You can record a clinical 12-lead ECG using just 4 electrodes and an app on your iPad or iPhone. The automatic interpretation function allows for fast and easy documentation of your patients’ symptoms and disease patterns.
The entire process of depolarization and repolarization is depicted on the ECG. The individual events are represented as spikes and waves, each representing a specific part of the cardiac conduction cycle. This visual representation of the conduction system makes it possible to analyze the heart’s electrical activity.
The picture below shows the pathway of an electrical impulse as it corresponds to the spikes and waves on an ECG. To do this, the heart is shown on its side.
Figure 2: Pathway of an electrical impulse as it corresponds to the spikes & waves on an ECG (Source: Trappe, H-J/Schuster, H-P: EKG-Kurs für Isabel. Stuttgart, 6. Auflage (2013), S. 3 Abb 1.2)
The P wave represents the depolarization (contraction) of the atria, the PR segment the transmission of the electrical impulse to the ventricles, the QRS complex represents depolarization (contraction) of the ventricles and the T wave shows the repolarization (relaxation) of the ventricles. When disturbances of the conduction system are present, this can be detected via abnormalities of the spikes and waves on an ECG.
An electrocardiogram uses electrodes attached to the skin, which are able to detect electrical currents, in order to provide us with information about the heart. The information detected by the electrodes is used to calculate measurements, known as leads. A “lead” is an angle of looking at the heart. A standard ECG includes 12 leads, i.e. 12 different angles of orientation in regards to the heart. Each lead provides us with information about different parts of the heart. A standard ECG typically requires 10 electrodes in order to provide a 12-lead view.
Six Limb leads on the vertical/frontal plane: 3 Standard (I, II, III) and 3 Augmented (aVR, aVL, aVF)
Six Precordial leads on the horizontal plane: V1-V6
Supplementary leads: V7, V8, V9
An ECG provides us with information about the heart’s rhythm and rate, problems with the conduction system and/or its electrical axis. Circulation problems of the coronary arteries can also be detected, which can help to diagnose a heart attack.
Various cardiac disorders can be detected via ECG changes:
An ECG can be performed as a resting, exercise or long-term ECG.
During a resting ECG the body must be relaxed (at rest), as the neighboring muscles and nerves also produce electrical tension. The electrodes are attached to predetermined locations on the body, located on the chest, arms and legs, which are connected to the ECG machine via a cable. The electrodes can detect electrical tension of less than a millivolt, which is then transcribed onto graph paper to produce an ECG.
An exercise ECG (or stress ECG) is performed under physical stress, as some changes are only detected when the heart is strained. For example, a resting ECG is particularly unremarkable in the setting of Coronary Artery Disease (CAD).
Many heart rhythm disorders or ECG changes can be better detected and diagnosed via an exercise ECG. In addition, an exercise ECG is performed as part of the evaluation of chest pain in certain situations:
As with a resting ECG, the electrodes are attached to the skin and are connected to the ECG machine via a cable. The patient is placed on either a treadmill or a stationary bicycle. The level of resistance/speed is increased at regular intervals (usually every 2-3 minutes) until the patient can no longer exercise, the maximum heart rate is reached or symptoms and/or ECG changes indicating stress to the heart are present. The ECG reading, heart rate and blood pressure are continuously monitored during the test, and for a few minutes following, in order to observe the return of the heart rate to its baseline.
An exercise ECG should not be performed in the following situations, as it could cause cardiac injury:
An additional way to measure the activity of the heart is a long-term ECG. This measures the heart’s activity over 24 hours and can therefore detect many changes. The electrodes are attached to the skin and connected to a small mobile recording device via a cable. The gathered data is then interpreted by a physician.
A long-term ECG is often used in the following situations:
Long-term ECG’s are typically used to monitor heart rhythm or rate disturbances.