Arrhythmias

Arrhythmias

What is an arrhythmia?

An arrhythmia (also referred to as dysrhythmia) is an abnormal rhythm of the heart, which can cause the heart to pump less effectively.

Arrhythmias can cause problems with contractions of the heart chambers by:

In any of these situations, the body's vital organs may not receive enough blood.

What are the symptoms of arrhythmias?

The effects on the body are often the same, however, whether the heartbeat is too fast, too slow, or too irregular. Some symptoms of arrhythmias include, but are not limited to:

The symptoms of arrhythmias may resemble other conditions. Consult your doctor for a diagnosis.

To better understand arrhythmias, is it helpful to understand the heart's electrical conduction system.

Anatomy of the heart, view of the electrical system
Click Image to Enlarge

The heart's electrical system

The heart is, in the simplest terms, a pump made up of muscle tissue. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of the various chambers of the heart.

How does the heart beat?

An electrical stimulus is generated by the sinus node (also called the sinoatrial node, or SA node), consisting of a small mass of specialized tissue located in the right atrium (right upper chamber) of the heart. The sinus node generates a regular electrical stimulus, which for adults, is usually 60 to 100 times per minute under normal conditions. This electrical stimulus travels down through the conduction pathways (similar to the way electricity flows through power lines from the power plant to your house) and causes the heart's lower chambers to contract and pump out blood. The right and left atria (the two upper chambers of the heart) are stimulated first and contract a short period of time before the right and left ventricles (the two lower chambers of the heart).

The electrical impulse travels from the sinus node to the atrioventricular node (also called AV node), where impulses are slowed down for a very short period, then allowed to continue down the conduction pathway via an electrical channel called the bundle of His into the ventricles. The bundle of His divides into right and left pathways to provide electrical stimulation to the right and left ventricles. Each contraction of the ventricles represents one heartbeat.

Each day the heart beats about 100,000 times, on average. Any dysfunction in the heart's electrical conduction system can make the heartbeat too fast, too slow, or at an uneven rate, thus, causing an arrhythmia.

What is an electrocardiogram (ECG)?

The electrical activity of the heart is measured by an electrocardiogram (ECG or EKG). By placing electrodes at specific locations on the body (chest, arms, and legs), a graphic representation, or tracing, of the electrical activity can be obtained. Changes in an ECG from the normal tracing can indicate arrhythmias, as well as other heart-related conditions.

What does an ECG mean?

Illustration of a basic EKG tracing
Click Image to Enlarge

Almost everyone knows what a basic ECG tracing looks like. But what does it mean?

When your doctor studies your ECG, he/she looks at the size and length of each part of the ECG. Variations in size and length of the different parts of the tracing may be significant. The tracing for each lead of a 12-lead ECG will look different, but will have the same basic components as described above. Each lead of the 12-lead is "looking" at a specific part of the heart, so variations in a lead may indicate a problem with the part of the heart associated with the lead.

What are the different types of arrhythmias?

An atrial arrhythmia is caused by abnormal function of the sinus node or the atrialventricular node, or by the development of another atrial pacemaker within the atrium that takes over the function of the sinus node.

A ventricular arrhythmia is caused by abnormal electrical focus within the ventricles, resulting in abnormal conduction of electrical signals within the ventricles. The sinus node and atrialventricular node may function normally.

Listed below are some of the more common arrhythmias:

Atrial arrhythmias

Ventricular arrhythmias

Sinus arrhythmia. A condition in which the heart rate varies with breathing. Sinus arrhythmia is commonly found in children; adults may often have it as well. This a benign (not dangerous) condition. Premature ventricular contractions (PVCs). A condition in which an electrical signal originates in the ventricles and causes the ventricles to contract before receiving the electrical signal from the atria. PVCs are common and typically do not cause symptoms or problems. However, if the frequency of the PVCs increases significantly, symptoms, such as weakness, fatigue, dizziness, fainting, or palpitations may be experienced.
Sinus tachycardia. A condition in which the heart rate is faster than normal because the sinus node is sending out electrical impulses at a rate faster than usual. Most commonly, sinus tachycardia occurs as a normal response for the heart to exercise when the heart rate increases to cope with increased energy requirements. Sinus tachycardia can be completely appropriate and normal, such as when a person is exercising vigorously. Sinus tachycardia is often temporary, also occurring when the body is under stress from strong emotions, infection, fever, hyperthyroidism, or dehydration, to name a few causes. It may cause symptoms such as weakness, fatigue, dizziness, or palpitations if the heart rate becomes too fast to pump an adequate supply of blood to the body. Once the stress is removed, the heart rate will return to its usual rate. Ventricular tachycardia (VT). A potentially life-threatening condition in which an electrical signal is sent from the ventricles at a very fast, but often regular rate. If the heart rate is sustained at a high rate for more than 30 seconds, symptoms, such as weakness, fatigue, dizziness, fainting, or palpitations, may be experienced. A person in VT may require an electric shock or medication& to convert the rhythm back to normal sinus rhythm.
Sick sinus syndrome. A condition in which the sinus node sends out electrical signals either too slowly or too fast. There may be alternation between too-fast and too-slow rates. This condition may cause symptoms if the rate becomes too slow or too fast for the body to tolerate. Ventricular fibrillation (VF). A condition in which many electrical signals are sent from the ventricles at a very fast and erratic rate. As a result, the ventricles are unable to fill with blood and pump. This rhythm is life-threatening because there is no pulse and complete loss of consciousness. A person in VF requires prompt defibrillation to restore the normal rhythm and function of the heart. It will result in sudden cardiac death if not treated within seconds
Premature supraventricular contractions or premature atrial contractions (PAC). A condition in which an atrial pacemaker site above the ventricles sends out an electrical signal early. The ventricles are usually able to respond to this signal, but the result is an irregular heart rhythm, which is typically benign. PACs are common and may occur as the result of stimulants such as coffee, tea, alcohol, cigarettes, or medications.  
Supraventricular tachycardia (SVT). A condition in which the heart rate speeds up due to a series of early beats from an atrial or junctional pacemaker site above the ventricles. There are several different forms of SVT arrhythmias. A couple of the more common examples include arrhythmias caused by an abnormal electrical connection between the top and bottom chambers of the heart such as atrioventriclar node reentry tachycardia also referred to as paroxysmal SVT, or atrioventricular reentry tachycardia with an accessory pathway sometimes referred to as Wolff-Parkinson-White Syndrome. Another common SVT form can be caused by an irritated site in the atria that fires rapidly called atrial tachycardia. SVT arrhythmias usually begin and end rapidly, occurring in repeated periods. These arrhythmias can cause symptoms, such as weakness, fatigue, dizziness, fainting, or palpitations if the heart rate becomes too fast.  
Atrial flutter. A condition in which the electrical signals come from the atria at a fast but regular rate, often causing the ventricles to contract faster and increase the heart rate. When the signals from the atria are coming at a faster rate than the ventricles can respond to, the ECG pattern develops a signature "sawtooth" pattern, showing two or more flutter waves between each QRS complex. The number of waves between each QRS complex is expressed as a ratio, i.e., a two-to-one atrial flutter means that two waves are occurring between each QRS.  
Atrial fibrillation. A condition in which the electrical signals come from the atria at a very fast and erratic rate. The ventricles contract in an irregular manner because of the erratic signals coming from the atria.  

The symptoms of various arrhythmias may resemble other medical conditions. Consult your doctor for a diagnosis.

How are arrhythmias diagnosed?

There are several different types of procedures that may be used to diagnose arrhythmias. Some of these procedures include the following:

>The ECG test has several variations:

Illustration of a man wearing a Holter monitor
Click Image to Enlarge

How are arrhythmias treated?

Some arrhythmias may be present but cause few, if any, problems. In this case, the doctor may elect not to treat the arrhythmia. However, when the arrhythmia causes symptoms, there are several different options for treatment. The doctor will choose an arrhythmia treatment based on the type of arrhythmia, the severity of symptoms being experienced, and the presence of other conditions (diabetes, kidney failure, heart failure, etc.) which can affect the course of the treatment.

Some treatments for arrhythmias include:

Click here to view the
Online Resources of Cardiovascular Disease

 

Top of Page return to top of page