Pathophysiology of AF

Definition

•Rapid unorganized and ineffective contractions of the heart due to the rapid Atrial contractions.

Physiology

•Blood fills the atrium

•A contraction is generated by the atrium to pump the blood to the ventricle.

•A contraction is generated after that to pump the blood either to the rest of the body or to the lungs

•The cycle keeps on repeating

•A contraction is a result of impulses.

•The electrical impulses are generated by specialized cells in the heart. These cells are localized in particular area and are in charge of generating, transmitting and organizing the contractions.

•SA node à AV node > bundle of His > Purkinje fibers

•SA node is the leader of all those

•It is in charge of initiating all impulses.

•The impulses are transmitted to the AV node to insure organization.

•And then through the bundle of His and Purkinje fibers then to the rest of the ventricles

•As the contractions of the heart are crucial for survival, there are secondary pulse generating cells distributed in the atria so in case the SA node failed to work they take its place and generated impulses.

•These specialized cells are referred to as ectopic foci.

Pathophysiology

•In Atrial Fibrilation, what happens is that some ectopic foci work to generate impulse without co-ordination with the SA node.

•This unorganization results in rapid contraction of the atria.

•Out of those many impulses, only some get picked by AV node and transferred to the ventricles leading them to contract.

•E.g.So lets say 120 atrial contractions per minute will result in only 90 ventricular contractions

•Also the SA node works in a way to ensure the filling of the atrium before getting it to contract.

•When it fills, a contraction occurs to pump the blood and fill the ventricle.

•In case of unorganized rapid contractions, the atrium will pump before it fills. So the amount of blood received by the ventricles and therefore pumped will be insufficient.

•Distal parts from the heart will not get the needed amount of blood and this explains the symptoms.

Types of AF

•Paroxysmal AF

•Persistent AF;

•And permanent AF.