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Heart Rhythm Disorders (Arrhythmias)

Heart Rhythm Disorders Definition and Overview

A heart rhythm disorder is an abnormal variation from the normal heartbeat. Heart rhythm disorders involve abnormalities of one or more of the following: heart rate, regularity of beats, sites where electrical impulses originate, or sequence of activation of heartbeats. Heart rhythm disorder is also referred to as an arrhythmia.

The primary function of the heart is to supply blood and nutrients to the body. The regular beating, or contraction, of the heart moves the blood throughout the body. Each heartbeat is controlled by electrical impulses traveling through the heart. In the normal heart these electrical impulses occur in regular intervals. When something goes wrong with the heart's electrical system, the heart does not beat regularly. The irregular beating results in a heart rhythm disorder, or arrhythmia.

The electrical system regulating heartbeat consists of two main areas of control that are connected to a series of conducting pathways, similar to the electrical wiring in a house.

Picture of electrical pathways of the heart.
  • The sinoatrial, or SA, node is located in the right atrium. It provides the main control and is the source of each beat. The SA node also keeps up with the body's overall need for blood and increases the heart rate when necessary, such as during exercise, emotional excitement, or illness such as fever. The SA node is sometimes called the "natural pacemaker" of the heart.
  • Electrical impulses leave the SA node and travel through special conducting pathways in the heart to the other controller, the atrioventricular, or AV, node. The purpose of the AV node is to provide a pathway for impulses from the atria to the ventricles. It also creates a delay in conduction from the atria to the ventricle. This causes the atria to contract first and allow the ventricles to fill with blood before they contract themselves.
  • The delay ensures proper timing so that the lower chambers of the heart (ventricles) have time to fill completely before they contract.

Normally, the heart beats about 60 to 100 times a minute. This state is called "normal sinus rhythm" or "normal rhythm" or "normal heartbeat." Depending upon the needs of the body, it may beat faster (sinus tachycardia) due to stress or slower (sinus bradycardia) such as during sleep.

Arrhythmias

Arrhythmias are abnormalities of the heartbeat. There are many types of arrhythmias, and they are classified by some investigators by where they begin in the heart (the atria, AV node, or the ventricles). Others classify arrhythmias as one of four types -- premature beats, supraventricular, ventricular, and bradyarrhythmias. Generally speaking, those that do not originate from the ventricles are called supraventricular arrhythmias while those that come from the ventricles are called ventricular arrhythmias. The arrhythmias that can often lead to death in minutes are ventricular fibrillation and ventricular tachycardia. Although others may also cause death, these two arrhythmias can quickly and severely alter the heart's ability to effectively pump blood. Immediate electrocardioversion to put the heart back into a more effective rhythm that allows the heart to pump blood effectively can be life-saving.

The following are some of the more commonly encountered arrhythmias, starting with the supraventricular arrhythmias.

  • Premature atrial contractions, sometimes called PAC or APC, or premature supraventricular contractions: This happens when another part of the atria sends an electrical impulse soon after the previous beat, causing the heart to contract earlier than expected. This arrhythmia is a very common occurrence in all ages and usually is not serious.
  • Supraventricular tachycardia, or paroxysmal SVT or PSVT: SVT occurs when any structure above the ventricle (usually the atria or the AV node) produces a regular, rapid electrical impulse resulting in a rapid heartbeat.
  • Sick sinus syndrome: Irregular electrical impulses generated by the SA node cause a slower-than-normal heart rate (sometimes alternating with rapid heart rates if the electrical impulses switch to a high rate).
  • Wolff-Parkinson-White (WPW) syndrome: This is an arrhythmia people are born with because they have extra electrical pathways leading from the atrium to the ventricle that can cause tachycardia and particular types of rapid arrhythmias.
  • Atrial fibrillation: This is a common condition caused by electrical impulses discharged at a rapid rate from many different areas of the atria. It usually causes a fast and irregular heartbeat.
  • Atrial flutter: This condition is caused by a rapid discharge from a single place in the right atrium. Typically, the right atrium produces electrical impulses at a rate of 300 beats per minute, but only every other beat is conducted through the AV node, meaning that the ventricular rate is classically about 150 beats per minute.
Medically Reviewed by a Doctor on 3/21/2013

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