Electrocardiogram
An electrocardiogram (ECG) is one of the simplest and fastest procedures used to evaluate the heart. This test is particularly useful to diagnose a problem called an arrhythmia, which is an irregular heartbeat. The electrical information that is recorded provides a graphic representation of the heart’s function.
The data is recorded to a paper printout, sometimes called a tracing.Each lead of the ECG looks at a specific part of the heart from different angles. When your child's doctor studies the tracing of the ECG, they look at the size, shape and length of the waveforms and how fast or slow the heart is beating. If the variations differ from a normal pattern, the physician may suspect the presence of a heart problem.
Why is an ECG performed?
Some medical conditions that may cause changes in the ECG pattern include, but are not limited to, the following:
- Enlarged heart - this condition can be caused by various factors, such as congenital heart defects, valve disorders, high blood pressure, congestive heart failure or conduction disturbances.
- Ischemia - decreased blood flow to the heart muscle due to clogged, partially clogged, or abnormal arteries.
- Conduction disorders - a dysfunction in the heart's electrical conduction system that 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 that surrounds the heart.
- Valve disease - malfunction of one or more of the heart valves may cause an obstruction or leaking 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.
An ECG may also be performed for other reasons. It may be used 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.
How does the physician know what an ECG means?
Almost everyone has seen a basic ECG tracing. However, what does it mean? 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 (two lower chambers of the heart). The next part of the tracing is a short downward section connected to a tall upward section. This is called the "QRS complex." This part indicates that the ventricles 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.
When your child's physician studies an ECG, they look at the size, shape and length of each part of the ECG as well as how fast or slow the heart is beating. The tracing for each lead of a 12-lead ECG will look different, but will have the same basic components as described above.
How is an ECG performed?
An ECG can be performed almost anywhere, as the equipment is very compact and portable. Thus, your child may undergo an ECG in a physician'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 to complete, including attaching and detaching electrodes. During an ECG 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 them with a sheet or gown and exposing only the necessary skin. Electrodes 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 will key in identifying information such as your child's name and age into the machine's computer. It is important that your child lie still and not talk during the procedure, so as not to interfere with the tracing. Parents can be present in the room and involved in reassuring and encouraging their child during the procedure.
At this point, it will take approximately one more minute for the tracing to be completed. Once the tracing is completed, the technician will disconnect the leads and remove the skin electrodes.
Signal-average ECG
This test is done in the same manner as a resting ECG, except that the heart's electrical activity is recorded over a longer period, usually 5-10 minutes. Signal-average ECG is done when an arrhythmia is suspected but not seen on a resting ECG. Signal-average ECG has increased sensitivity to abnormal heart activity called "late potentials."