An electrocardiogram, also called an ECG or EKG, is a simple, painless test that detects and records your heart’s electrical activity.

An EKG can show how fast your heart is beating, whether the rhythm of your heartbeats is steady or irregular, and the strength and timing of the electrical impulses passing through each part of your heart. You may have an EKG as part of a routine exam to screen for heart disease. This test also is used to detect and study heart problems such as heart attacks, arrhythmia or irregular heartbeat, and heart failure. Results from this test also may suggest other heart disorders.

An EKG may be recorded in a doctor’s office, an outpatient facility, in a hospital before major surgery, or as part of stress testing. For the test, you will lie still on a table. A nurse or technician will attach up to 12 electrodes to the skin on your chest, arms, and legs. Your skin may need to be shaved to help the electrodes stick. The electrodes are connected by wires to a machine that records your heart’s electrical activity on graph paper or on a computer. After the test, the electrodes will be removed.

An EKG has no serious risks. EKGs don’t give off electrical charges such as shocks. You may develop a slight rash where the electrodes were attached to your skin. This rash usually goes away on its own without treatment.

Doctors use a test called an EKG (electrocardiogram) to help diagnose heart block. This test detects and records the heart's electrical activity. An EKG records the strength and timing of electrical signals as they pass through the heart.

The data are recorded on a graph so your doctor can study your heart's electrical activity. Different parts of the graph show each step of an electrical signal's journey through the heart.

EKG

The image shows the standard setup for an EKG. In figure A, a normal heart rhythm recording shows the electrical pattern of a regular heartbeat. In figure B, a patient lies in a bed with EKG electrodes attached to his chest, upper arms, and legs. A nurse monitors the painless procedure.

Each electrical signal begins in a group of cells called the sinus node or sinoatrial (SA) node. The SA node is located in the right atrium (AY-tree-um), which is the upper right chamber of the heart. (Your heart has two upper chambers and two lower chambers.)

In a healthy adult heart at rest, the SA node sends an electrical signal to begin a new heartbeat 60 to 100 times a minute.

From the SA node, the signal travels through the right and left atria. This causes the atria to contract, which helps move blood into the heart's lower chambers, the ventricles (VEN-trih-kuls). The electrical signal moving through the atria is recorded as the P wave on the EKG.

The electrical signal passes between the atria and ventricles through a group of cells called the atrioventricular (AV) node. The signal slows down as it passes through the AV node. This slowing allows the ventricles enough time to finish filling with blood. On the EKG, this part of the process is the flat line between the end of the P wave and the beginning of the Q wave.

The electrical signal then leaves the AV node and travels along a pathway called the bundle of His. From there, the signal travels into the right and left bundle branches. The signal spreads quickly across your heart's ventricles, causing them to contract and pump blood to your lungs and the rest of your body. This process is recorded as the QRS waves on the EKG.

The ventricles then recover their normal electrical state (shown as the T wave on the EKG). The muscle stops contracting to allow the heart to refill with blood. This entire process continues over and over with each new heartbeat.

By careful placement of surface electrodes on the body, it is possible to record the complex, compound electrical signal of the heart. This tracing of the electrical signal is the electrocardiogram (ECG), also commonly abbreviated EKG (K coming kardiology, from the German term for cardiology). Careful analysis of the ECG reveals a detailed picture of both normal and abnormal heart function, and is an indispensable clinical diagnostic tool. The standard electrocardiograph (the instrument that generates an ECG) uses 3, 5, or 12 leads. The greater the number of leads an electrocardiograph uses, the more information the ECG provides. The term “lead” may be used to refer to the cable from the electrode to the electrical recorder, but it typically describes the voltage difference between two of the electrodes. The 12-lead electrocardiograph uses 10 electrodes placed in standard locations on the patient’s skin (image). In continuous ambulatory electrocardiographs, the patient wears a small, portable, battery-operated device known as a Holter monitor, or simply a Holter, that continuously monitors heart electrical activity, typically for a period of 24 hours during the patient’s normal routine.

A normal ECG tracing is presented in image. Each component, segment, and interval is labeled and corresponds to important electrical events, demonstrating the relationship between these events and contraction in the heart.

There are five prominent points on the ECG: the P wave, the QRS complex, and the T wave. The small P wave represents the depolarization of the atria. The atria begin contracting approximately 25 ms after the start of the P wave. The large QRS complex represents the depolarization of the ventricles, which requires a much stronger electrical signal because of the larger size of the ventricular cardiac muscle. The ventricles begin to contract as the QRS reaches the peak of the R wave. Lastly, the T wave represents the repolarization of the ventricles. The repolarization of the atria occurs during the QRS complex, which masks it on an ECG.

The major segments and intervals of an ECG tracing are indicated in image. Segments are defined as the regions between two waves. Intervals include one segment plus one or more waves. For example, the PR segment begins at the end of the P wave and ends at the beginning of the QRS complex. The PR interval starts at the beginning of the P wave and ends with the beginning of the QRS complex. The PR interval is more clinically relevant, as it measures the duration from the beginning of atrial depolarization (the P wave) to the initiation of the QRS complex. Since the Q wave may be difficult to view in some tracings, the measurement is often extended to the R that is more easily visible. Should there be a delay in passage of the impulse from the SA node to the AV node, it would be visible in the PR interval. image correlates events of heart contraction to the corresponding segments and intervals of an ECG.

An electrocardiogram also is called an EKG or ECG. Sometimes the test is called a 12-lead EKG or 12-lead ECG. This is because the heart's electrical activity most often is recorded from 12 different places on the body at the same time.

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.

An electrocardiogram (EKG) has no serious risks. It's a harmless, painless test that detects the heart's electrical activity. EKGs don't give off electrical charges, such as shocks.

You may develop a mild rash where the electrodes (soft patches) were attached. This rash often goes away without treatment.

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 To Expect During an Electrocardiogram

An electrocardiogram (EKG) is painless and harmless. A nurse or technician will attach soft, sticky patches called electrodes to the skin of your chest, arms, and legs. The patches are about the size of a quarter.

Often, 12 patches are attached to your body. This helps detect your heart's electrical activity from many areas at the same time. The nurse may have to shave areas of your skin to help the patches stick.

After the patches are placed on your skin, you'll lie still on a table while the patches detect your heart's electrical signals. A machine will record these signals on graph paper or display them on a screen.

The entire test will take about 10 minutes.

EKG

The picture shows the standard setup for an EKG. In figure A, a heart rhythm recording shows the electrical pattern of a normal heartbeat. In figure B, a patient lies in a bed with EKG electrodes attached to his chest, upper arms, and legs. A nurse oversees the painless procedure.

The image shows the standard setup for an EKG. In figure A, a normal heart rhythm recording shows the electrical pattern of a regular heartbeat. In figure B, a patient lies in a bed with EKG electrodes attached to his chest, upper arms, and legs. A nurse monitors the painless procedure.

Special Types of Electrocardiogram

The standard EKG described above, called a resting 12-lead EKG, only records seconds of heart activity at a time. It will show a heart problem only if the problem occurs during the test.

Many heart problems are present all the time, and a resting 12-lead EKG will detect them. But some heart problems, like those related to an irregular heartbeat, can come and go. They may occur only for a few minutes a day or only while you exercise.

Doctors use special EKGs, such as stress tests and Holter and event monitors, to help diagnose these kinds of problems.

Stress Test

Some heart problems are easier to diagnose when your heart is working hard and beating fast. During stress testing, you exercise to make your heart work hard and beat fast while an EKG is done. If you can't exercise, you'll be given medicine to make your heart work hard and beat fast.

For more information, go to the Health Topics Stress Testing article.

Holter and Event Monitors

Holter and event monitors are small, portable devices. They record your heart's electrical activity while you do your normal daily activities. A Holter monitor records your heart's electrical activity for a full 24- or 48-hour period.

An event monitor records your heart's electrical activity only at certain times while you're wearing it. For many event monitors, you push a button to start the monitor when you feel symptoms. Other event monitors start automatically when they sense abnormal heart rhythms.

What To Expect After an Electrocardiogram

After an electrocardiogram (EKG), the nurse or technician will remove the electrodes (soft patches) from your skin. You may develop a rash or redness where the EKG patches were attached. This mild rash often goes away without treatment.

You usually can go back to your normal daily routine after an EKG.

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.