Health Library

Arrhythmias

What is an arrhythmia?

An arrhythmia is an abnormal heart rhythm.

Some arrhythmias can cause problems with contractions of the heart chambers by:

  • Not allowing the ventricles (lower chambers) to fill with an adequate amount of blood because an abnormal electrical signal is causing the heart to pump too fast or too slow.

  • Not allowing a sufficient amount of blood to be pumped out to the body because an abnormal electrical signal is causing the heart to pump too slowly or too irregularly.

  • Not allowing the top chambers to work properly. 

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

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:

  • Palpitations (a sensation of fluttering or irregularity of the heartbeat) 

  • Weakness

  • Fatigue

  • Low blood pressure

  • Dizziness

  • Fainting

  • Heart failure

  • Collapse and cardiac arrest

  • Difficulty feeding (in babies)

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.

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?

Illustration of a cross section of the heart and electrical pathways. Inset box shows normal heart rhythm
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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 abnormality 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?

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

  • The first little upward notch of the ECG tracing is called the "P wave." The P wave indicates that the atria (the two upper chambers of the heart) are electrically stimulated. This causes them to contract and pump blood to the ventricles.

  • The delay in the conduction of the electrical signal from the atria to the ventricles from the beginning of the P wave to the R (or Q) wave is known as the PR interval.

  • The next part of the tracing is a short downward section connected to a tall upward section. This part is called the "QRS complex." This part indicates that the ventricles (the two lower chambers of the heart) are electrically stimulated (undergo depolarization) to pump out blood to the body via the aorta or to the lungs via the pulmonary artery. 

  • The next short flat segment is called the "ST segment." The ST segment is a time when the ventricles are activated and the electrical signal for ventricular contraction is completed.

  • The next upward curve is called the "T wave." The T wave is the electrical recovery period of the ventricles (ventricular repolarization). After the ventricles repolarize, they can then depolarize again. 

When your doctor studies your ECG, he or she looks at the size, length, and appearance 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 arrhythmia can occur in the sinus node, the atria, or the atrioventricular node. These are supraventricular arrhythmias.

A ventricular arrhythmia is caused by an abnormal electrical focus within the ventricles, resulting in abnormal conduction of electrical signals within the ventricles.

 Arrhythmias can also be classified as slow (bradyarrhythmia) or fast (tachyarrhythmia). "Brady-" means slow, while "tachy-" means fast.

Listed below are some of the more common arrhythmias:

Atrial arrhythmias

Ventricular arrhythmias

Sinus arrhythmia. A common condition in which the heart rate varies with breathing. Sinus arrhythmia is commonly found in children; adults may often have it as well. This is 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. Heart failure may develop. 

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 of 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. Cardiac arrest may occur. A person in VT may require an electric shock or medications to convert the rhythm back to normal sinus rhythm. 

Sick sinus syndrome. A condition in which the sinus node sends out electrical signals too slowly. There may be alternation between too-fast and too-slow rates (tachy brady syndrome). This condition may cause symptoms if the rate becomes too slow 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 abnormal tissue 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 atrioventricular node reentry tachycardia also referred to as paroxysmal SVT, or atrioventricular reentry tachycardia due to an extra conduction pathway between the atria and the ventricles. If that pathway conducts signals from the atria to the ventricles, it is known as Wolff-Parkinson-White Syndrome. Another common SVT form can be caused by a site in the atria that fires rapidly called atrial tachycardia. SVT usually begins and ends 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. They can cause shortness of breath or chest discomfort.

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 typically (but not always) 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, for example, 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 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 that activate the AV node. 

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:

  • Electrocardiogram (ECG or EKG). An electrocardiogram is a measurement of the electrical activity of the heart. 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 as the electrical activity is received and interpreted by an ECG machine. An ECG can indicate the presence of arrhythmias, damage to the heart caused by ischemia (lack of oxygen to the heart muscle) or myocardial infarction (MI, or heart attack), a problem with one or more of the heart valves, or other types of heart conditions.

There are several variations of the ECG test:

  • Resting ECG. For this procedure, the clothing on the upper body is removed and small sticky patches called electrodes are attached to the chest, arms, and legs. These electrodes are connected to the ECG machine by wires. The ECG machine is then started and records the heart's electrical activity for a minute or so. The patient is lying down during this ECG.

  • Exercise ECG, or stress test. The patient is attached to the ECG machine as described above. However, rather than lying down, the patient exercises by walking on a treadmill or pedaling a stationary bicycle while the ECG is recorded. This test is done to assess changes in the ECG during stress, such as exercise.

  • Signal-averaged ECG. This procedure is done in the same manner as a resting ECG, except that the heart's electrical activity is recorded over a longer period of time, usually 15 to 20 minutes. Signal-averaged ECGs are done when arrhythmia is suspected but not seen on a resting ECG. The signal-averaged ECG has increased sensitivity to abnormal ventricular activity called "late potentials." Signal-averaged ECG is used in research and seldom used in clinical practice.

  • Electrophysiologic studies (EPS). A test in which a small, thin tube (catheter) is inserted in a large blood vessel in the leg or arm and advanced to the heart. This gives the doctor the capability of finding the site of the arrhythmia's origin within the heart tissue, thus determining how to best treat it. Sometimes an attempt to treat the arrhythmia may be made by doing an ablation at the time of the study. 

  • Holter monitor. A continuous ECG recording done over a period of 24 or more hours. Electrodes are attached to the patient's chest and connected to a small portable ECG recorder by lead wires. The patient goes about his or her usual daily activities (except for activities such as taking a shower, swimming, or any activity causing an excessive amount of sweating that would cause the electrodes to become loose or fall off) during this procedure. Holter monitoring may be done when an arrhythmia is suspected but not seen on a resting ECG, since arrhythmias may be transient in nature and not seen during the shorter recording times of the resting ECG.

  • Event monitor. This is similar to a Holter monitor, but the ECG is recorded only when the patient starts the recording when symptoms are felt. Event monitors are typically worn longer than Holter monitors. The monitor can be removed to allow for showering or bathing. 

  • Mobile cardiac monitoring. This is similar to both a Holter and event monitor. The ECG is monitored constantly to allow for detection of arrhythmias, which are recorded and sent to your doctor regardless of whether symptoms are experienced. Recordings can also be initiated by the patient when symptoms are felt. These monitors can be worn up to 30 days. 

Illustration showing a male torso. Leads are attached to his chest. They are connected to a holter monitor that is clipped to the waistband of his pants.
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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 (such as, diabetes, kidney failure, or heart failure) which can affect the course of the treatment.

Some treatments for arrhythmias include:

  • Lifestyle modification. Factors, such as stress, caffeine, or alcohol, can cause arrhythmias. The doctor may order the elimination of caffeine, alcohol, or any other substances believed to be causing the problem. If stress is suspected as a cause, the doctor may recommend stress-reduction measures, such as meditation, stress-management classes, an exercise program, or psychotherapy.

  • Medication. There are various types of medications that may be used to treat arrhythmias. If the doctor chooses to use medication, the decision of which medication to use will be determined by the type of arrhythmia, other conditions which may be present, and other medications already being taken by the patient.

  • Cardioversion. In this procedure, an electrical shock is delivered to the heart through the chest to stop certain very fast arrhythmias such as atrial fibrillation, supraventricular tachycardia, or atrial flutter. The patient is connected to an ECG monitor which is also connected to the defibrillator. The electrical shock is delivered at a precise point during the ECG cycle to convert the rhythm to a normal one.

  • Ablation. This is an invasive procedure done in the electrophysiology laboratory, which means that a catheter (a very thin, flexible hollow tube) is inserted into the heart through a vessel in the groin or arm. The procedure is done in a manner similar to the electrophysiology studies (EPS) described above. Once the site of the arrhythmia has been determined by EPS, the catheter is moved to the site. By use of a technique, such as radiofrequency ablation (very high frequency radio waves are applied to the site, heating the tissue until the site is destroyed) or cryoablation (an ultra-cold substance is applied to the site, freezing the tissue and destroying the site), the site of the arrhythmia may be destroyed.

  • Pacemaker. A permanent pacemaker is a small device that is implanted under the skin (most often in the shoulder area just under the collar bone), and sends electrical signals to start or regulate a slow heart beat. A permanent pacemaker may be used to make the heart beat if the heart's natural pacemaker (the SA node) is not functioning properly and has developed an abnormal heart rate or rhythm or if the electrical pathways are blocked. Pacemakers are typically used for slow arrhythmias such as sinus bradycardia, sick sinus syndrome, or heart block.

  • Implantable cardioverter defibrillator. An implantable cardioverter defibrillator (ICD) is a small device, similar to a pacemaker, that is implanted under the skin, often in the shoulder area just under the collarbone. An ICD senses the rate of the heartbeat. When the heart rate exceeds a rate programmed into the device, it delivers an electrical shock to the heart in order to correct the rhythm to a slower more normal heart rhythm. ICDs are combined with a pacemaker to deliver an electrical signal to regulate a heart rate that is too slow. ICDs are used for life-threatening fast arrhythmias such as ventricular tachycardia or ventricular fibrillation.

  • Surgery. Surgical treatment for arrhythmias is usually done only when all other appropriate options have failed. Surgical ablation is a major surgical procedure requiring general anesthesia. The chest is opened, exposing the heart. The site of the arrhythmia is located, the tissue is destroyed or removed in order to eliminate the source of the arrhythmia.