Heart Information Center

Facts About Arrhythmias/Rhythm Disorders

Introduction Tests for Detecting Arrhythmias
What is an arrhythmia? Arrhythmia Types
What happens during an arrhythmia? What is a heart block?
Are arrhythmias serious? How are arrhythmias treated
What causes arrhythmias? How can arrhythmias be prevented?
Symptoms of an arrhythmia Glossary
How is an arrhythmia diagnosed? Other Sources of Information

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The number of times the heart beats each minute (BPM) is called the heart rate. The time from one beat to the next is about the same. The resting heart rate for a newborn is about 140 BPM, that for an older child or adolescent 70-80 BPM, and 60-70 BPM for an adult.

The heart rate can easily change. For example, exercise makes the heart speed up; during sleep it slows down. Arrhythmia's, specialized tests and treatments are discussed below.


If the heart isn't beating regularly, it has an arrhythmia. The most common, but normal, heart rhythm irregularity occurs during breathing. When a person breathes in, the heart rate normally speeds up for a few beats. It slows down again when a person breaths out. This variation with breathing is called sinus arrhythmia and is completely normal. A doctor may find irregularities that differ from a sinus arrhythmia. The heart may seem to skip a beat or beat irregularly or very fast or very slowly. Then the doctor may want to perform other tests or may recommend that the patient be seen by a cardiologist (a doctor who specializes in heart problems).

Arrhythmias can occur at any age, even in infants. They commonly in middle-age adults. As people get older, they are more likely to experience an arrhythmia.


What happens in the heart during an arrhythmia?

The normal heart is a strong, hardworking, muscular pump. A person's heart, when normal sized, is slightly larger than his or her fist. Describing how the heart beats normally helps to explain what happens during an arrhythmia.

The heart is divided into right and left sides; there's an upper and lower chamber on each side. The right and left atria (upper chambers) receive blood from the body and the lungs. The right and left ventricles (lower chambers) are the muscular chambers. They pump blood out of the heart to the lungs and body.

As blood travels through the heart, it moves through a series of valves. The valves open and close to let blood flow in only one direction.

(See animated pumping heart )

Each heartbeat begins when a specialized area of the right atrium (the sinus node or S-A node, which is also called the heart's pacemaker) generates a small amount of electricity. Each electrical signal leaves the sinus node and spreads into the muscle cells of the heart's atria. This causes them to contract (beat).

The electrical activity then moves into the junction between the atria and ventricles. There it passes through the atrioventricular node (A-V node). The A-V node acts as a relay station. It takes the signal coming from the atria, delays it slightly, then passes it into the ventricles, causing them to beat

Usually the whole heart contracts between 60 and 100 times per minute with beats spaced evenly. Each contraction equals one heartbeat. This is called normal sinus rhythm.

(See animation of heart conduction system)

An arrhythmia may occur for one of several reasons:

  • Instead of beginning in the sinus node, the heartbeat begins in another part of the heart.
  • The sinus node develops an abnormal rate or rhythm.
  • The signal bypasses the normal regulation of the AV node
  • A patient has a heart block.


Are arrhythmias serious?

Many arrhythmias occur in people who do not have underlying heart disease. The vast majority of people with arrhythmias have nothing to fear. They do not need extensive exams or special treatments for their condition.

In some people, arrhythmias are associated with heart disease. In these cases, heart disease, not the arrhythmia, poses the greatest risk to the patient.

In a very small number of people with serious symptoms, arrhythmias themselves are dangerous. These arrhythmias require medical treatment to keep the heartbeat regular. For example, a few people have a very slow (bradycardia) or fast (tachycardia) heartbeat. These patients may have symptoms such as chest pain, shortness of breath, lightheadedness or fainting because the heart is not pumping enough blood to the body. If left untreated, the heart may stop beating and these people could die.


Many times, there is no recognizable cause of an arrhythmia. Heart disease may cause arrhythmias. Extra conduction pathways (inherited) in an otherwise healthy heart may cause certain arrhythmias. Other causes include: stress, caffeine, tobacco, alcohol, diet pills, and cough and cold medicines.


Most people have felt their heart beat very fast, experienced a fluttering in their chest, or noticed that their heart skipped a beat. Almost everyone has also felt dizzy, faint, or out of breath or had chest pains at one time or another. Symptoms may include:

  • palpitations (increased awareness of the heart beating faster) This is often the only symptom for most people.
  • chest pain
  • shortness of breath
  • lightheadedness or fainting
  • fatigue or weakness

You should not panic if you experience a few flutters or your heart races occasionally. But if you have questions about your heart rhythm or symptoms, check with your doctor.


Arrhythmia's (also called dysrhythmias) may occur at any age. Sometimes a person may not be aware they have an arrhythmia.

The usual ways to evaluate a rhythm abnormality are similar to those used to evaluate other health problems. The patient's history is very important. Questions like these might be asked:

  • Are you aware of unusual heartbeats?
  • Does anything bring on the arrhythmia? What can you do, if anything, to make it stop?
  • If it's a fast rate, how fast?
  • Do you feel weak, lightheaded or dizzy?
  • Have you ever fainted?

Some medicines may make arrhythmias worse. It's important to tell the doctor about all prescribed and over-the-counter medicines that you take.


First the doctor will take a medical history and do a thorough physical exam. Then one or more tests may be used to check for an arrhythmia and to decide whether it is caused by heart disease. Sometimes an arrhythmia can be detected by listening to the heart with a stethoscope. To identify an arrhythmia, the heart's activity must be recorded on an electrocardiogram (ECG or EKG).

An arrhythmia may not occur at the time of the exam even though symptoms are present at other times. In such cases, tests will be done if necessary to find out whether an arrhythmia is causing the symptoms.

Tests for Detecting Arrhythmias

Electrocardiogram (ECG or EKG). Records the electrical activity of the heart. Each time the heart beats, it sends out an electric-like signal. An ECG machine can record this activity. To record the ECG, small patches or stickers called electrodes are placed on different parts of the body. One is put on each arm and leg and six across the chest.

With various combinations of these electrodes, different tracings of the heart's electrical activity can be made and permanently recorded on paper or in a computer. The types of ECGs are:

Resting ECG. The patient lies down for a few minutes while a record is made. In this type of ECG, disks are attached to the patient's arms and legs as well as to the chest. Records about 12 seconds of heart electrical activity.

Exercise ECG (stress test). The patient exercises either on a treadmill machine or bicycle while connected to the ECG machine. This test tells whether exercise causes arrhythmias or makes them worse or whether there is evidence of inadequate blood flow to the heart muscle ("ischemia"). Records electrical activity for duration of exercise (10 to 20 minutes).

24-hour ECG (Holter) monitoring. The patient goes about his or her usual daily activities while wearing a small, portable recorder that connects to the disks on the patient's chest. Over time, this test shows changes in rhythm (or "ischemia") that may not be detected during a resting or exercise ECG. Can record continuously for 24 to 48 hours.

Transtelephonic monitoring. The patient wears the recorder and disks over a period of a few days to several weeks. When the patient feels an arrhythmia, he or she telephones a monitoring station where the record is made. If access to a telephone is not possible, the patient has the option of activating the monitor's memory function. Later, when a telephone is accessible, the patient can transmit the recorded information from the memory to the monitoring station. Transtelephonic monitoring can reveal arrhythmias that occur only once every few days or weeks.

Electrophysiologic studies (EPS)

Intracardiac Electrophysiologic Procedure. Sometimes it's necessary to study the heart's electrical system with an intracardiac (within the heart) electrophysiologic procedure. In this, one or more long, thin tubes (catheters) are placed into the large blood vessels in the legs, arms or both. Then the tips of the catheters are moved into the heart. Once in the heart, the catheters can record electrical signals from the normal electrical system. This gives much more precise information than an ordinary ECG. During these studies, the heart can be stimulated to beat rapidly or irregularly. The heart's response to this - and the way electricity moves around the heart during a tachycardia - helps the cardiologist diagnose the nature of an arrhythmia. Sometimes abnormal tissue causing an arrhythmia is then destroyed by heating it with a probe (called radioablation therapy).

Esophageal Electrophysiologic Procedure. In some situations, your cardiologist may recommend that an esophageal electrophysiologic procedure be done. This is used to diagnose or treat the type of tachycardia you have. In this procedure, a thin, soft, flexible plastic tube is inserted into your nostril and positioned in the esophagus. (The esophagus is the tube that connects the mouth and stomach.) Since the esophagus is close to the upper chambers (atria) of the heart, an ECG recording there gives more precise information than a regular ECG. An electrical stimulator may be used to make the heart beat faster to try to restart your arrhythmia. This helps your doctor make the right diagnosis.

During this procedure certain medications may be tested to find the one that will be most effective. The esophageal electrophysiologic procedure also may be performed to temporarily stop certain types of arrhythmias. This procedure is similar, but less invasive than an intracardiac procedure. Ablation therapy (directly destroying abnormal heart conduction tissue) cannot be performed with the esophageal procedure.



What are the different types of an arrhythmias?

There are many types of arrhythmias. Arrhythmias are identified by where they occur in the heart (atria or ventricles) and by what happens to the heart's rhythm when they occur.

Arrhythmias arising in the atria are called atrial or supraventricular (above the ventricles) arrhythmias. Ventricular arrhythmias begin in the ventricles. In general, ventricular arrhythmias caused by heart disease are the most serious.

Arrhythmia Types

Originating in the Atria

  • Sinus arrhythmia
    Normal cyclic changes in the heart rate during breathing. Common in children and often found in adults.

  • Sinus tachycardia
    The sinus node sends out electrical signals faster than usual, speeding up the heart rate. A heart rate greater than 100 beats per minute.

  • Sick sinus syndrome
    Sometimes the sinus node, as well as the AV node, doesn't work properly. Different combinations of supraventricular arrhythmias, both slow and fast, are produced on an intermittent basis. This condition almost always indicates disease of multiple areas of the heart conduction system. Symptoms of sick sinus syndrome are caused by either too fast or slow heart rate and include near syncope or syncope (passing out due to not enough blood reaching the brain), chest pain, shortness of breath, palpitations and stroke.

    Holter monitoring (a device continuously recording heart electrical activity for 1-2 days) is often needed to diagnose sick sinus syndrome. A routine EKG often does not show intermittent arrhythmias common in this syndrome.

    Bradycardias causing symptoms usually require a pacemaker. Tachycardias are usually treated with medication to slow the heart rate down. Medications are usually started after pacemaker insertion because they can make bradycardias worse.
  • Premature Atrial Contraction (PAC)
    Irregular heart rhythms are most often caused by premature beats or extra beats. These originate in the upper chambers (premature atrial contraction, PAC). When we feel our heart "skip a beat," it usually results from this type of arrhythmia.

    The heart does not skip a beat. Instead an extra beat comes sooner than normal. This is followed by a pause that causes the next beat to be more forceful. The person feels this more-forceful beat.

    Premature beats are common in healthy people of all ages- most people have them at some time. Caffeine, alcohol, stress and fatigue may cause PAC's to occur more frequently. Usually no special treatment is needed and no cause can be found. The premature beats may disappear, and even if they continue, most people tolerate them well.

  • Supraventricular tachycardia (SVT)
    A series of early beats in the atria speed up the heart rate (the number of times a heart beats per minute). In paroxysmal tachycardia, repeated periods of very fast heartbeats begin and end suddenly.

    The most common abnormal tachycardia in children (and common in adults as well) is reentrant supraventricular tachycardia (SVT). It's also known as paroxysmal atrial tachycardia (PAT) or paroxysmal supraventricular tachycardia (PSVT). The fast heart rate involves both the heart's upper and lower chambers. This isn't a lifethreatening problem for most people. For many, it doesn't require medical therapy. Treatment is considered if episodes are prolonged or frequent. There are several subgroups of SVT, including Wolf-Parkinson-White syndrome (WPW). The heart rate is generally between 160-200 beats per minute which can be tolerated by most people for an extended period of time.

  • Wolff-Parkinson-White syndrome.
    A specific type of SVT this condition is caused by abnormal pathways between the atria and ventricles, causing the electrical signal to arrive at the ventricles too soon and to be transmitted back into the atria. Very fast heart rates may develop as the electrical signal ricochets between the atria and ventricles. Sometimes the heart rate can be very high (200-300 beats per minute). Some medications used to slow regular SVT down can actually make the heart beat even faster in a particular type of WPW.

  • Atrial flutter
    Rapidly fired signals cause the muscles in the atria to contract quickly, leading to a very fast (250-350 atrial beats per minute) and regular heartbeat. There is normally a conduction block at the AV node. That is for any given number of atrial beats reaching the AV node a certain number are blocked. Usually one ventricular beat occurs for every two atrial impulses reaching the AV node. Sometimes 3:1 or even higher block occurs ( that is for every three atrial impulses reaching the AV node one is conducted through to the ventricles).

    Atrial flutter almost always occurs in patients with underlying heart disease. Atrial flutter is sometimes seen as a transition rhythm between atrial fibrillation and normal sinus rhythm.

  • Atrial fibrillation.
    Electrical signals in the atria are fired in a very fast and uncontrolled manner. Atrial signals are rapid and chaotic beating upto 400 beats per minute. Instead of a single electrical signal followed by coordinated atrial contraction there is quivering of the atrial muscle. Not all signals are conducted through the AV node. Heart rates may vary from 100 to 180. Irregular beats (unevenly spaced) heart beats always occur with atrial fibrillation. (Heart beats are very fast but regular in PSVT). Atrial fibrillation can occur in a sustained manner or may occur episodically.

    The atria do not effectively pump blood. Because most of the blood filling the ventricles does not require atrial pumping (blood flows passively into the ventricles from the atria during the heart's rest cycle) most people still have enough blood flow to the body's organs. Atrial fibrillation is usually due to atrial dilatation and associated with four conditions :

    • overactive thyroid (Hyperthyroidism)
    • rheumatic heart disease
    • prolonged high blood pressure
    • ischemic heart disease (coronary artery disease)
    • It may infrequently occur in young to middle aged healthy people.

    It is important for your doctor to know is you have atrial fibrillation because of increased risk of stroke. Small emboli ( blood clots) are more likely to form in the atria because blood does not move as well. When these emboli break loose they may travel to the brain or other organs.

Originating in the Ventricles

  • Premature ventricular complexes (PVC) An electrical signal from the ventricles causes an early heart beat that generally goes unnoticed. The heart then seems to pause until the next beat of the ventricle occurs in a regular fashion. Premature beats are common in healthy people of all ages- most people have them at some time. Usually no special treatment is needed and no cause can be found. The premature beats may disappear, and even if they continue, most people tolerate them well. Occasionally PVC's may be caused by disease or injury to the heart.

  • Ventricular tachycardia (VT) .
    The heart beats fast due to electrical signals arising from the ventricles (rather than from the atria). It's a potentially serious condition that could threaten a person's life. Heart rate ranges from 150 to 200 beats per minute. Certain medications can make this condition worse.

    VT almost always results from serious heart disease such as coronary artery disease and acute heart attacks; it usually requires prompt treatment. Ventricular tachycardia, rare in children, occurs more frequently as people age. Often specialized tests, including an intracardiac electrophysiologic procedure (see Special Tests), may be needed to evaluate the tachycardia and the effect of drug treatment. Some forms of VT may not need treatment.

  • Ventricular fibrillation.
    Electrical signals in the ventricles are fired in a very fast and uncontrolled manner, causing the heart to quiver rather than beat and pump blood. This is the rhythm responsible for "shocking" unconscious people on television shows. The ventricle "quivers" with no effective pumping of blood. The heart has not actually stopped. Because the heart does not pump blood to the body a person in ventricular fibrillation loses consciousness immediately.

    VF is almost always seen in patients with severe coronary artery disease. Much less commonly it may occur in younger people with normal coronary arteries who have certain inherited heart conditions and in people who have had the heart muscle or conduction system injured by infection (myocarditis). VF may also occur with a very hard blow to the chest, abnormal concentrations of certain minerals in the body, too low a body temperature (hypothermia), and when the amount of certain medications in the body is too high.

    Electrical cardioversion, using DC current, is always the first treatment. With an electrical shock, it immediately disrupts a deadly arrhythmia. To have any chance of recovery cardioversion must be done quickly. CPR is started if cardioversion unsuccessful after 3 consecutive attempts.

Cardiac Standstill (Asystole)

Is the complete absence of heart electrical activity. This is often a terminal arrhythmia usually causing death. That is other arrhythmias, such as ventricular fibrillation, progress to asystole if not treated. The heart does not pump or even quiver.



What is a heart block?

Heart block is a condition in which the electrical signal cannot travel normally down the special pathways to the ventricles. It doesn't mean the blood flow is blocked; it means that the flow of the electrical signal within the heart is blocked. For example, the signal from the atria to the ventricle may be (1) delayed, but each one conducted; (2) delayed with only some getting through; or (3) completely interrupted. If there is no conduction, the beat generally originates from the ventricles and is very slow.


Many arrhythmias require no treatment . Serious arrhythmias are treated in several ways depending on what is causing the arrhythmia. Sometimes the heart disease is treated to control the arrhythmia. Or, the arrhythmia itself may be treated using one or more of the following treatments.

There are several kinds of drugs used to treat arrhythmias. One or more drugs may be used. Drugs are carefully chosen because they can cause side effects. In some cases, they can cause arrhythmias or make arrhythmias worse. For this reason, the benefits of the drug are carefully weighed against any risks associated with taking it. It is important not to change the dose or type of your medication unless you check with your doctor first.

If you are taking drugs for an arrhythmia, one of the following tests will probably be used to see whether treatment is working: a 24-hour electrocardiogram (ECG) while you are on drug therapy, an exercise ECG, or a special technique to see how easily the arrhythmia can be caused. Blood levels of antiarrhythmic drugs may also be checked.

To quickly restore a heart to its normal rhythm, the doctor may apply an electrical shock to the chest wall. Called cardioversion, this treatment is most often used in emergency situations involving potentially life threatening problems, such as very low blood pressure or decreased level of consciousness, or in patients who have repeatedly failed to respond to medication. After cardioversion, drugs are usually prescribed to prevent the arrhythmia from recurring.

Automatic implantable defibrillators
These devices are used to correct serious ventricular arrhythmias that can lead to sudden death. The defibrillator is surgically placed inside the patient's chest. There, it monitors the heart's rhythm and quickly identifies serious arrhythmias. With an electrical shock, it immediately disrupts a deadly arrhythmia.

Artificial pacemaker
An artificial pacemaker can take charge of sending electrical signals to make the heart beat if the heart's natural pacemaker is not working properly or its electrical pathway is blocked. It works by sending small, painless amounts of electricity to the heart to make it beat. During a simple operation, this small electrical device is placed under the skin. A lead extends from the device to the right side of the heart, where it is permanently anchored.

A variety of rhythm disorders can be successfully controlled with an artificial pacemaker. Slow heart rates, such as heart block, are the most common reason to use a pacemaker. However, new technology now lets doctors treat some fast heart rates with a pacemaker.

Radiofrequency Catheter Ablation and Surgery
Some tachycardias are lifethreatening or significantly interfere with normal activities. Permanent treatment is often needed for these problems.

One procedure, called radiofrequency catheter ablation, is done with several catheters in the heart. This is called an electrical physiologic study (EPS testing) and requires a cardiologist with specialized training as well as special equipment.

This therapy involves threading an electrode into the heart through a large central vein and electrically locating the abnormal conduction tract. Once the location of the bypass tract is known another catheter is positioned directly over the area that's causing the tachycardia. Its tip is heated and that small area of the heart is altered so that electrical current won't pass through the tissue.

Surgery that interrupts the abnormal connection in the heart is another treatment.

How can arrhythmias be prevented?

If heart disease is not causing the arrhythmia, the doctor may suggest that you avoid what is causing it. For example, if caffeine or alcohol is the cause, the doctor may ask you not to drink coffee, tea, colas, or alcoholic beverages.



Arrhythmia An irregularity in heart beat
Atria Upper two heart chambers. Right atria delivers blood to right ventricle. Left atria delivers blood to left ventricle.
Atrioventricular node (AV node) Special conduction tissue that relays electrical impulses from the atria to ventricles
Asystole Complete absence of heart electrical and pumping activity
Bradycardia Heart rate less than 60
Cardiopulmonary resuscitation (CPR) A combination of chest compressions and assisted breathing performed when a the electrical and pumping function of a person's heart is not working. Typically performed when the heart in ventricular fibrillation or asystole.
Cardioversion DC electrical current used to stop certain arrhythmias by resynchronizing the hearts electrical activity.
Electrocardiogram (EKG or ECG) A machine capable of measuring the electrical activity of various parts of the heart
Heart disease Generally, injury to heart muscle and/or conducting system due to decreased blood flow from coronary artery disease.
Heart rate Number of time a minute the heart contracts
Implantable defibrillator A device surgically placed in a patient's chest wall or abdomen that is capable of recognizing unstable arrhythmias and delivering DC electrical current (cardioversion) to stop the arrhythmia
Myocarditis Inflammation or infection (usually viral) of the heart muscle
Pacemaker An artificial pacemaker can take charge of sending electrical signals to make the heart beat if the heart's natural pacemaker is not working properly or its electrical pathway is blocked.
Sinoatrial node (SA node) The normal pacemaker tissue that generates electrical impulses traveling to and causing atria and ventricles to contract
Sinus Arrhythmia Normal variation in heart rate due to breathing cycle.
Sinus rhythm An electrical impulse generated in the SA node that maintains a heart rate between 60 and 100 and is regular.
Tachycardia A heart rate above 100 beats per minute
Ventricle Lower 2 pumping chambers of the heart. Right ventricle pumps blood to the lungs to be oxygenated. Left ventricle pumps oxygenated blood to the body



Other sites/references

To obtain publications about heart disease, you may contact your:

  • local American Heart Association chapter.
  • local or state health department.
  • your personal physician
  • National Heart, Lung, and Blood Institute also has publications about heart disease.

Questions or comments?

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