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Electrocardiography

Electrocardiography is the process of producing an electrocardiogram (ECG or EKG[a]), a recording of the heart's electrical activity through repeated cardiac cycles.[4] It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the heart[5] using electrodes placed on the skin. These electrodes detect the small electrical changes that are a consequence of cardiac muscle depolarization followed by repolarization during each cardiac cycle (heartbeat). Changes in the normal ECG pattern occur in numerous cardiac abnormalities, including:

"ECG" and "EKG" redirect here. For other uses, see ECG (disambiguation) and EKG (disambiguation).

Electrocardiography

Traditionally, "ECG" usually means a 12-lead ECG taken while lying down as discussed below. However, other devices can record the electrical activity of the heart such as a Holter monitor but also some models of smartwatch are capable of recording an ECG. ECG signals can be recorded in other contexts with other devices.


In a conventional 12-lead ECG, ten electrodes are placed on the patient's limbs and on the surface of the chest. The overall magnitude of the heart's electrical potential is then measured from twelve different angles ("leads") and is recorded over a period of time (usually ten seconds). In this way, the overall magnitude and direction of the heart's electrical depolarization is captured at each moment throughout the cardiac cycle.[11]


There are three main components to an ECG:[12]


During each heartbeat, a healthy heart has an orderly progression of depolarization that starts with pacemaker cells in the sinoatrial node, spreads throughout the atrium, and passes through the atrioventricular node down into the bundle of His and into the Purkinje fibers, spreading down and to the left throughout the ventricles.[12] This orderly pattern of depolarization gives rise to the characteristic ECG tracing. To the trained clinician, an ECG conveys a large amount of information about the structure of the heart and the function of its electrical conduction system.[13] Among other things, an ECG can be used to measure the rate and rhythm of heartbeats, the size and position of the heart chambers, the presence of any damage to the heart's muscle cells or conduction system, the effects of heart drugs, and the function of implanted pacemakers.[14]

Chest pain or suspected (heart attack), such as ST elevated myocardial infarction (STEMI)[15] or non-ST elevated myocardial infarction (NSTEMI)[16]

myocardial infarction

Symptoms such as , murmurs,[17] fainting, seizures, funny turns, or arrhythmias including new onset palpitations or monitoring of known cardiac arrhythmias

shortness of breath

Medication monitoring (e.g., , Digoxin toxicity) and management of overdose (e.g., tricyclic overdose)

drug-induced QT prolongation

such as hyperkalemia

Electrolyte abnormalities

monitoring in which any form of anesthesia is involved (e.g., monitored anesthesia care, general anesthesia). This includes preoperative assessment and intraoperative and postoperative monitoring.

Perioperative

Cardiac stress testing

(CTA) and magnetic resonance angiography (MRA) of the heart (ECG is used to "gate" the scanning so that the anatomical position of the heart is steady)

Computed tomography angiography

in which a catheter is inserted through the femoral vein and can have several electrodes along its length to record the direction of electrical activity from within the heart.

Clinical cardiac electrophysiology

protection: any ECG used in healthcare may be attached to a person who requires defibrillation and the ECG needs to protect itself from this source of energy.

Defibrillation

is similar to defibrillation discharge and requires voltage protection up to 18,000 volts.

Electrostatic discharge

Additionally, circuitry called the can be used to reduce common-mode interference (typically the 50 or 60 Hz mains power).

right leg driver

ECG voltages measured across the body are very small. This low voltage necessitates a low circuit, instrumentation amplifiers, and electromagnetic shielding.

noise

Simultaneous lead recordings: earlier designs recorded each lead sequentially, but current models record multiple leads simultaneously.

Lead I is the voltage between the (positive) left arm (LA) electrode and right arm (RA) electrode:

depolarization of the heart toward the positive electrode produces a positive deflection

depolarization of the heart away from the positive electrode produces a negative deflection

repolarization of the heart toward the positive electrode produces a negative deflection

repolarization of the heart away from the positive electrode produces a positive deflection

and atrial flutter without rapid ventricular response

Atrial fibrillation

(PACs) and premature ventricular contraction (PVCs)

Premature atrial contraction

Sinus arrhythmia

and sinus tachycardia

Sinus bradycardia

and sinoatrial arrest

Sinus pause

and bradycardia-tachycardia syndrome

Sinus node dysfunction

Supraventricular tachycardia

Atrial fibrillation

Wide complex tachycardia

Ventricular flutter

Pre-excitation syndrome

Lown–Ganong–Levine syndrome

(Osborn wave)

J wave

Numerous diagnoses and findings can be made based upon electrocardiography, and many are discussed above. Overall, the diagnoses are made based on the patterns. For example, an "irregularly irregular" QRS complex without P waves is the hallmark of atrial fibrillation; however, other findings can be present as well, such as a bundle branch block that alters the shape of the QRS complexes. ECGs can be interpreted in isolation but should be applied – like all diagnostic tests – in the context of the patient. For example, an observation of peaked T waves is not sufficient to diagnose hyperkalemia; such a diagnosis should be verified by measuring the blood potassium level. Conversely, a discovery of hyperkalemia should be followed by an ECG for manifestations such as peaked T waves, widened QRS complexes, and loss of P waves. The following is an organized list of possible ECG-based diagnoses.[89]


Rhythm disturbances or arrhythmias:[90]


Heart block and conduction problems:


Electrolytes disturbances and intoxication:


Ischemia and infarction:


Structural:


Other phenomena:

In 1872, is reported to have attached wires to the wrist of a patient with fever to obtain an electronic record of their heartbeat.[92]

Alexander Muirhead

In 1882, working with frogs, was the first to appreciate that the interval between variations in potential was not electrically quiescent and coined the term "isoelectric interval" for this period.[93]

John Burdon-Sanderson

In 1887, [94] invented an ECG machine consisting of a Lippmann capillary electrometer fixed to a projector. The trace from the heartbeat was projected onto a photographic plate that was itself fixed to a toy train. This allowed a heartbeat to be recorded in real time.

Augustus Waller

In 1895, assigned the letters P, Q, R, S, and T to the deflections in the theoretical waveform he created using equations which corrected the actual waveform obtained by the capillary electrometer to compensate for the imprecision of that instrument. Using letters different from A, B, C, and D (the letters used for the capillary electrometer's waveform) facilitated comparison when the uncorrected and corrected lines were drawn on the same graph.[95] Einthoven probably chose the initial letter P to follow the example set by Descartes in geometry.[95] When a more precise waveform was obtained using the string galvanometer, which matched the corrected capillary electrometer waveform, he continued to use the letters P, Q, R, S, and T,[95] and these letters are still in use today. Einthoven also described the electrocardiographic features of a number of cardiovascular disorders.

Willem Einthoven

In 1897, the string galvanometer was invented by the French engineer .[96]

Clément Ader

In 1901, Einthoven, working in , the Netherlands, used the string galvanometer: the first practical ECG.[97] This device was much more sensitive than the capillary electrometer Waller used.

Leiden

In 1924, Einthoven was awarded the for his pioneering work in developing the ECG.[98]

Nobel Prize in Medicine

By 1927, General Electric had developed a portable apparatus that could produce electrocardiograms without the use of the string galvanometer. This device instead combined amplifier tubes similar to those used in a radio with an internal lamp and a moving mirror that directed the tracing of the electric pulses onto film.

[99]

In 1937, invented a new portable electrocardiograph machine.[100]

Taro Takemi

In 1942, Emanuel Goldberger increases the voltage of Wilson's unipolar leads by 50% and creates the augmented limb leads aVR, aVL and aVF. When added to Einthoven's three limb leads and the six chest leads we arrive at the 12-lead electrocardiogram that is used today.

[101]

In the late 1940s, invented an inkjet printer involving thin jets of ink deflected by electrical potentials from the heart, with good frequency response and direct recording of ECG on paper. The device, called the Mingograf, was sold by Siemens Elema until the 1990s.[102]

Rune Elmqvist

Signal-averaged electrocardiogram

Electrical conduction system of the heart

Electroencephalography

Electrogastrogram

Electropalatography

Electroretinography

Emergency medicine

Forward problem of electrocardiology

Heart rate

Heart rate monitor

KardiaMobile

Wireless ambulatory ECG

from ECGpedia, a wiki encyclopedia for a course on interpretation of ECG

The whole ECG course on 1 A4 paper

provided by Beth Israel Deaconess Medical Center

Wave Maven – a large database of practice ECG questions

PysioBank – a free scientific database with physiologic signals (here ecg)

EKG Academy – free EKG lectures, drills and quizzes

created by Eccles Health Sciences Library at University of Utah

ECG Learning Center