk is the same whether someone has symptoms from atrial fibrillation or is asymptomatic and it is discovered by chance. Unfortunately, the development of a stroke or TIA is often the event that leads to the discovery of asymptomatic atrial fibrillation. This fact is important when considering the role of drugs, cardioversions and ablation to treat atrial fibrillation symptoms. If the treatment is successful and symptoms are abolished it doesn’t mean that the stroke risk has gone – it may just be that the atrial fibrillation is silent and the symptoms are masked. Even if monitoring shows a normal rhythm it is very difficult to guarantee that atrial fibrillation won’t return.

Atrial flutter carries the same risk of stroke as atrial fibrillation.

Even young, healthy adults with no heart rhythm problems have a risk of stroke; it is just that the risk is extremely low. Although atrial fibrillation can increase an individual’s risk of stroke by up to 5 times compared to an identical individual who doesn’t have the arrhythmia, the overall yearly risk of a stroke is heavily influenced by many other factors. If a fit and healthy man under the age of 60 develops atrial fibrillation, multiplying his baseline risk by a factor of 5 still produces a very low risk of stroke (estimated to be 1.3% or 1 in 77 over a 15 year period, equating to less than 1 in 100 per year).

CHA2DS2-Vasc score

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