What triggers the initiation of atrial fibrillation?

Focal tachycardias are significant contributors to the initiation of atrial fibrillation. In atrial fibrillation, the electrical activity in the atria becomes disorganized, leading to rapid and irregular heartbeats. Focal tachycardias arise from ectopic foci, often located in the pulmonary veins, which can fire rapidly and trigger the atrial fibrillation. The re-entry circuits established by these ectopic foci can disrupt the normal sinus rhythm and result in the chaotic electrical activity characteristic of atrial fibrillation.

In contrast, ventricular ectopy generally refers to irregularities originating in the ventricles, which may cause palpitations but are less likely to directly initiate atrial fibrillation. Heart failure can lead to atrial fibrillation, but it is more a result of structural and electrical changes in the heart rather than a direct trigger. Sinus bradycardia, characterized by a slower than normal heart rate, does not typically act as a trigger for atrial fibrillation, as it reflects a decreased rate of impulses from the SA node rather than a rapid ectopic firing.