The electrocardiogram (ECG) is a non-invasive test that detects and records the electrical activity of the heart.
The heart's rhythm and rate is controlled by series of electrical impulses. These impulses are generated by the heart's intrinsic pacemaker (the sinoatrial node). These electric impulses then travel across the heart muscle to cause contractions. It is these electrical impulses (or "waves") that the ECG records.
An ECG is ordered if the doctor suspects a problem with the heart's rate or rhythm. It is also ordered as a routine investigation before surgery or during follow-up after cardiac surgery.
By looking at the rhythm and measuring time intervals on the ECG, a doctor can determine if the electrical activity of the heart is normal, slow, fast or irregular. By measuring the amount of electrical voltage passing through different parts of the heart, a doctor may also be able to find out if a particular part of the heart is too large or is overworked.
The ECG is performed with the child lying down. The technician will then put several sensors (patches called "electrodes") on the chest, arms and legs. The electrodes are soft and do not cause any pain or discomfort. These electrodes are connected to wires called "leads", which are connected to the ECG machine (Figure 20.1). The electrical activity of the heart is then recorded on a moving strip of paper in the ECG machine. In an anxious child, the parent or a second technician may be needed to help provide reassurance. Occasionally, sedation might be ordered for a very anxious child. During the ECG recording, the child must lie quietly for about 30 seconds for accurate recording. Once the ECG is obtained (an example is shown in Figure 20.2), the doctor will interpret the recording.
Figure 20.1 The ECG machine and leads.
Figure 20.2 An example of an ECG recording.
No. There is no pain or risk associated with having an electrocardiogram. The machine records the electrical activity from the surface of the body; it does not send any electricity into the body.
No. ECG can be ordered as and when necessary by the doctor and no special preparation is required before doing the ECG.
