An electrocardiogram, also called an ECG or EKG, analyses electrical currents that allow the heart to beat regularly. The electrical wave associated with each heartbeat is composed of different parts (PR or QT interval, QRS complex, etc.) that correspond to each stage of the beat: filling of the ventricles, contraction of the atria, contraction of the ventricles to eject blood into the aorta and pulmonary artery, and the opening and closing of the valves between each compartment. An ECG is used to measure the heart rate, detect potential arrhythmias (irregular heartbeats) and find causes that may explain chest pain (angina attacks) or other heart abnormalities such as a previous heart attack, an enlargement of the heart chambers (dilated cardiomyopathy) or an inflammation of the lining surrounding the heart (pericarditis). An ECG can be performed at rest or under stress (on a treadmill). It can be short in duration (recording for about 10 minutes) or spread out over one, two or sometimes even 14 days (dynamic Holter). The results of an electrocardiogram are interpreted by a cardiologist.
The most common ECG (i.e., at rest) is performed in a supine position. A dozen electrodes are attached to the skin, on the left and right wrists and ankles and on the rib cage. This method is painless and does not require the injection of any substance into the body. It is not necessary to fast.