Electrocardiogram EKG In-Depth

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What is an electrocardiogram (EKG / ECG)?

An EKG (also called ECG) is one of the simplest and fastest procedures used to evaluate the heart. Before the test, electrodes (small, plastic patches) are placed at certain locations on your child's chest, arms and legs. After 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 to examine.

Why is an electrocardiogram (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), we can make a graphic representation, or tracing, of the electrical activity. Changes in an EKG can indicate that your child has a heart-related condition.

Some medical conditions which may cause changes in the EKG pattern include:

  • conditions in which the heart is enlarged- 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
  • left ventricular hypertrophy- (enlargement of the left ventricle) High blood pressure makes the heart work harder causing the muscle of the left ventricle to enlarge. The echo can detect problems with the heart such as enlargement, abnormalities in motion of the heart wall, blood clots, and heart valve abnormalities. It also gives a good measurement of the strength of the heart muscle (ejection fraction)
  • 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, a condition called arrhythmia or disrhythmia
  • 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 hitting the steering wheel in an automobile accident.

NOTE: This list just contains examples. It’s not intended to be a comprehensive list of all conditions that may cause changes in the EKG pattern.)

An EKG may also be performed for other reasons, including: 

  • during a physical exam to obtain a baseline tracing of the heart's function
  • 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

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 your child’s age of 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.

Understanding EKG tracings

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

  • 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 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 contracting to pump out blood to the body (depolarization).
  • 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 doctor studies your child's EKG, 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?

A resting EKG normally takes 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. As a parent, you can probably be in the room and involved in reassuring and encouraging your child during the procedure.
  • Once the tracing is completed, the technician will disconnect the leads and remove the skin electrodes.

There are several variations of the EKG test, including:

  • Exercise EKG, or stress test- Your child is attached to the EKG machine as described above. Rather than lying down, your child exercises by walking on a treadmill or pedaling a stationary bicycle while the EKG is recorded. This test is done to assess changes in the EKG during stress such an exercise.
  • Signal-average EKG- This procedure is done in the same manner as a resting EKG, except that the heart's electrical activity is recorded over a longer period of time, usually 15 to 20 minutes. Signal-average EKG is done when arrhythmia is suspected but not seen on a resting EKG.
  • Holter monitor- This EKG recording is done over a period of 24 or more hours. Three electrodes are attached to your child's chest and connected to a small, portable EKG recorder by lead wires. Your child goes about his usual daily activities (except for activities such as taking a shower, swimming or any activity causing an excessive amount of sweating) during this procedure. There are two types of Holter monitoring:
    • continuous recording — an EKG recorded continuously during the entire testing period
    • event monitor, or loop recording—an EKG recorded only when your child starts the recording when symptoms are felt

Holter monitoring may be done when a problem is suspected but not seen on a resting or signal-average EKG.

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

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