The HeartCheck™ Learning Centre
Information Taken from the National Blood Heart and Lung Institute website
What Is an Electrocardiogram?
An electrocardiogram (e-lek-tro-KAR-de-o-gram), also called an EKG or ECG, is a simple, painless test that records the heart's electrical activity. To understand this test, it helps to understand how the heart works.
With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As it travels, the signal causes the heart to contract and pump blood. The process repeats with each new heartbeat.
The heart's electrical signals set the rhythm of the heartbeat. For more detailed information and animations, go to the Diseases and Conditions Index How the Heart Works article.
An EKG shows the following:
- How fast your heart is beating
- Whether the rhythm of your heartbeat is steady or irregular
- The strength and timing of electrical signals as they pass through each part of your heart
Doctors use EKGs to detect and study many heart problems, such as heart attacks, arrhythmias (ah-RITH-me-ahs), and heart failure. The test's results also can suggest other disorders that affect heart function.
Who Needs an Electrocardiogram?
Your doctor may recommend an electrocardiogram (EKG) if you have signs or symptoms that suggest a heart problem. Examples of such signs and symptoms include:
- Chest pain
- Heart pounding, racing, or fluttering, or the sense that your heart is beating unevenly
- Breathing problems
- Tiredness and weakness
- Unusual heart sounds when your doctor listens to your heartbeat
You may need to have more than one EKG so your doctor can diagnose certain heart conditions.
An EKG also may be done as part of a routine health exam. The test can screen for early heart disease that has no symptoms. Your doctor is more likely to look for early heart disease if your mother, father, brother, or sister had heart disease—especially early in life.
You may have an EKG so your doctor can check how well heart medicine or a medical device, such as a pacemaker, is working. The test also may be used for routine screening before major surgery.
Your doctor also may use EKG results to help plan your treatment for a heart condition
What To Expect Before an Electrocardiogram
You don't need to take any special steps before having an electrocardiogram (EKG). However, tell your doctor or his or her staff about the medicines you're taking. Some medicines can affect EKG results.
What Does an Electrocardiogram Show?
Many heart problems change the heart's electrical activity in distinct ways. An electrocardiogram (EKG) can help detect these heart problems.
EKG recordings can help doctors diagnose heart attacks that are in progress or have happened in the past. This is especially true if doctors can compare a current EKG recording to an older one.
An EKG also can show:
- Lack of blood flow to the heart muscle (coronary heart disease)
- A heartbeat that's too fast, too slow, or irregular (arrhythmia)
- A heart that doesn't pump forcefully enough (heart failure)
- Heart muscle that's too thick or parts of the heart that are too big (cardiomyopathy)
- Birth defects in the heart (congenital heart defects)
- Problems with the heart valves (heart valve disease)
- Inflammation of the sac that surrounds the heart (pericarditis)
An EKG can reveal whether the heartbeat starts in the correct place in the heart. The test also shows how long it takes for electrical signals to travel through the heart. Delays in signal travel time may suggest heart block or long QT syndrome.
What Is an Arrhythmia?
An arrhythmia (ah-RITH-me-ah) is a problem with the rate or rhythm of the heartbeat. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm.
A heartbeat that is too fast is called tachycardia (TAK-ih-KAR-de-ah). A heartbeat that is too slow is called bradycardia (bray-de-KAR-de-ah).
Most arrhythmias are harmless, but some can be serious or even life threatening. When the heart rate is too fast, too slow, or irregular, the heart may not be able to pump enough blood to the body. Lack of blood flow can damage the brain, heart, and other organs.
Types of Arrhythmia
The four main types of arrhythmia are premature (extra) beats, supraventricular arrhythmias, ventricular arrhythmias, and bradyarrhythmias (bray-de-ah-RITH-me-ahs).
Premature (Extra) Beats
Premature beats are the most common type of arrhythmia. They're harmless most of the time and often don't cause any symptoms.
When symptoms do occur, they usually feel like fluttering in the chest or a feeling of a skipped beat. Most of the time, premature beats need no treatment, especially in healthy people.
Premature beats that occur in the atria are called premature atrial contractions, or PACs. Premature beats that occur in the ventricles are called premature ventricular contractions, or PVCs.
In most cases, premature beats occur naturally, not due to any heart disease. But certain heart diseases can cause premature beats. They also can happen because of stress, too much exercise, or too much caffeine or nicotine.
Supraventricular arrhythmias are tachycardias (fast heart rates) that start in the atria or the atrioventricular (AV) node. The AV node is a group of cells located between the atria and the ventricles.
Types of supraventricular arrhythmias include atrial fibrillation (AF), atrial flutter, paroxysmal supraventricular tachycardia (PSVT), and Wolff-Parkinson-White (WPW) syndrome.
AF is the most common type of serious arrhythmia. It's a very fast and irregular contraction of the atria.
In AF, the heart's electrical signal doesn't begin in the SA node. Instead, the signal begins in another part of the atria or in the nearby pulmonary veins and is conducted abnormally.
When this happens, the electrical signal doesn't travel through the normal pathways in the atria. Instead, it spreads throughout the atria in a fast and disorganized manner.
This causes the walls of the atria to quiver very fast (fibrillate) instead of beating normally. As a result, the atria aren't able to pump blood into the ventricles the way they should.
The animation below shows atrial fibrillation. Click the "start" button to play the animation. Written and spoken explanations are provided with each frame. Use the buttons in the lower right corner to pause, restart, or replay the animation, or use the scroll bar below the buttons to move through the frames.
The animation shows how the heart's electrical signal starts in a place in the right atrium other than the sinoatrial node, causing the atria to beat very fast and irregularly.
In AF, electrical signals can travel through the atria at a rate of more than 300 per minute. Some of these abnormal electrical signals can travel to the ventricles, causing them to beat too fast and with an irregular rhythm. AF usually isn't life threatening, but it can be dangerous when it causes the ventricles to beat very fast.
The two most serious complications of chronic (long-term) AF are stroke and heart failure. Stroke can happen if a blood clot travels to an artery in the brain, blocking off blood flow.
In AF, blood clots can form because some of the blood "pools" in the fibrillating atria instead of flowing into the ventricles. If a piece of a blood clot in the left atrium breaks off, it can travel to the brain, causing a stroke. People who have AF often are treated with blood-thinning medicines to lower their risk for blood clots.
Heart failure is when the heart can't pump enough blood to meet the body's needs. AF can cause heart failure if the ventricles beat too fast and don't have enough time to fill with blood to pump out to the body. Heart failure causes fatigue (tiredness), leg swelling, and shortness of breath.
AF and other supraventricular arrhythmias can occur for no apparent reason. But most of the time, an underlying condition that damages the heart muscle and its ability to conduct electrical impulses causes AF. These conditions include high blood pressure, coronary heart disease (also called coronary artery disease), heart failure, and rheumatic heart disease.
Other conditions also can lead to AF, including an overactive thyroid gland (too much thyroid hormone produced) and heavy alcohol use. AF also becomes more common as people get older.
Atrial flutter is similar to AF, but instead of the electrical signals spreading through the atria in a fast and irregular rhythm, they travel in a fast and regular rhythm.
Atrial flutter is much less common than AF, but it has similar symptoms and complications.
Paroxysmal Supraventricular Tachycardia
PSVT is a very fast heart rate that begins and ends suddenly. PSVT occurs due to problems with the electrical connection between the atria and the ventricles.
In PSVT, electrical signals that begin in the atria and travel to the ventricles can reenter the atria, causing extra heartbeats. This type of arrhythmia usually isn't dangerous and tends to occur in young people. It can happen during vigorous exercise.
A special type of PSVT is called Wolff-Parkinson-White syndrome. WPW syndrome is a condition in which the heart's electrical signals travel along an extra pathway from the atria to the ventricles.
This extra pathway disrupts the timing of the heart's electrical signals and can cause the ventricles to beat very fast. This type of arrhythmia can be life threatening.
The animation below shows Wolff-Parkinson-White syndrome. Click the "start" button to play the animation. Written and spoken explanations are provided with each frame. Use the buttons in the lower right corner to pause, restart, or replay the animation, or use the scroll bar below the buttons to move through the frames.
The animation shows how an extra, abnormal electrical pathway in the heart disrupts the normal timing of the heart's electrical signal, causing the atria and ventricles to beat too fast.
These arrhythmias start in the ventricles. They can be very dangerous and usually need medical attention right away.
Ventricular arrhythmias include ventricular tachycardia and ventricular fibrillation (v-fib). Coronary heart disease, heart attack, weakened heart muscle, and other problems can cause ventricular arrhythmias.
Ventricular tachycardia is a fast, regular beating of the ventricles that may last for only a few seconds or for much longer.
A few beats of ventricular tachycardia often don't cause problems. However, episodes that last for more than a few seconds can be dangerous. Ventricular tachycardia can turn into other, more dangerous arrhythmias, such as v-fib.
V-fib occurs when disorganized electrical signals make the ventricles quiver instead of pump normally. Without the ventricles pumping blood out to the body, you'll lose consciousness within seconds and die within minutes if not treated.
To prevent death, the condition must be treated right away with an electric shock to the heart called defibrillation (de-fib-ri-LA-shun).
V-fib may happen during or after a heart attack or in someone whose heart is already weak because of another condition. Health experts think that most of the sudden cardiac deaths that occur every year (about 335,000) are due to v-fib.
The animation below shows ventricular fibrillation. Click the "start" button to play the animation. Written and spoken explanations are provided with each frame. Use the buttons in the lower right corner to pause, restart, or replay the animation, or use the scroll bar below the buttons to move through the frames.
The animation shows how disorganized electrical signals in the heart's ventricles can cause them to pump abnormally and quiver.
Torsades de pointes (torsades) is a type of v-fib that causes a unique pattern on an EKG (electrocardiogram). Certain medicines or imbalanced amounts of potassium, calcium, or magnesium in the bloodstream can cause this condition.
People who have long QT syndrome are at higher risk for torsades. People who have this condition need to be careful about taking certain antibiotics, heart medicines, and over-the-counter medicines.
Bradyarrhythmias are arrhythmias in which the heart rate is slower than normal. If the heart rate is too slow, not enough blood reaches the brain. This can cause you to lose consciousness.
In adults, a heart rate slower than 60 beats per minute is considered a bradyarrhythmia. Some people normally have slow heart rates, especially people who are very physically fit. For them, a heartbeat slower than 60 beats per minute isn't dangerous and doesn't cause symptoms. But in other people, bradyarrhythmia can be due to a serious disease or other condition.
Bradyarrhythmias can be caused by:
- Heart attack
- Conditions that harm or change the heart's electrical activity, such as an underactive thyroid gland or aging
- An imbalance of chemicals or other substances, such as potassium, in the blood
- Some medicines, such as beta blockers
Bradyarrhythmias also can happen as a result of severe bundle branch block. Bundle branch block is a condition in which an electrical signal traveling down either or both of the bundle branches is delayed or blocked.
When this happens, the ventricles don't contract at exactly the same time, as they should. As a result, the heart has to work harder to pump blood to the body. The cause of bundle branch block often is an existing heart condition.
Arrhythmias in Children
A child's heart rate normally decreases as he or she gets older. A newborn's heart beats between 95 to 160 times a minute. A 1-year-old's heart beats between 90 to 150 times a minute, and a 6- to 8-year-old's heart beats between 60 to 110 times a minute.
A baby or child's heart can beat faster or slower than normal for many reasons. Like adults, when children are active, their hearts will beat faster. When they're sleeping, their hearts will beat slower. Their heart rates can speed up and slow down as they breathe in and out. All of these changes are normal.
Some children are born with heart defects that cause arrhythmias. In other children, arrhythmias can develop later in childhood. Doctors use the same tests to diagnose arrhythmias in children and adults.
Treatments for children who have arrhythmias include medicines, defibrillation (electric shock), surgically implanted devices that control the heartbeat, and other procedures that fix abnormal electrical signals in the heart.
What Causes an Arrhythmia?
An arrhythmia can occur if the electrical signals that control the heartbeat are delayed or blocked. This can happen if the special nerve cells that produce electrical signals don't work properly, or if electrical signals don't travel normally through the heart.
An arrhythmia also can occur if another part of the heart starts to produce electrical signals. This adds to the signals from the special nerve cells and disrupts the normal heartbeat.
Smoking, heavy alcohol use, use of certain drugs (such as cocaine or amphetamines), use of certain prescription or over-the-counter medicines, or too much caffeine or nicotine can lead to arrhythmias in some people.
Strong emotional stress or anger can make the heart work harder, raise blood pressure, and release stress hormones. In some people, these reactions can lead to arrhythmias.
A heart attack or an underlying condition that damages the heart's electrical system also can cause arrhythmias. Examples of such conditions include high blood pressure, coronary heart disease, heart failure, overactive or underactive thyroid gland (too much or too little thyroid hormone produced), and rheumatic heart disease.
In some arrhythmias, such as Wolff-Parkinson-White syndrome, the underlying heart defect that causes the arrhythmia is congenital (present at birth). Sometimes, the cause of an arrhythmia can't be found.
Who Is At Risk for an Arrhythmia?
Millions of Americans have arrhythmias. They're very common in older adults. About 2.2 million Americans have atrial fibrillation (a common type of arrhythmia that can cause problems).
Most serious arrhythmias affect people older than 60. This is because older adults are more likely to have heart disease and other health problems that can lead to arrhythmias.
Older adults also tend to be more sensitive to the side effects of medicines, some of which can cause arrhythmias. Some medicines used to treat arrhythmias can even cause arrhythmias as a side effect.
Some types of arrhythmia happen more often in children and young adults. Paroxysmal supraventricular tachycardias (PSVTs), including Wolff-Parkinson-White syndrome, are more common in young people. PSVT is a fast heart rate that begins and ends suddenly.
Major Risk Factors
Arrhythmias are more common in people who have diseases or conditions that weaken the heart, such as:
- Heart attack
- Heart failure or cardiomyopathy, which weakens the heart and changes the way electrical signals move around the heart
- Heart tissue that's too thick or stiff or that hasn't formed normally
- Leaking or narrowed heart valves, which make the heart work too hard and can lead to heart failure
- Congenital heart defects (problems that are present at birth) that affect the heart's structure or function
Other conditions also can increase the risk for arrhythmias, such as:
- High blood pressure
- Infections that damage the heart muscle or the sac around the heart
- Diabetes, which increases the risk of high blood pressure and coronary heart disease
- Sleep apnea (when breathing becomes shallow or stops during sleep), which can stress the heart because the heart doesn't get enough oxygen
- An overactive or underactive thyroid gland (too much or too little thyroid hormone in the body)
Also, several other risk factors can increase risk for arrhythmias. Examples include heart surgery, certain drugs (such as cocaine or amphetamines), or an imbalance of chemicals or other substances (such as potassium) in the bloodstream.
What Are the Signs and Symptoms of an Arrhythmia?
Many arrhythmias cause no signs or symptoms. When signs or symptoms are present, the most common ones are:
- Palpitations (feelings that your heart is skipping a beat, fluttering, or beating too hard or fast)
- A slow heartbeat
- An irregular heartbeat
- Feeling pauses between heartbeats
More serious signs and symptoms include:
- Weakness, dizziness, and lightheadedness
- Fainting or nearly fainting
- Shortness of breath
- Chest pain
How Are Arrhythmias Treated?
Common arrhythmia treatments include medicines, medical procedures, and surgery. Treatment is needed when an arrhythmia causes serious symptoms, such as dizziness, chest pain, or fainting.
Treatment also is needed if an arrhythmia increases your risk for complications, such as heart failure, stroke, or sudden cardiac arrest.
Medicines can be used to speed up a heart that’s beating too slow or slow down a heart that’s beating too fast. They also can be used to convert an abnormal heart rhythm to a normal, steady rhythm. Medicines that do this are called antiarrhythmics.
Some of the medicines used to slow a fast heart rate are beta blockers (such as metoprolol and atenolol), calcium channel blockers (such as diltiazem and verapamil), and digoxin (digitalis). These medicines often are used to slow the heart rate in people who have atrial fibrillation.
Some of the medicines used to restore an abnormal heartbeat to a normal rhythm are amiodarone, sotalol, flecainide, propafenone, dofetilide, ibutilide, quinidine, procainamide, and disopyramide. These medicines often have side effects. Some of the side effects can make an arrhythmia worse or even cause a different kind of arrhythmia.
People who have atrial fibrillation and some other arrhythmias often are treated with anticoagulants, or blood thinners, to reduce the risk of blood clots forming. Aspirin, warfarin (Coumadin®), and heparin are commonly used blood thinners.
Medicines also can control an underlying medical condition, such as heart disease or a thyroid condition, that might be causing an arrhythmia.
Some arrhythmias are treated with a pacemaker. A pacemaker is a small device that's placed under the skin of your chest or abdomen to help control abnormal heart rhythms.
This device uses electrical pulses to prompt the heart to beat at a normal rate. Most pacemakers contain a sensor that activates the device only when the heartbeat is abnormal.
Some arrhythmias are treated with a jolt of electricity delivered to the heart. This type of treatment is called cardioversion or defibrillation, depending on which type of arrhythmia is being treated.
Some people who are at risk for ventricular fibrillation are treated with a device called an implantable cardioverter defibrillator (ICD). Like a pacemaker, an ICD is a small device that’s placed under the skin in the chest. This device uses electrical pulses or shocks to help control life-threatening arrhythmias.
An ICD continuously monitors the heartbeat. If it senses a dangerous ventricular arrhythmia, it sends an electric shock to the heart to restore a normal heartbeat.
A procedure called catheter ablation is sometimes used to treat certain types of arrhythmia when medicines don’t work.
During this procedure, a long, thin, flexible tube is put into a blood vessel in your arm, groin (upper thigh), or neck. The tube is guided to your heart through the blood vessel. A special machine sends energy through the tube to your heart.
This energy finds and destroys small areas of heart tissue where abnormal heartbeats may cause an arrhythmia to start. Catheter ablation usually is done in a hospital as part of an electrophysiology study.
Sometimes, an arrhythmia is treated with surgery. This often occurs when surgery is already being done for another reason, such as repair of a heart valve.
One type of surgery for atrial fibrillation is called "maze" surgery. In this operation, the surgeon makes small cuts or burns in the atria that prevent the spread of disorganized electrical signals.
If coronary heart disease is causing arrhythmias, coronary artery bypass grafting may be recommended. This surgery improves blood supply to the heart muscle.
Vagal maneuvers are another arrhythmia treatment. These simple exercises sometimes can stop or slow down certain types of supraventricular arrhythmias. They do this by affecting the vagus nerve, which helps control the heart rate.
Some vagal maneuvers include:
- Holding your breath and bearing down (Valsalva maneuver)
- Immersing your face in ice-cold water
- Putting your fingers on your eyelids and pressing down gently
Vagal maneuvers aren't an appropriate treatment for everyone. Discuss with your doctor whether vagal maneuvers are an option for you.