Electrocardiogram
An electrocardiogram (ECG) is a simple diagnostic technique that measures the electrical activity inside the heart, and is fundamental to cardiac diagnosis. Many different conditions - not just acute heart attack - become apparent through characteristic ECG changes, including chronically reduced blood flow to the heart (myocardial ischemia) and cardiac arrhythmias, which can be detected using a resting ECG, ambulatory ECG or exercise ECG.
What is an electrocardiogram?
An electrocardiogram, or ECG, detects and records the electrical activity of the heart. Every heartbeat is a contraction of the heart muscle that is triggered by an electrical signal or impulse. This impulse normally originates in the sinus node, a specific area located inside the right atrium, from where it is transmitted along a special conduction pathway to the entire myocardium (heart muscle), causing the heart to contract.
Using electrodes that measure the activity of heart muscle cells by recording changes in their voltage over time, an ECG can not only measure heart rate and heart rhythm, but also provide information on the activity of the atria and ventricles. Although this allows physicians to detect abnormalities such as cardiac arrhythmias and heart attacks, additional diagnostic tests will be required in order to establish an accurate diagnosis.
Resting ECG
A standard (or resting) ECG only takes a short time to complete and is performed with the patient lying down. A number of small metal patches (electrodes) are placed onto the patient's arms, legs and chest, which allow changes in voltage to be recorded by the ECG device. The result is a characteristic heart trace that corresponds to the activity of the patient's heart.
Exercise ECG
An exercise ECG records the activity of the heart while the patient is exercising at a predefined level of intensity, either on a stationary bike or on a treadmill. The patient's blood pressure and heart rate are monitored, while the ECG trace can provide evidence as to whether exercising leads to cardiac arrhythmia.
Ambulatory ECG
In order to be able to obtain an ambulatory ECG, the patient has to be fitted with a portable ECG recorder. This can be set to record the heart's activity for between one to three days, and can be used to record intermittent symptoms such as cardiac arrhythmias or ectopic beats (extrasystoles) that only occur from time to time. This test often involves fewer electrodes than a standard ECG or an exercise ECG.
