Cardiology Teaching Package
A Beginners Guide to Normal Heart Function, Sinus Rhythm & Common Cardiac Arrhythmias
How Atrial Fibrillation Begins
The actual initiating factor can be something as simple as an impulse released from an atrial ectopic focus (premature atrial contraction/PAC, see below). AF is then sustained by a number of ectopic foci within the atria releasing stimuli in a disorganised fashion. This is why AF tends to be fast and irregular.
Ectopic focus. An ectopic focus of conduction in the heart is an area that begins to release electrical stimuli outside the normal conduction pathways. A stimulus released from an ectopic focus can disturb the normal conduction and , in some cases, take over the pacemaker role of the SA node.
