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Atrial fibrillation is the most common type
of cardiac arrhythmia. In a healthy heart,

the sinoatrial node or SA node initiates all
electrical impulses in the atria. In atrial

fibrillation, electrical impulses are initiated
randomly from many other sites called ectopic

sites in and around the atria, commonly near
the roots of pulmonary veins. These un-synchronized,

chaotic electrical signals cause the atria
to quiver or fibrillate rather than contract.

Although the atrial rate during atrial fibrillation
can be extremely high, most of the electrical

impulses do not pass through the atrioventricular
– the AV - node to the ventricles. This

is due to refractory properties of the cells
of the AV node. Those that do come through are

irregular. Ventricular rate or heart rate
is therefore irregular and can range from

slow - less than 60 - to rapid -more than
100 - beats per minute.

On an ECG, atrial fibrillation is characterized
by absence of P-waves and irregular narrow

QRS complexes. Reminder: P-wave represents
electrical activity of the SA node that is

now obscured by activities of multiple ectopic
sites. The baseline may appear undulating

or totally flat depending on the number of
ectopic sites in the atria. In general, larger

number of ectopic sites results in flatter

As the atria do not function properly, the
heart puts out less blood, and heart failure

may occur. The most common complication of
atrial fibrillation, however, is the formation

of blood clots in the atria. As the atria
do not empty completely into the ventricles,

the blood may stagnate inside the atria and
blood clots may form. These clots may then

pass into the bloodstream, get stuck in small
arteries and block them. When a blood clot

blocks an artery in the brain, a stroke may



Atrial Fibrillation Anatomy, ECG and Stroke, Animation.

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alex 2017 年 10 月 14 日 に公開
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