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Home : Patients : About Atrial Fibrilation

About Atrial Fibrillation

What is Atrial Fibrillation?

Atrial Fibrillation (AF) is a cardiac rhythm disorder caused by chaotic electrical impulses within the heart. It is a fast, irregular heartbeat originating in the atria. The heart is divided into four chambers, the upper two are the atria, and the lower two chambers are the ventricles.

The heart is an electromechanical pump. The pumping action of the heart relies on its electrical system to contract the muscles and pump blood throughout the body. The right side of the heart receives unoxygenated blood from the body and then delivers it to the lungs to be oxygenated. The left side of the heart receives oxygenated blood from the lungs and pumps it out to the rest of the body. The rhythmic contractions require electrical signals to reach each chamber in an organized, controlled manner.

The heart's electrical system is called the Cardiac Conduction System. It is made up of specialized cells within the heart muscle tissue. This conduction system carries electrical signals in a properly timed sequence to the muscle cells throughout the heart.

The normal electrical heart beat starts in the right atrium within a specialized group of cells called the Sino-Atrial (SA) node. The SA node is the heart's "natural pacemaker," regularly discharging an electrical signal that, under normal circumstances, is responsible for setting the heart rate. The normal heart rate is usually 60 to 100 beats per minute.

The signal generated in the SA node spreads throughout the atria until it reaches the Atrio-Ventricular (AV) node. After the atria contract and fill the ventricles with blood, the signal travels down the Bundle of His (pronounced "hiss").

The electrical signal is then distributed widely throughout both ventricles by the Purkinje Fibers. The ventricles contract at the same time. Since the ventricles pump blood to the lungs and the body, they are composed of a larger amount of muscle tissue than the atria. The left ventricle is the stronger of the two ventricles, generating higher pressure in order to pump oxygenated blood through the entire body. In the normal heart, the four chambers work in rhythm with each other to ensure that oxygenated blood is delivered throughout the body. The heart's conduction system must function properly to make the heart an effective pump.

When this conduction system is functioning properly, it is known as Normal Sinus Rhythm. When the electrical signals are fired in a chaotic uncontrolled manner AF can result.

The signs and symptoms of AF include:

Risks associated with AF:

Diagnostic Procedures

AF is routinely diagnosed using an electrocardiogram (EKG or ECG), in which electrodes are placed on the skin to record the electrical signals of the heart. However, sometimes electrocardiograms are unable to locate the origin, or focus, of the AF.

Sometimes a longer recording is needed. A Holter monitor records EKG signals while the patient continues normal daily activities. A Holter monitor usually records for 24 hours.

An exercise EKG test may also be done. This involves recording the EKG while the patient is exercising either on a bicycle or treadmill. The activity may bring on arrhythmias (irregular cardiac rhythms) that may not be recorded during a resting EKG.

These tests diagnose the arrhythmia. An electrophysiology (EP) study may be required to identify the origination or focus of the arrhythmia. The EP study involves placing catheters with electrodes inside the chambers of the heart. These electrodes record the electrical signals generated and map the location of the focus.