SElectrocardiography (ECG or EKG: kardia, meaning heart) is the recording of the electrical activity of the heart. Traditionally this is in the form of a transthoracic (across the thorax or chest) interpretation of the electrical activity of the heart over a period of time, as detected by electrodes attached to the surface of the skin and recorded or displayed by a device external to the body. The recording produced by this noninvasive procedure is termed an electrocardiogram (also ECG or EKG). It is possible to record ECGs invasively using an implantable loop recorder.
An ECG is used to measure the heart’s electrical conduction system. It picks up electrical impulses generated by the polarization and depolarization of cardiac tissue and translates into a waveform. The waveform is then used to measure the rate and regularity of heartbeats, as well as the size and position of the chambers, the presence of any damage to the heart, and the effects of drugs or devices used to regulate the heart, such as a pacemaker.
Most ECGs are performed for diagnostic or research purposes on human hearts, but may also be performed on animals, usually for diagnosis of heart abnormalities or research.
Twelve-lead ECG of a 26-year-old male with an incomplete RBBB
General symptoms indicating use of electrocardiography include:
Symptoms of myocardial infarction
Symptoms of pulmonary embolism
Syncope or collapse
It is also used to assess patients with systemic disease, as well as monitoring during anesthesia and critically ill patients.
Screening for coronary heart disease
The U.S. Preventative Services Task Force do not recommend either the ECG or any other cardiac imaging procedure as a routine screening procedure in patients without symptoms and those at low risk for coronary heart disease. This is because overuse of the procedure is more likely to supply incorrect supporting evidence for a nonexistent problem than to detect a true problem. Tests that falsely indicate the existence of a problem are likely to lead to misdiagnosis, the recommendation of invasive procedures, or overtreatment, and the risks associated with managing false information are usually more troublesome than not using ECG results to make a health recommendation in low-risk individuals.
Persons employed in certain critical occupations, such as aircraft pilots, or in certain environments, such as high altitudes, may be required to have an ECG as part of a regulatory regime.
Characteristic changes seen on electrocardiography in myocardial infarction is included in the WHO criteria as revised in 2000. According to these, a cardiac troponin rise accompanied by either typical symptoms, pathological Q waves, ST elevation or depression or coronary intervention are diagnostic of myocardial infarction.
Electrocardiogram of a patient with pulmonary embolism showing sinus tachycardia of approximately 150 beats per minute and right bundle branch block.
In pulmonary embolism, an ECG may show signs of right heart strain or acute cor pulmonale in cases of large PEs—the classic signs are a large S wave in lead I, a large Q wave in lead III and an inverted T wave in lead III (S1Q3T3). This is occasionally (up to 20%) present, but may also occur in other acute lung conditions and has, therefore, limited diagnostic value. This S1Q3T3 pattern from acute right heart strain is termed the "McGinn-White sign" after the initial describers. The most commonly seen signs in the ECG is sinus tachycardia, right axis deviation, and right bundle branch block. Sinus tachycardia was however still only found in 8–69% of people with PE.