Tests & Procedures



EKG/ECG

The heart's electrical conduction system:

The heart is, in the 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 is regulated by an electrical conduction system that coordinates the contraction of the various chambers of the heart.

An electrical stimulus is generated by the sinus node (also called the sinoatrial node, or 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/her 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 travels from the sinus node to the atrioventricular node (also called AV node), where impulses are slowed down for a very short period, then continue down the conduction pathway via 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.

Normally at rest, as the electrical impulse moves through the heart, the heart contracts about 60 to 140 times a minute, depending on a person's age. Each contraction of the ventricles represents one heartbeat. The atria contract a fraction of a second before the ventricles so their blood empties into the ventricles before the ventricles contract.

What is an electrocardiogram (ECG)?

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

Why is an ECG performed?

The electrical activity of the heart is measured by an electrocardiogram. 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, or congestive heart failure.
  • Ischemia. A decreased blood flow to the heart muscle due to clogged or partially-clogged arteries.
  • 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 interfere with blood flow within the heart.
  • Chest trauma. Blunt trauma to the chest, such as that sustained 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 workup 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 medications
  • To check the heart's status after a heart-related procedure such as a cardiac catheterization, heart surgery, or electrophysiological studies

How does the doctor know what an ECG means?

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 short, flat segment is called the "PR interval." This represents the delay in the propagation of the electrical signal from the atria 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.
  • 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 the T wave. The T wave indicates the recovery period of the ventricles after contraction.

When the doctor studies your child's ECG, he or she 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 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 is the procedure for an ECG?

An ECG can be performed almost anywhere, as the equipment is very compact and portable. Thus, your child may undergo an ECG in a doctor's office, the ECG department of a 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 ten minutes, including attaching and detaching electrodes.

Obtaining an ECG typically includes the following steps:

  • Your child will lie flat on a table or bed for the procedure.
  • The ECG technician will need to have your child's chest uncovered in order to perform the test. Your child's privacy will be ensured by covering him or her with a sheet or gown and exposing only the necessary skin.
  • Electrodes (small, plastic patches) will be attached to your child's chest and one electrode will be attached to 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 your child's name and age into the machine's computer.
  • The ECG is started. It will be important for your 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 only a few 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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Online Resources of Cardiovascular Disorders

Last reviewed: 4/27/2013