Electrocardiography is the process of producing an electrocardiogram, a recording – a graph of voltage versus time – of the electrical activity of the heart 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. Changes in the normal ECG pattern occur in numerous cardiac abnormalities, including cardiac rhythm disturbances, inadequate coronary artery blood flow, electrolyte disturbances. 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 measured from twelve different angles and is recorded over a period of time. In this way, the overall magnitude and direction of the heart's electrical depolarization is captured at each moment throughout the cardiac cycle. There are three main components to an ECG: the P wave, which represents the depolarization of the atria.

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, 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. 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. 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, the function of implanted pacemakers; the overall goal of performing an ECG is to obtain information about the electrical function of the heart. Medical uses for this information are varied and need to be combined with knowledge of the structure of the heart and physical examination signs to be interpreted.

Some indications for performing an ECG include the following: Chest pain or suspected myocardial infarction, such as ST elevated myocardial infarction or non-ST elevated myocardial infarction Symptoms such as shortness of breath, fainting, funny turns, or arrhythmias including new onset palpitations or monitoring of known cardiac arrhythmias Medication monitoring and management of overdose Electrolyte abnormalities, such as hyperkalemia Perioperative monitoring in which any form of anesthesia is involved. This includes intraoperative and postoperative monitoring. Cardiac stress testing Computed tomography angiography and magnetic resonance angiography of the heart Clinical cardiac electrophysiology, 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. ECGs can be recorded as continuous ECG monitoring. Continuous monitoring is used for critically ill patients, patients undergoing general anesthesia, patients who have an infrequently occurring cardiac arrhythmia that would unlikely be seen on a conventional ten-second ECG.

Continuous monitoring can be conducted by using Holter monitors and external defibrillators and pacemakers, and/or biotelemetry. Evidence does not support the use of ECGs among those without symptoms or at low risk of cardiovascular disease as an effort for prevention; this is because an ECG may falsely indicate the existence of a problem, leading to misdiagnosis, the recommendation of invasive procedures, overtreatment. However, persons employed in certain critical occupations, such as aircraft pilots, may be required to have an ECG as part of their routine health evaluations. Hypertrophic cardiomyopathy screening may be considered in adolescents as part of a sports physical out of concern for sudden cardiac death. Electrocardiographs are recorded by machines that consist of a set of electrodes connected to a central unit. 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 converters to convert the electrical activity of the heart to a digital signal.

Many ECG machines are now portable and include a screen and printer on a small wheeled cart. Recent advancements in electrocardiography include developing smaller devices for inclusion in fitness trackers and smart watches; these smaller devices rely on only two electrodes to deliver a single lead. Recording an ECG is a painless procedure; the machines are powered by mains power but they are designed with several safety features including an earthed 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 cal

Dane O'Neill is an Irish jockey, who has won over 1,700 races in Great Britain over a 25-year career, including the 2015 Commonwealth Cup at Royal Ascot. O'Neill brought up in Monkstown, County Cork, his uncle was a trainer, his family had always been interested in racing. He was a skilled showjumper in his youth, rode 24 winners in pony races, he moved to Britain aged 17 and spent his early career riding for Richard Hannon Sr.. His first winner was Port Sunlight, at Sandown Park on 15 July 1993. Winners were slow to come, in his first three seasons, he only rode seven, his career took a step forward in 1996 when he won the apprentice jockeys’ championship with 67 wins. For Hannon, he won several big sprint races on Bold Edge, including the Cork and Orrery Stakes at Royal Ascot and the Diadem Stakes in 1999 and his first Group 1, the Prix Maurice de Gheest in August 2000, he won the Jersey Stakes at the 1999 Royal Ascot on Lots of Magic. 2003 was his most successful year to date with 110 winners.

These included Airwave in the Group 2 Temple Stakesfor Henry Candy, another Royal Ascot winner, Macadamia in the Royal Hunt Cup for James Fanshawe. In total, he won over £1.3 million in prize money during the year. It was five years before he reached 100 winners or £1 million in prize money again, aided by wins in the Stewards' Cup for William Haggas on Conquest I, he spent a period as stable jockey to Henry Candy. In October 2012, he was appointed second jockey to Sheikh Hamdan al Maktoum, behind Paul Hanagan; the Maktoum partnership led him to the biggest prize of his career - the first Commonwealth Cup at Royal Ascot in 2015 on Muhaarar trained by Charlie Hills. On Mukhadram he finished third in the 2014 King George Queen Elizabeth Stakes. By the end of 2017, he had nearly 1,700 career victories in Britain, became the seventh most prolific winner among current jockeys on the retirement of Jimmy Fortune. Flat wins in Great Britain by year Great Britain Commonwealth Cup - Muhaarar Cork and Orrery Stakes - Bold Edge Diadem Stakes - Bold Edge France Prix Maurice de Gheest - Bold Edge

Hayley Marie Norman is an American actor and creator best known for her roles in Hancock, Chris Rock's Top Five, Adam Ruins Everything, Fired Up!, Norbit. She has written and starred in a number of online videos and sketches that have been featured by Funny or Die and collectively garnered millions of views; the digital series she produced and starred in, Hello Cupid, was accepted into Tribeca Film Festival and picked up by BET in 2015. Norman first became known as a case model on NBC's game show Deal or No Deal, where she was soon a fan favorite, she was so popular that the producers wrote an entire episode, titled "The Fro Show," around her signature hair, in addition to featuring her in several other episodes. She is the grandniece of Bobby Anderson. Born and raised in Thousand Oaks, California on March 3, 1984, Norman is of Russian, German and African-American descent, she began her career as a child, signing with her first agency at seven years old after being spotted in a restaurant by supermodel Cindy Crawford.

She traveled extensively to pursue modeling and acting, modeled for Mattel, doing a series of ads for the African-American Barbie doll. Norman is a graduate of the American Academy of Dramatic Arts in Los Angeles. In 2006, Norman joined the hit game show Deal or No Deal as Case Model #25, she remained on the show for three seasons while taking time off to act in various projects including Norbit, alongside Eddie Murphy and Cuba Gooding, Jr, as well as box office hit Hancock, in which she appeared with Will Smith. In 2008, she had a recurring role opposite Dennis Hopper on the Starz original series Crash, based on the Academy Award winning film; the following year, Norman appeared in the Screen Gems high school comedy Fired Up, for which Roger Ebert praised her performance as Angela. In 2011, Norman began racking up television credits, going on to recur on Adam Ruins Everything, The Game, ABC series Selfie, more, in addition to making a number of guest star appearances on shows like iZombie, The Soul Man, CSI: Miami, Bones.

In 2014, two feature films Norman acted in, Top Five and Beyond the Lights, both premiered at the 2014 Toronto International Film Festival. Top Five was written and directed by Chris Rock, who starred in the film. Hello Cupid, the web series that Norman produced and starred in, was accepted into Tribeca Film Festival in 2015; the semi-scripted series from Black&Sexy TV drew from Norman's improv and comedy skills and was spotlighted by Vulture, Teen Vogue, more. From 2015-2016, Norman recurred on IFC's Comedy Bang! Bang! and Jake and Amir's Vimeo series Lonely and Horny. Norman starred in the Das Racist music video for their song Girl in 2012. In 2018, Norman recurred on the Freeform series Alone Together, executive produced by The Lonely Island, appeared in the CBS sitcom Living Biblically, she will reprise her role as Marissa for the second season of Horny. In February 2018, Hayley booked a series regular role in the CW pilot Dead Inside from executive producer Bill Lawrence, she will portray the character of Jayla.

In August 2018, Hayley was asked to join the cast of NBC Universal's popular and long-running shows Access Live and Access Hollywood as a special guest host. Norman is a human rights activist touring the country as part of the Black History Mobile Museum speaking about gender and Hollywood. Norman is vocal about animal rights. Hayley Marie Norman on IMDb