Electrocardiogram (ECG)

Measurement of the heart’s electrical activity

An ECG is a routine examination of the electrical activity of the heart that can be undertaken in hospitals or in physicians’ practices. It is a fairly quick, non-invasive and completely painless examination.

The regular movements of the heart chambers are controlled by a complex system of electrical impulses that cause the upper chambers (atria) and the lower chambers (ventricles) to contract and relax rhythmically and consistently. If these electrical impulses are interrupted, delayed or sent down the wrong path, arrhythmia arises with specific symptoms such as irregular heart beat, shortness of breath (dyspnoea) or loss of consciousness (syncope). Furthermore the electrical signals can show signs of structural or metabolic changes like enlargement or hypoxia of the cardiac muscle.

During the examination, electrode pads are attached to the arms, legs and to specific locations on the patient’s chest. These pads record the electricity originating from the heart. The voltage is graphically depicted by a set of wave lines on a moving strip of paper or on the doctor’s monitor. The results are available directly and can be saved to be compared with earlier or later findings. The patient has to lie down face up to avoid contractions of the voluntary muscles in the rest of the body since these electrical signals obscure the cardiac ones.

During the ECG, the size, timing and character of the electrical impulses moving through the patient’s heart are recorded. Thus, the examining doctor is able to define the heart rate and rhythm and to find out, for example, whether the heart beat is abnormally slow or fast. Additionally, the recordings provide important information about the possibility of impaired blood flow to the heart muscle, enlargement (hypertrophy) of the heart and damage to the heart muscle, for example due to a previous or acute heart attack.

On the basis of a detailed assessment of these findings, the conditions listed below can be diagnosed.

  • Different rhythm disturbances (arrhythmias) that can be due to several reasons, including abnormally fast (tachycardia) or abnormally slow (bradycardia) heart rhythms as well as premature beats and atrial fibrillation, a disorder in which the upper heart chambers alone beat so fast that they no longer contract properly.
  • Some congenital heart diseases such as Wolf-Parkinson-White syndrome or long QT syndrome.
  • Cardiac hypertrophy (thickened heart muscle).
  • Cardiac dilatation (enlarged cardiac chambers).
  • Cardiomyopathy—a range of conditions in which the heart muscle (myocardium) does not function normally because of several reasons, including several congenital forms of cardiomyopathies.
  • Previous or acute heart attack.
  • Inflammation of the heart (myocarditis) or its lining (pericarditis).

Value and limitations of ECG

The ECG is an easy and helpful test for assessment of the heart’s function and possible underlying problems. However, it does have limitations. The results of an ECG examination are often unspecific, meaning that abnormal findings do not refer to one condition but could be the result of different problems. Furthermore, a normal ECG does not rule out heart disease. Therefore, additional tests are recommended, especially when the ECG confirms the suspicion of a congenital heart defect.

These further tests could include imaging procedures such as echocardiography, magnetic resonance imaging (MRI), computed tomography (CT) or, if necessary, invasive procedures such as cardiac catheterisation. These methods can be used in conjunction with the ECG, so that different phases of the heart beat can be assigned to the images of the heart.

Specific ECG examinations: Holter ECG and stress ECG

For some conditions, rhythm disturbances or associated problems only occur occasionally or under specific circumstances (for example at night, when the patient is asleep or during exercise), which means that they might not be detected during the fairly short ECG examination. Therefore, two types of specific tests can be undertaken that are more likely to detect such problems.

One of these tests is the Holter ECG (sometimes also referred to as long-time ECG or as ambulatory ECG). This test monitors the heart’s electrical activity for an extended period of time. Between three and eight electrode pads are attached to the patient’s upper body and connected to a small portable device that the patient is able carry about during the recording. This test usually takes 24 hours, but it can also take up to several days, depending on the individual case and the problem being assessed.

During the time of recording, the patient is asked to keep an event diary in which he or she writes down the time and type of activities that they are doing, as well as the symptoms that they experience. Thus, the physician can compare the ECG findings to the patient’s notes and assign occurred symptoms and arrhythmias to specific activities.

If some symptoms only occur under strenuous conditions, these can be detected and assessed with a stress ECG. During this test, the patient is asked to exercise while the electrical activity of the heart is monitored. In this way, the doctor can establish whether there are any limitations to the heart’s function or the patient’s exercise tolerance. If a patient is unable to exercise, or concomitant investigations like echocardiography or MRI are to be done simultaneously, specific drugs stimulating the heart beat can be given instead to simulate a strenuous activity.

Author(s): Eva Niggemeyer
Reviewed by: Dr. Alfred Hager
Last updated: 2008-09-23