Editing Electrocardiography (section)

==Electrocardiograph machines==
[[File:EKG sensor.jpg|thumb|220x220px|An ECG electrode]]

Electrocardiograms are recorded by machines that consist of a set of electrodes connected to a central unit.<ref>{{cite web|title=Electrocardiograph, ECG|publisher=World Health Organization|url=https://www.who.int/medical_devices/innovation/electrocardiograph.pdf|access-date=1 August 2020}}</ref> Early ECG machines were constructed with [[analog electronics]], where the signal drove a motor to print out the signal onto paper. Today, electrocardiographs use [[analog-to-digital converter]]s to convert the electrical activity of the heart to a [[digital signal]]. Many ECG machines are now portable and commonly include a screen, keyboard, and printer on a small wheeled cart. Recent advancements in electrocardiography include developing even smaller devices for inclusion in fitness trackers and [[Smartwatch|smart watches]].<ref>{{Cite news|url=https://www.technologyreview.com/lists/technologies/2019/|title=How we'll invent the future, by Bill Gates |work=MIT Technology Review|access-date=2019-04-01|language=en-US}}</ref> These smaller devices often rely on only two electrodes to deliver a single lead I.<ref>{{Cite news|url=https://techcrunch.com/2012/12/04/mobile-health-moves-forward-fda-approves-alivecors-heart-monitor-for-the-iphone/|title=FDA approves AliveCor heart monitor|work=Techcrunch|access-date=2018-08-25|language=en-US}}</ref> Portable twelve-lead devices powered by batteries are also available.

Recording an ECG is a safe and painless procedure.<ref>{{Cite web|url=https://stanfordhealthcare.org/medical-tests/e/ekg/risks.html |title=EKG Risks|website=Stanford Health Care|access-date=2019-04-01}}</ref> The machines are powered by [[mains power]] but they are designed with several safety features including an earthed (ground) lead.
Other features include:
* [[Defibrillation]] 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.
* [[Electrostatic discharge]] is similar to defibrillation discharge and requires voltage protection up to 18,000 volts.
* Additionally, circuitry called the [[Driven right leg circuit|right leg driver]] can be used to reduce [[common-mode interference]] (typically the 50 or 60&nbsp;Hz mains power).
* ECG voltages measured across the body are very small. This low voltage necessitates a low [[Noise (electronics)|noise]] circuit, [[instrumentation amplifier]]s, and [[electromagnetic shielding]].
* Simultaneous lead recordings: earlier designs recorded each lead sequentially, but current models record multiple leads simultaneously.

Most modern ECG machines include [[Automated ECG interpretation|automated interpretation]] [[algorithm]]s. This analysis calculates features such as the [[PR interval]], [[QT interval]], [[Correction for heart rate|corrected QT (QTc) interval]], PR axis, QRS axis, rhythm and more. The results from these automated algorithms are considered "preliminary" until verified and/or modified by expert interpretation. Despite recent advances, computer misinterpretation remains a significant problem and can result in clinical mismanagement.<ref>{{Cite journal|last1=Schläpfer|first1=J|last2=Wellens|first2=HJ|date=2017-08-29|title=Computer-Interpreted Electrocardiograms: Benefits and Limitations.|journal=Journal of the American College of Cardiology|volume=70|issue=9|pages=1183–1192|doi=10.1016/j.jacc.2017.07.723|pmid=28838369|doi-access=free}}</ref>

===Cardiac monitors===
Besides the standard electrocardiograph machine, there are other devices capable of recording ECG signals. Portable devices have existed since the [[Holter monitor]] was introduced in 1962.
Traditionally, these monitors have used electrodes with patches on the skin to record the ECG, but new devices can stick to the chest as a single patch without need for wires, developed by Zio (Zio XT), TZ Medical (Trident), [[Philips]] (BioTel) and BardyDx (CAM) among many others.
Implantable devices such as the [[artificial cardiac pacemaker]] and [[implantable cardioverter-defibrillator]] are capable of measuring a "far field" signal between the leads in the heart and the implanted battery/generator that resembles an ECG signal (technically, the signal recorded in the heart is called an [[electrogram]], which is interpreted differently).
Advancement of the Holter monitor became the [[implantable loop recorder]] that performs the same function but in an implantable device with batteries that last on the order of years.

Additionally, there are available various [[Arduino]] kits with ECG sensor modules and [[smartwatch]] devices that are capable of recording an ECG signal as well, such as with the 4th generation [[Apple Watch]], [[Samsung Galaxy Watch 4]] and newer devices.