We all know that the heart
beats continuously at a regular rate and rhythm. The upper chambers of the
heart are called the atria (single, atrium) and the lower chambers called the
ventricles. The impulse for the heart beat starts in a group of cells called
the SA node located in the right atrium. This causes the atria to contract and
empty the blood into the ventricles. The impulse also reaches another point
called the AV node that is located between the atria and the ventricles. The
impulses from AV node are carried through the ventricles allowing them to empty
In atrial fibrillation, the impulses start at a point outside the SA
node. This causes irregular contractions of the atria. There is loss of
coordination between the contraction of the atria and the ventricles, resulting
in variable and irregular amount of blood leaving the ventricles.
The pumping activity of the
atria is thus disturbed in atrial fibrillation, resulting in pooling of blood
in the atria. This stagnation of blood can result in the formation of blood
clots. The blood clots may travel to the brain resulting in stroke.
Atrial fibrillation can
cause symptoms of chest pain and sometimes heart failure. However, in some
patients, it may not cause any symptoms at all. This subclinical atrial
fibrillation can be detected with the help of pacemakers or defibrillators.
A recent study was conducted
on 2580 patients of 65 years or older, suffering from hypertension but no
obvious atrial fibrillation, with an implanted pacemaker or defibrillator. These
patients were followed up for a mean duration of 2.5 years.
The study found that
patients who suffered from subclinical atrial arrhythmias were at an increased
risk of nearly two and a half times of suffering from stroke or embolism
(presence of a clot in the blood) during the follow-up period.
atrial fibrillation that does not cause symptoms should not be ignored. Further
studies are required to see if treatment with blood thinners will help to
prevent stroke in these patients.
1 Subclinical Atrial
Fibrillation and the Risk of Stroke; Jeff S. Healey et al. N Engl J Med 2012;