Electrocardiogram (ECG)

What is an ECG? 

An ECG is one of the simplest and fastest procedures used to evaluate the heart. Electrodes (small, plastic patches) are placed at certain locations on the child’s chest, arms and legs. When the electrodes are connected to the ECG machine by lead wires, the electrical activity of the child’s heart is measured, interpreted and printed for the doctor’s information and further interpretation. 

What is an  exercise ECG ?
What is the
electrical activity of a heart?

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Why is an ECG performed? 

The electrical activity of the heart is measured by an ECG. 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 one, or more, of several heart-related conditions.

Some medical conditions which may cause changes in the ECG pattern include, but are not limited to, the following:

  • Conditions in which the heart is enlarged—these conditions can be caused by various factors, such as congenital (present at birth) heart defects, valve disorders, high blood pressure, congestive heart failure or conduction disturbances.
  • Ischemia—decreased blood flow to the heart muscle due to abnormal, clogged or partially-clogged coronary arteries which provide blood to the heart muscle.
  • Conduction disorders—a dysfunction in the heart’s electrical conduction system, which can make the heart beat too fast, too slow or at an uneven rate.
  • Electrolyte disturbances—an imbalance in the level of electrolytes, or chemicals, in the blood, such as potassium, magnesium or calcium.
  • Pericarditis—an inflammation or infection of the sac which surrounds the heart.
  • Valve disease—malfunction of one or more of the heart valves may cause an obstruction of the blood flow within the heart.
  • Chest trauma—blunt trauma to the chest, such as a motorist hitting the steering wheel in an automobile accident.
This list is presented as an example. It is not intended to be a comprehensive list of all conditions which may cause changes in the ECG pattern.

An ECG may also be performed for other reasons, including, but not limited to, the following:

  • During a physical examination to obtain a baseline tracing of the heart’s function (This baseline tracing may be used later as a comparison with future ECGs, to see if any changes have occurred.)
  • As part of a work-up prior to a procedure such as surgery to make sure no heart condition exists that might cause complications during or after the procedure
  • To check the function of an implanted pacemaker
  • To check the effectiveness of certain heart medicine
  • To check the heart’s status after a heart-related procedure such as a cardiac catheterization, heart surgery or electrophysiological studies
  • To check the effects of certain medicine on the heart rhythm

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What Does an ECG Mean? 

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

Illustration of a basic EKG tracing

Click image to enlarge.

  • 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 to pump blood to the ventricles.
  • The next part of the tracing is a short downward section connected to a tall upward section. This next part is called the "QRS complex." This part indicates that the ventricles (the two lower chambers of the heart) are electrically stimulated to pump out blood to the body.
  • The next short flat segment is called the "ST segment." The ST segment indicates the amount of time from the end of the contraction of the ventricles to the beginning of the "T wave".
  • The next upward curve is called the "T wave." The T wave indicates the recovery period of the ventricles.

When your child's physician studies the ECG, he 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 ECG is "looking" at a specific part of the heart from different angles. Variations in a lead may indicate a problem with the part of the heart associated with that particular lead.

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What is the procedure for an ECG? 

An ECG can be performed almost anywhere, as the equipment is very compact and portable. Because of this, a child may undergo an ECG in a doctor’s office, the ECG department of the hospital or clinic, in a procedure or testing area, in the emergency department, or even in the hospital room or bed. The equipment used includes the ECG machine, skin electrodes and lead wires which attach the electrodes to the ECG machine.

An ECG normally takes approximately five to 10 minutes, including attaching and detaching electrodes. During an ECG:

  • The child will usually lie flat on a table or bed for the procedure.
  • The ECG technician will need to have the child’s chest uncovered in order to perform the test. Privacy will be ensured by covering the child with a sheet or gown and exposing only the necessary skin.
  • Electrodes (small, plastic patches) will be attached to the child’s chest and one electrode will be attached on, or near, each arm and leg.
  • The lead wires will be attached to the skin electrodes.
  • Once the leads are attached, the technician may key in identifying information such as the child’s name and age into the machine’s computer.
  • The ECG is started. It will be important for the child to lie still and not talk during the procedure, so as not to interfere with the tracing. Parents can usually be present in the room and involved in reassuring and encouraging their child during the procedure. At this point, it will take about five more minutes (or less) for the tracing to be completed.
  • Once the tracing is completed, the technician will disconnect the leads and remove the skin electrodes.

Depending on the results of the ECG, additional tests or procedures may be scheduled to gather further diagnostic information.

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What is exercise ECG testing? 

An ECG is one of the simplest and fastest procedures used to evaluate the heart. Electrodes (small, plastic patches) are placed at certain locations on a child’s chest, arms and legs. When the electrodes are connected to the ECG machine by lead wires, the electrical activity of the child’s heart is measured, interpreted and printed for the doctor’s information and further interpretation.

An ECG tracing will be run at certain points during the test in order to compare the effects of increasing stress on the heart. On a treadmill, the incline and treadmill speed will be increased periodically in order to make the child exercise harder. If the child is riding a bicycle, he will pedal faster against increased resistance. The child will exercise until reaching a target heart rate (determined by the doctor based on the child’s age and physical status) or until the child is unable to continue due to fatigue, shortness of breath, chest pain, irregular heart rhythms or other symptoms.

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How is the exercise ECG test performed? 

The procedure is performed in a doctor’s office, clinic, hospital or medical center. The equipment used includes an ECG machine, electrodes (small, plastic patches that stick on the skin) and lead wires which attach to the skin electrodes. A blood pressure cuff attached to an electronic monitoring machine is used. A treadmill or stationary bicycle is used for exercise.

The child will have initial, or baseline, ECG and blood pressure readings done while sitting, and standing, prior to exercising. He will walk on the treadmill or pedal the bicycle during the exercise portion of the procedure. The incline of the treadmill will be gradually increased, or the resistance of the bicycle will be gradually increased, in order to give the child a more difficult workout. ECG and blood pressure will be monitored during the exercise portion of the test. The child will then sit after exercising while ECG and blood pressure are monitored for a short time, perhaps another 10 to 15 minutes.

The procedure will take about one hour, including check-in, preparation and the actual procedure.

After the procedure, a hospital stay is not necessary, unless your child’s doctor determines that the child’s condition requires further observation or hospital admission.

The child may feel a little tired or sore for a few hours after the procedure, particularly if he is not used to exercising. Otherwise, the child should feel normal within a few hours after the procedure, if not sooner.

Depending on the results of the exercise ECG, additional tests or procedures may be scheduled to gather further diagnostic information.

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How does the heart’s electrical conduction system work?

The heart is, in simplest terms, a pump made up of muscle tissue. Like all pumps, the heart requires a source of energy in order to function. The heart’s pumping action comes from a built-in, electrical, conduction system.

An electrical stimulus is generated by the sinus node (also called the sinoatrial (SA) node), which is a small area of specialized tissue located in the right atrium (right upper chamber) of the heart. Under normal conditions, the sinus node generates an electrical stimulus every time the heart beats (60 to 190 times per minute, depending on the age of the child and his activity level).

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 then travels from the sinus node to the atrioventricular (AV) node, where impulses are slowed down for a very short period, and continues down the conduction pathway via the bundle of His into the ventricles. The bundles of His divides into right and left pathways to provide electrical stimulation to both ventricles.

Normally, the electrical impulse moves through the heart’s conduction system, and the heart contracts. Each contraction of the ventricles represents one heart beat. The atria contract a fraction of a second before the ventricles so their blood empties into the ventricles before the ventricles contract.