What is an electrocardiogram?

An EKG (also called ECG) 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 EKG/ECG machine by lead wires, the electrical activity of your child's heart is measured, interpreted, and printed out for the physician's information and further interpretation.

Why is an EKG 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 EKG from the normal tracing can indicate one, or more, of several heart-related conditions.

Some medical conditions which may cause changes in the EKG 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 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 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

(NOTE: 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 EKG pattern.)

An EKG 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 EKGs, 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 medications
  • To check the heart's status after a heart-related procedure such as a cardiac catheterization, heart surgery, or electrophysiological studies

Understanding EKG tracings :

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

EKG tracings used in electrocardiogram available in diagnostics at the Herma Heart Institute at Children's Wisconsin

  • The first little upward notch of the EKG tracing is called the "P wave." The P wave indicates that the atria (the two upper chambers of the heart) are contracting to pump out blood.
  • 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 contracting to pump out blood to the body.
  • The next short upward 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 rest period before the ventricles begin to contract for the next beat.
  • The next upward curve is called the "T wave." The T wave indicates the resting period of the ventricles.

When your child's physician studies your child's EKG, he/she looks at the size and length of each part of the EKG. Variations in size and length of the different parts of the tracing may be significant.

The tracing for each lead of a 12-lead EKG will look different, but will have the same basic components as described above. Each lead of the 12-lead EKG 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.

What is the procedure for an EKG?

An EKG can be performed almost anywhere, as the equipment is very compact and portable. Thus, your child may undergo an EKG in a physician's office, the EKG 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 EKG machine, skin electrodes, and lead wires which attach the electrodes to the EKG machine.

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

  • Your child will lie flat on a table or bed for the procedure.
  • The EKG 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/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 EKG 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 approximately 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 EKG, additional tests or procedures may be scheduled to gather further diagnostic information.

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 energy comes from a built-in, electrical, conduction system.

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 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 it stops for a very short period, and continues down the conduction pathways via the bundle of His into the ventricles. The bundle 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 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.

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