Atrial Fibrillation and Your Heart

Your heart has its own electrical system. The process by which electricity flows through your heart is called cardiac conduction. The cycle of electrical impulses signals your heart muscles to beat in a coordinated rhythm. This creates a pumping action that supplies your body with oxygenated blood.

When the cycle of cardiac conduction is disrupted, or the electrical impulses are irregular, cardiac arrhythmias are produced. Atrial fibrillation (AF) is the most common type of cardiac arrhythmia. An estimated 5.1 million Americans are now affected with this type of irregular heartbeat. ²

Cardiac Conduction

Cardiac conduction is the cycle of electrical impulses within the heart that cause the myocardium (muscle) of the four cardiac chambers to contract.

In a healthy heart, the conduction cycle begins with an electrical impulse across the Sinoatrial (SA) node, which is located atop the right atrium. The impulse travels across the right atrium to the left atrium, causing both atria to contract. The impulse continues down the atrium to the Atrioventricular (AV) node and down the Bundle of His located at the top of the ventricles. It then continues down the right and left crura, and finally through the Purkinje fibers causing the right and left ventricles to contract. As these impulses dissipate, the atria and ventricles relax.
heart in normal sinus rhythm heart with atrial fibrillation

During atrial fibrillation, some electrical impulses begin outside of the normal cardiac conduction system. These impulses cause rapid, disorganized contractions within the atrial muscle tissue. With multiple, uncoordinated contractions happening simultaneously within the atria, a single, whole-chamber contraction is not possible. Without the necessary whole-chamber contraction, the ventricles do not receive a sufficient amount of blood from the atria.

As these erratic electrical impulses continue down through the heart, they are either absorbed or blocked by the AV node. The ventricles may also contract with an irregular rhythm which further disrupts the coordination between the atria and the ventricles. If the aberrant electrical impulses are blocked by the AV node, the ventricles will tend to contract more slowly than the atria. This slower ventricle rhythm distinguishes atrial fibrillation from atrial tachycardia and atrial flutter.

2. Miyasaka Y, Barnes ME, et al. Secular trends in incidence of atrial fibrillation in Olmsted county, Minnesota, 1980 to 2000, and implications on the projections for future prevalence. Circulation. 2006;114:119-125.