electrocardiography

electrocardiography
Name	Electrocardiography
Caption	A 12-lead ECG tracing
Synonyms	ECG, EKG
ICD9	89.52
MedlinePlus	003868
LOINC	11524-6, 11525-3, 29275-3

electrocardiography is a fundamental diagnostic tool in cardiology that records the electrical activity of the heart over a period of time using electrodes placed on the skin. These recordings, known as electrocardiograms, are essential for detecting and diagnosing a wide range of cardiac conditions, from myocardial infarction to arrhythmia. The non-invasive procedure is routinely performed in settings ranging from general practitioner offices to emergency departments and cardiac catheterization labs. Its development, pioneered by figures like Willem Einthoven, revolutionized the understanding and clinical management of heart disease.

History

The foundational principles were established in the late 19th century with the work of Augustus Waller, who recorded the first human electrocardiogram using a capillary electrometer. The field was revolutionized by Willem Einthoven, who invented the string galvanometer in the early 20th century, for which he received the Nobel Prize in Physiology or Medicine in 1924. Subsequent advancements included the development of the 12-lead ECG by Frank Norman Wilson and the introduction of ambulatory monitoring devices like the Holter monitor pioneered by Norman J. Holter. The integration of digital technology and computerized analysis in the late 20th century, supported by institutions like the American Heart Association, has further refined its diagnostic capabilities.

Medical uses

It is a cornerstone for diagnosing acute conditions such as ST-elevation myocardial infarction and identifying life-threatening arrhythmias like ventricular fibrillation. It is routinely used to evaluate symptoms like chest pain, palpitations, and syncope, and is a standard component of preoperative assessment before major surgeries. The test is also critical for monitoring patients with known heart disease, assessing the effects of medications like digoxin, and screening for conditions in specific populations, such as athletes in programs like those overseen by the International Olympic Committee. Furthermore, it is indispensable in guiding procedures within the catheterization laboratory and for the management of implanted devices like those from Medtronic.

Physiology

The electrical impulse originates in the sinoatrial node, often called the heart's natural pacemaker, located in the right atrium. This impulse then spreads through the atria, causing atrial contraction, before being delayed at the atrioventricular node to allow for ventricular filling. The signal then travels rapidly down the bundle of His and its branches, the right bundle branch and left bundle branch, ultimately activating the ventricles via the Purkinje fibers. This coordinated sequence produces characteristic waveforms: the P wave represents atrial depolarization, the QRS complex signifies ventricular depolarization, and the T wave corresponds to ventricular repolarization.

ECG leads and placement

The standard configuration consists of 12 leads that provide different electrical perspectives of the heart. These include six limb leads (I, II, III, aVR, aVL, aVF) and six precordial leads (V1 through V6). Proper electrode placement is critical; limb electrodes are typically placed on the wrists and ankles, while the precordial electrodes are positioned across the chest in specific anatomical locations relative to structures like the sternum and midclavicular line. Specialized placements, such as a right-sided ECG or posterior leads, may be used to evaluate specific conditions like right ventricular infarction. The system was standardized through the work of the American Heart Association and the Heart Rhythm Society.

Interpretation

Systematic analysis involves assessing the heart rate, cardiac rhythm, electrical axis, and intervals such as the PR interval, QRS duration, and QT interval. Key diagnostic patterns include ST segment elevation indicative of acute coronary syndrome, Q waves suggesting prior myocardial infarction, and various morphologies associated with bundle branch block. Arrhythmias are identified by their characteristic signatures, such as the sawtooth pattern of atrial flutter or the absence of P waves in atrial fibrillation. Algorithms from organizations like the European Society of Cardiology aid in standardized diagnosis, particularly for conditions like Brugada syndrome.

Technical details

Modern machines are digital systems that amplify, filter, and digitize the small electrical signals detected by the electrodes. Key specifications include a standard recording speed of 25 mm/s, a calibration of 10 mm/mV, and bandpass filtering to reduce artifacts from sources like skeletal muscle or alternating current. The output can be displayed in real-time on a monitor, printed on specialized graph paper, or stored electronically in systems like Picture Archiving and Communication System. Innovations continue with developments in wearable technology from companies like Apple Inc. and advanced signal processing techniques researched at institutions like the Massachusetts Institute of Technology.

Category:Cardiology Category:Medical tests Category:Electrophysiology