What is an Arrhythmia?

An arrhythmia refers to an abnormal rhythm of the heartbeat. Arrhythmias can happen if the heart beats too fast, too slow, or beats with an irregular rhythm, as is the case with atrial fibrillation, the most common arrhythmia in the United States.

Most arrhythmias are harmless, but some can be serious or even life threatening. When the heartbeat is too fast, too slow, or irregular, the heart may not be able to pump enough blood to the body. Lack of blood flow can damage the brain, heart, and other organs.

Everyone has felt their heart "skip" a beat or two and speed up in times of fear or excitement or during exercise. Too much caffeine and certain medications also can cause heart palpitations in some people. These types of arrhythmias are generally harmless.

However, if irregular heartbeats are frequent or chronic, they can be serious — and sometimes life threatening. The consequences of having an arrhythmia usually depend not only on symptoms they can cause (such as faintness) but also on the presence of important abnormal structural conditions of the heart and/or heart disease.

Human HeartThe Heart’s Natural Electrical System

The normal rhythm of the heart is a tightly regulated but dynamic phenomenon that changes according to the metabolic needs of the body. The heart has built-in pacemakers and "wiring" that coordinate contractions in the organ's upper chambers (the atria) and lower chambers (the ventricles).

First, the electrical signal from the heart's master pacemaker, the sinoatrial (SA) node located in the atria, travels to the part of the heart that connects the atria with the ventricles, reaching another natural pacemaker known as the atroventricular (AV) node. From the AV node, the electrical signal travels down a structure called “the bundle of HIS” (sometimes referred to as the AV bundle); this is the first part of the heart's "wiring" system that conducts electrical activity into the ventricles.

The bundle of HIS enters the intraventricular septum (the wall between the heart's chambers), where it subdivides into the wire-like structures called bundle branches that carry the electrical impulse to Purkinje fibers, thin filaments that continue distributing the electrical signal to the ventricles' cells. This causes the heart to contract, pumping oxygen and nutrient-rich blood into the arteries and moving it throughout the body. But what happens if there is a glitch in the heart's complicated "wiring" system causing it to "misfire"? The result can be an abnormal heart rhythm, an arrhythmia.

Atrial Fibrillation