EcgEdit
An electrocardiogram (ECG), traditionally written as ECG or EKG in older texts, is a noninvasive test that captures the heart’s electrical activity. By placing a handful of small electrodes on the chest and limbs, a machine records the timing and pattern of electrical impulses as the heart cycles through its beats. The resulting traces help clinicians diagnose a wide range of cardiac conditions, from fast or slow rhythms to events indicating ischemia or prior myocardial injury. In modern practice, ECGs are routine in emergency care, outpatient clinics, anesthesia, and preventive medicine, and they are increasingly integrated with digital health ecosystems through telemedicine and automated interpretation tools electrocardiography.
The basic idea of electrocardiography traces back to early 20th-century work by Willem Einthoven, whose development of the practical electrocardiograph and the concept of the limb leads laid the groundwork for what would become a standard clinical test. The classic framework uses a set of standard limb leads (I, II, III) and augmented limb leads (aVR, aVL, aVF) together with precordial (chest) leads (V1–V6) to provide a comprehensive view of the heart’s electrical activity from multiple angles. This framework is sometimes referred to as a 12-lead ECG, and it remains at the core of diagnostic practice despite rapid advances in portable and digital technologies Willem Einthoven Einthoven's triangle.
History
The ECG emerged from early attempts to visualize the heart’s electrical signals. Einthoben’s work in the early 1900s introduced a practical device and the three-lead system that would evolve into the universally used 12-lead configuration. Over the decades, refinements in electrode technology, signal processing, and standardization of lead placement improved reliability, reproducibility, and the ability to identify subtle abnormalities. Today, ECGs are analyzed by clinicians and supported by computer-assisted algorithms, with data often stored in electronic health records and shared across care settings electrocardiography.
Technology and methods
12-lead ECG
A standard 12-lead ECG records electrical activity from multiple viewpoints on the body, producing a composite view of rhythm, conduction, and repolarization. Key waveform components include the P wave (atrial depolarization), the PR interval, the QRS complex (ventricular depolarization), the ST segment, and the T wave (ventricular repolarization). Intervals and amplitudes are measured to detect abnormalities such as atrioventricular block, bundle-branch block, myocardial ischemia, and electrolyte disturbances. The 12-lead setup is widely regarded as the gold standard for diagnostic accuracy in many clinical settings and remains the reference against which many consumer devices are measured QT interval QRS complex ST segment.
Ambulatory ECG and wearables
Beyond a single resting recording, clinicians use ambulatory ECG monitoring to assess intermittent symptoms or occult rhythm disturbances. Holter monitors provide continuous recording over 24–72 hours, while event recorders or loop recorders can prolong monitoring for weeks or months, capturing infrequent episodes. In recent years, wearable technologies and smartphone-linked ECG devices have proliferated, enabling patient-initiated or automated analysis in real time. These consumer and professional devices bring convenience and early detection opportunities, but they also raise questions about data quality, interpretation standards, and the appropriate clinical response to incidental findings. In medical practice, interpretations from wearables are integrated with clinician oversight and sometimes remote telemetry Holter monitor Ambulatory electrocardiography Wearable technology.
Clinical relevance
Indications
ECG testing is indicated in a variety of clinical scenarios, including evaluation of palpitations, syncope, chest pain, suspected arrhythmias, preoperative risk assessment, and post-infarction monitoring. In acute care, ECG changes can identify acute myocardial infarction, ischemia, or electrolyte derangements that require urgent management; in chronic care, ECGs help track known conduction disease or cardiomyopathy and guide therapy decisions such as antiarrhythmic drugs or pacing. Important related topics include arrhythmias (e.g., atrial fibrillation, ventricular tachycardia) and myocardial infarction risk assessment, which are described in depth in related articles Arrhythmia Myocardial infarction.
Interpretation
Interpreting ECGs requires integration of waveform characteristics with clinical context. Board-certified readers assess rhythm regularity, rate, axis, PR interval, QRS duration, QT interval, ST-segment deviations, and T-wave morphology. Variability in interpretation can occur, especially with borderline findings or artifacts, which underscores the value of established criteria and, increasingly, decision support from validated algorithms. While automated readings can flag potential abnormalities, expert review remains essential to avoid misclassification or overdiagnosis. The core interpretive concepts connect to broader topics in cardiac physiology and diagnostic testing RS interval QRS complex ST segment.
Safety and limitations
ECG testing is noninvasive and low-risk, but it is not infallible. Artifacts from movement, poor electrode contact, or external electrical interference can obscure signals. The ECG provides electrical information about the heart but not direct imaging of anatomy; imaging studies, echocardiography, and other tests often complement ECG findings to establish a diagnosis. Cost, access, and the risk of incidental findings are ongoing considerations in policy debates about broader use of ECG testing in populations outside of traditional high-risk groups. These issues feature prominently in discussions surrounding sports screening, preventive care, and the allocation of health care resources Echocardiography.
Controversies and policy debates
The use of ECGs in certain settings, especially as part of screening programs for athletes or asymptomatic individuals, generates debate. Proponents argue that ECG-based screening can detect risk factors for sudden cardiac death and enable preventive action. Critics contend that routine screening in low-risk populations increases false positives, leads to unnecessary testing and anxiety, and consumes resources better allocated elsewhere. Guidelines across countries and professional societies reflect differing risk-benefit assessments, and decisions often hinge on population-specific prevalence, test performance, and cost-effectiveness. From a pragmatic perspective, the most defensible approach emphasizes evidence-based use, targeted screening for high-risk groups, and robust follow-up protocols to avoid routine overdiagnosis. Critics who frame these issues as primarily about broader social justice concerns may overlook the practical benefits of focusing resources on high-yield testing, while proponents emphasize patient safety and timely treatment. In the wider health policy landscape, the balance between innovation, regulation, and value-based care continues to shape how ECG testing is deployed and reimbursed Athletic heart syndrome Wearable technology Health technology assessment.