About Arrhythmia

Muscles must generate electricity in order to contract. For that reason, the heart has an electrical conduction system that spontaneously generates regular electrical impulses and transmits electrical signals throughout the heart. An irregular heartbeat caused by changes in or dysfunction of this system is called arrhythmia.

Arrhythmia may or may not be a sign of a serious heart disease. It may also be noticeable to the patient, or it may not be recognized. The normal adult heart rate at rest is 60 to 80 beats per minute, and a pulse rate of 60 to 100 beats per minute is considered normal. Arrhythmia refers to an abnormal heart rate or an abnormal rhythm, and it can occur anywhere in the atria or ventricles.

Arrhythmia includes two types: tachycardia, in which the heart rate is too fast, and bradycardia, in which it is too slow. Tachycardia originates in the atria or ventricles and is classified into regular tachycardia and irregular tachycardia. If tachycardia originates in the ventricles, it may progress to ventricular fibrillation, a serious condition that can cause cardiac arrest. Bradycardia includes sinus node dysfunction syndrome and complete atrioventricular block.

Most arrhythmias are caused by diseases of the heart and vascular system. During exercise or pregnancy, the heart rate increases, and very fit people may have a slower heart rate than the normal range, so a heart rate outside the normal range does not necessarily mean there is a disease. Arrhythmia reduces the mechanical pumping efficiency of the heart and decreases blood flow to the brain. The severity of arrhythmia varies depending on the type.

Causes and Risk Factors

Normal contraction of the heart requires electrical stimulation. In brief, the system is composed of the sinoatrial node, the atrioventricular node, and the bundle branches.

The sinoatrial node is located near the point where the right atrium and the superior vena cava meet, and it is where the heart's electrical rhythm begins. It is the most important site for controlling the pulse rate in healthy people. The atrioventricular node is located at the junction between the heart and the ventricles and plays an important role in transmitting electrical signals generated in the sinoatrial node to the bundle branches of the ventricles. The two bundle branches, left and right, act like wires that transmit electrical signals to the heart muscle. Therefore, when electrical generation in the heart is normal, the sinoatrial node creates electrical signals regularly, the atrioventricular node receives them, and rapidly transmits them to the bundle branches, causing both ventricles to contract almost simultaneously.

On the other hand, arrhythmia occurs when dysfunction develops in the heart's electrical conduction system itself, or when electricity is generated abnormally in a location outside this system and is conducted along a different pathway. Arrhythmia can also be triggered by changes in the heart or changes in the environment that affect the normal conduction system.

The following are causes that can trigger arrhythmia.

1. Diseases of the electrical conduction system itself: sinoatrial node dysfunction syndrome

· atrioventricular node dysfunction syndrome · the presence of an abnormal electrical conduction system

· electrical waves generated outside the normal electrical conduction system · genetic disorders

2. Changes in the heart that affect the electrical conduction system

· ischemic heart disease such as myocardial infarction · congenital heart disease · cardiomyopathy, valvular heart disease · various medications

3. Environmental changes that affect the electrical conduction system

· severe stress · caffeine · alcohol, smoking · insufficient sleep

Classification of Arrhythmia

Arrhythmia is classified according to the mechanism of onset into disorders of impulse formation, disorders of impulse conduction, and mixed disorders, and according to the site of occurrence into supraventricular and ventricular arrhythmias.

Arrhythmia is classified as follows according to the mechanism of onset, heart rate, site of occurrence, and the site where the conduction disorder occurred.

1. Disorders of impulse formation

The sinus node serves as the pacemaker that creates the heart's normal rhythm, and as the electrical rhythm of the sinus node spreads throughout the heart through the sinoatrial node, the heart performs regular pumping movements.

A disorder of impulse formation refers to a type of arrhythmia that occurs when the sinus node's electrical rhythm is not formed normally or when rhythm is formed in a location other than the sinus node.

Arrhythmias caused by disorders of impulse formation are divided into supraventricular and ventricular arrhythmias according to the site of occurrence.

1. Supraventricular arrhythmia

The atria, which make up the upper part of the heart, are divided into the left atrium and the right atrium, and the ventricles, which make up the lower part of the heart, are divided into the left ventricle and the right ventricle. Supraventricular arrhythmia refers to arrhythmia caused by disorders of electrical impulse formation in the sinus node or atria above the ventricles, as well as in the atrioventricular junction, the border area between the atria and ventricles.

(1) Sinus impulse formation disorder

This is a problem with impulse formation in the sinus node, and it includes the following types:

· Sinus tachycardia: arrhythmia caused by abnormally rapid impulse formation in the sinus node

· Sinus bradycardia: arrhythmia caused by abnormally slow impulse formation in the sinus node

· Sinus arrhythmia: arrhythmia caused by irregular impulse formation in the sinus node

· Sinus arrest or sinus pause: arrhythmia caused when impulse formation in the sinus node stops or temporarily pauses (skips)

(2) Ectopic impulse formation

This is arrhythmia caused by electrical impulses forming in a location other than the sinus node, and it is divided according to the site of occurrence into atrial impulse formation and atrioventricular junction impulse formation.

· Atrial impulse formation: ectopic impulses formed in the atria; examples include atrial premature beats, atrial tachycardia, atrial flutter, atrial fibrillation, left atrial rhythm, and multifocal atrial tachycardia.

· Atrioventricular junction impulse formation: ectopic impulses formed at the junction where the atria and ventricles meet; examples include atrioventricular junctional escape beats, atrioventricular junctional premature beats, atrioventricular junctional tachycardia, and wandering pacemaker.

2. Ventricular arrhythmia

Ventricular arrhythmia refers to arrhythmia caused by disorders of electrical impulse formation in the ventricular area that makes up the lower part of the heart. Examples include premature ventricular beats, ventricular tachycardia, polymorphic ventricular tachycardia, ventricular flutter, ventricular fibrillation, and accelerated idioventricular rhythm.

2. Disorders of impulse conduction

The heart's electrical rhythm created by the sinus node spreads throughout the heart along the conduction fibers within the heart, causing the heart to beat in sync with the sinus node's rhythm.

This type of arrhythmia refers to a condition in which, due to abnormalities in the heart's electrical signal conduction system, the heart cannot contract normally and develops arrhythmia even though the sinus node is forming a normal electrical rhythm.

(1) Sinoatrial conduction disorder: arrhythmia caused by dysfunction of conduction between the sinus node and the atria

(2) Intra-atrial conduction disorder: arrhythmia caused by dysfunction of conduction within the atria

(3) Atrioventricular conduction disorder: arrhythmia caused by dysfunction of conduction between the atria and ventricles

(4) Intraventricular conduction disorder: arrhythmia caused by dysfunction of conduction within the ventricles

3. Mixed disorders

This refers to arrhythmia that occurs when disorders of impulse formation and disorders of impulse conduction act together.

So far, I have explained arrhythmia.

In the next part, we will look at the symptoms and diagnosis of arrhythmia.

Source: Korea Disease Control and Prevention Agency, National Health Information Portal