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Electrocardiography

Electrocardiography

Definition

Electrocardiography is a commonly used, noninvasive procedure for recording electrical changes in the heart. The record, which is called an electrocardiogram (ECG or EKG), shows the series of waves that relate to the electrical impulses that occur during each beat of the heart. The results are printed on paper and/or displayed on a monitor to provide a visual representation of heart function. The waves in a normal record are named P, Q, R, S, and T, and follow in alphabetical order. The number of waves may vary, and other waves may be present.


Purpose

Electrocardiography is a starting point for detecting many cardiac problems, including angina pectoris, stable angina, ischemic heart disease, arrhythmias (irregular heartbeat), tachycardia (fast heartbeat), bradycardia (slow heartbeat), myocardial infarction (heart attack), and certain congenital heart conditions. It is used routinely in physical examinations and for monitoring a patient's condition during and after surgery, as well as in the intensive care setting. It is the basic measurement used in exercise tolerance tests (i.e., stress tests) and is also used to evaluate symptoms such as chest pain, shortness of breath, and palpitations.


Demographics

According to the U.S. Centers for Disease Control (CDC), nearly 23 million EKG procedures were performed in doctor's offices in the year 2000.

Men are more likely to experience heart attacks than women, although a woman's risk of heart attack rises after menopause. African-Americans, Hispanics, and Native Americans are all at greater risk for cardiovascular disease than Caucasians, in part because of the higher incidence of diabetes mellitus (a major risk factor for cardiovascular disease) in these populations.



Description

The patient disrobes from the waist up, and electrodes (tiny wires in adhesive pads) are applied to specific sites on the arms, legs, and chest. When attached, these electrodes are called leads; three to 12 leads may be employed for the procedure.

Muscle movement may interfere with the recording, which lasts for several beats of the heart. In cases where rhythm disturbances are suspected to be infrequent, the patient may wear a small Holter monitor in order to record continuously over a 24-hour period. This is known as ambulatory monitoring.

Special training is required for interpretation of the electrocardiogram. To summarize in the simplest manner the features used in interpretations, the P wave of the electrocardiogram is associated with the contraction of the atriathe two chambers of the heart that receive blood from the veins. The QRS series of waves, or QRS complex, is associated with ventricular contraction, with the T wave coming after the contraction. The ventricles are the two chambers of the heart that receive blood from the atria and that send the blood into the arteries. Finally, the P-Q or P-R interval gives a value for the time taken for the electrical impulse to travel from the atria to the ventricle (normally less than 0.2 seconds).


Diagnosis/Preparation

Patients are asked not to eat for several hours before a stress test . Before the leads are attached, the skin is cleaned to obtain good electrical contact at the electrode positions and, occasionally, shaving the chest may be necessary.

Heart problems are diagnosed by the pattern of electrical waves produced during the EKG, and an abnormal rhythm can be called dysrhythmia. The cause of dysrhythmia is ectopic beats. Ectopic beats are premature heartbeats that arise from a site other than the sinus nodecommonly from the atria, atrioventricular node, or the ventricle. When these dysrhythmias are only occasional, they may produce no symptoms or simply a feeling that the heart is turning over or "flip-flopping." These occasional dysrhythmias are common in healthy people, but they also can be an indication of heart disease.

The varied sources of dysrhythmias provide a wide range of alterations in the form of the electrocardiogram. Ectopic beats display an abnormal QRS complex. This can indicate disease associated with insufficient blood supply to the heart muscle (myocardial ischemia). Multiple ectopic sites lead to rapid and uncoordinated contractions of the atria or ventricles. This condition is known as fibrillation. When the atrial impulse fails to reach the ventricle, a condition known as heart block results.


Aftercare

To avoid skin irritation from the salty gel used to obtain good electrical contact, the skin should be thoroughly cleaned after removal of the electrodes.


Risks

The EKG is a noninvasive procedure that is virtually risk-free for the patient. There is a slight risk of heart attack for individuals undergoing a stress test EKG, but patients are carefully screened for their suitability for this test before it is prescribed.

Risk factors for heart disease include obesity, hypertension (high blood pressure), high triglycerides and total blood cholesterol, low HDL ("good") cholesterol, tobacco smoking, and increased age. People who have diabetes mellitus (either type 1 or type 2) are also at increased risk for cardiovascular disease.


Normal results

When the heart is operating normally, each part contracts in a specific order. Contraction of the muscle is triggered by an electrical impulse. These electrical impulses travel through specialized cells that form a conduction system. Following this pathway ensures that contractions will occur in a coordinated manner.

When the presence of all waves is observed in the electrocardiogram, and these waves follow the order defined alphabetically, the heart is said to show a normal sinus rhythm, and impulses may be assumed to be following the regular conduction pathway.

In the normal heart, electrical impulsesat a rate of 60100 times per minuteoriginate in the sinus node. The sinus node is located in the first chamber of the heart, known as the right atrium, where blood reenters the heart after circulating through the body. After traveling down to the junction between the upper and lower chambers, the signal stimulates the atrioventricular node. From here, after a delay, it passes by specialized routes through the lower chambers or ventricles. In many disease states, the passage of the electrical impulse can be interrupted in a variety of ways, causing the heart to perform less efficiently.

The heart is described as showing arrhythmia or dysrhythmia when time intervals between waves, or the order or the number of waves do not fit the normal pattern described above. Other features that may be altered include the direction of wave deflection and wave widths.

Morbidity and mortality rates

According to the American Heart Association, cardiovascular disease is the number one cause of death in the United States. It is also the leading cause of death among people with diabetes.


Alternatives

Electrocardiography is the gold standard for detecting heart conditions involving irregularities in electrical conduction and rhythm. Other tests that may be used in conjunction with an EKG include an echocardiogram (a sonogram of the heart's pumping action) and a stress testan EKG that is done in conjunction with treadmill or other supervised exercise to observe the heart's function under stressmay also be performed.


Resources

books

beasley, brenda. understanding ekgs: a practical approach. 2nd ed. upper saddle river, nj: prentice hall, 2002.


periodicals

kadish, alan, et al. "acc/aha clinical competence statement on electrocardiography and ambulatory electrocardiography." journal of the american college of cardiology 38, no. 7 (2001). <http://www.acc.org/clinical/competence/ecg/pdfs/ecg_pdf.pdf.>.

fergusun, j. d., et al. "the prehospital 12-lead electrocardiogram: impact on management of the out-of-hospital acute coronary syndrome patient." american journal of emergency medicine 21, no. 2 (march 2003): 13642.

organizations

the american college of cardiology. heart house, 9111 old georgetown road, bethesda, md 20814-1699. (800) 253-4636. <http://www.acc.org>.

american heart association. 7272 greenville ave., dallas, tx 75231. (800) 242-8721. <http://www.americanheart.org>.


Maggie Boleyn, R.N., B.S.N. Paula Ford-Martin

WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?


The electrocardiograph is conducted by a fully trained technologist and may be done in the cardiologist's office, a testing facility, or at a hospital patient's bedside. The technologist, or perhaps a nurse or nurse practitioner, will take the patient's medical history, educate them about the procedure they are about to undergo, and help them relax. The results of the electrocardiograph will be interpreted by a qualified physician, usually a cardiologist.

QUESTIONS TO ASK THE DOCTOR


  • Why has an EKG been prescribed for me?
  • When will I get the results of my EKG?
  • Should I take my prescription and over-thecounter medications as normal before my EKG or stress test?
  • Should I refrain from eating before my stress test?

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"Electrocardiography." Gale Encyclopedia of Surgery: A Guide for Patients and Caregivers. . Encyclopedia.com. 22 Aug. 2017 <http://www.encyclopedia.com>.

"Electrocardiography." Gale Encyclopedia of Surgery: A Guide for Patients and Caregivers. . Encyclopedia.com. (August 22, 2017). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/electrocardiography

"Electrocardiography." Gale Encyclopedia of Surgery: A Guide for Patients and Caregivers. . Retrieved August 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/electrocardiography

Electrocardiogram

Electrocardiogram

An electrocardiogram (pronounced ee-lek-troe-KAR-dee-oh-gram) is a recording of the electrical activity within the heart that is obtained by placing various electrodes on the skin surface. From this painless, quick, and inexpensive test, doctors are able to evaluate a person's heart rate and rhythm and to detect if something is wrong.

Normal and abnormal wave patterns

An electrocardiogram, better known as an EKG or ECG, is a common test doctors use to obtain information about the overall health of a patient's heart. Using a machine called an electrocardiograph, the physician is able to see a real-time image of the electrical activity going on in the heart. Usually the doctor examines a printed pattern of heart activity that is recorded on a moving strip of paper, but he or she may also view the pattern on a television-like screen. By examining this pattern of waves, the physician views an actual picture of the heart's rhythm and can then detect many heart problems. Since a normal, healthy heart makes a specific pattern of waves, a damaged or diseased heart changes that pattern in recognizable ways. Simply by examining the EKG, a physician can detect and analyze something like an abnormal or irregular heart rhythm known as an arrhythmia (pronounced uh-RITH-mee-uh). The physician can also identify areas of the heart muscle that have been damaged by coronary heart disease, high blood pressure, rheumatic fever, or birth defects. A previous heart attack will also show up on the pattern, and follow-up EKGs will show if the heart is recovering from it. An EKG also may be used to determine the effect of certain drugs on the heart, and is sometimes used to test how an implanted pacemaker is working.

First EKG

Physicians have not always been able to learn so much about the heart by viewing a simple printout of its electrical activity. The technique known as electrocardiography (pronounced ee-lek-troe-kar-dee-AH-gruhfee) was first reported in 1901. In that year, Dutch physiologist William Einthoven (18601927) published a report documenting his invention of what was called the "string galvanometer." Einthoven was able to design such a device more than a hundred years ago because scientists knew by then that there was some sort of electrical activity going on in the heart. Earlier research done by Italian anatomist Luigi Galvani (17371798) and Italian physicist Alessandro Volta (17451827) had proven that electricity does exist in living tissue. Although many had tried before him, Einthoven was the first to devise the best method for recording the electrical activity of the heart.

Electricity in living tissue

Although Galvani was able to demonstrate with his 1794 experiments the existence of electricity in living tissue, it was not until 1834 that anyone was able to record and measure that force. Even then, however, another three generations would pass before Einthoven was able to construct a reliable, practical system. The first EKG was introduced to the United States in 1909, and in 1924, Einthoven was awarded the Nobel Prize for physiology or medicine. Both Einthoven's system and the one used today are based on the fact that each time the heart beats, it produces electrical currents. It is these currents that actually make the heart contract or pump the blood that each cell in the body needs to stay alive and do its work.

Words to Know

Arrhythmia: An irregular beating of the heart.

Depolarization: The tendency of a cell membrane when stimulated to allow ions to enter or leave the cell.

Ion: An atom or groups of atoms that carries an electrical chargeeither positive or negativeas a result of losing or gaining one or more electrons.

In fact, every muscle and nerve cell is capable of producing a tiny electrical signal through a process called "depolarization." This means that in each cell, charged atomic particles called positive and negative ions are moving in and out of its membrane, and it is this movement that creates electrical currents. Therefore, an EKG is not a measurement of the heart's muscular activity but rather a measurement of the flow of ions (or the electrical current) through the membranes of the heart muscle before it contracts. Since a person's body is made up mainly of salty water, it is an excellent conductor of electricity and these currents can be detected at the surface of the skin.

Taking an EKG

Before an EKG is taken, electrodes or conducting plates are attached to the skin in certain areas. The electrodes are then connected by wires to a meter that boosts or amplifies the impulses, either recording them on a piece of paper using a pen attached to the meter or displaying them on some sort of monitor. During an EKG, a patient will usually have electrodes connected at both wrists and ankles as well as at six other points on the chest, roughly over the area of the heart. The electrodes are attached to the skin with sticky pads or suction cups. Sometimes a gel that helps conduction is applied to the skin before the electrodes are attached. Each of these electrode wires or "leads" is connected to the meter or the recording part of the EKG machine, and each wire registers a pattern of electrical impulses and displays it on a graph.

From the patient's point of view, he or she is usually lying down and is asked to remain still while the leads are attached as well as for the duration of the test. The entire recording is usually completed in five to ten minutes and requires nothing more of the patient. This test is painless, noninvasive, and it has no associated risks. There is absolutely no danger since the electricity involved comes from the patient's own heart, which then flows into the machine. No electricity ever passes from the machine into the patient. Whether recorded on a paper graph or on a monitor, the wavelike image produced is usually a small blip followed by a big blip. Although this pattern may look the same to the average person, the informed and trained eye of the professional can tell a great deal about the patient's heart according to how that pattern differs from the normal pattern.

Other types

Since doctors know that certain types of heart problemslike coronary artery blockagedo not show up on a resting EKG, they often prescribe a stress EKG to make sure that no condition goes undetected. For this test, the leads are attached the same way, but the patient is asked to exercise strenuously, usually on a treadmill machine. Since the heart requires a larger supply of blood while exercising, a stress EKG provides a more complete and accurate diagnosis than a resting EKG. Although patients usually

have to go to a doctor's office for a stress EKG, resting EKG machines are small and portable and can be done in the home by a technician. EKG data can also be transmitted by using radiotelemetry techniques. Also called a transtelephonic EKG (pronounced tranz-tell-eh-FON-ik), this technology allows outpatient heart data to be transmitted to a hospital or wherever a doctor chooses.

Finally, EKGs can also be done continuously. In certain cases when a patient's heart problem arises only now and then, the doctor will request that a Holter monitor be worn while the patient goes about his or her normal day. This monitor has an amplifier and a cassette tape that

records the patient's EKG pattern. The monitor is sometimes worn for as long as forty-eight hours. The patient is also asked to keep track of any unusual activities or even emotional states that might affect his or her heart's rhythm.

[See also Heart ]

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electrocardiogram

electrocardiogram This means of studying the activity of the heart from electrical signals detectable from the body surface stemmed directly, early in the twentieth century, from the invention of the string galvanometer by the Dutch physiologist, Einthoven. Electrocardiography was demonstrated to the Royal Society in London in 1909.

The ‘ECG’ (or sometimes still ‘EKG’ in the US, from the German spelling) has become an icon representing the heart's activity. The waveform is the most familiar ‘high tech’ sign of the electrical behaviour of the heart. In various versions, its characteristic shape (see figure) reporting a healthy rhythm, or the flat line suggesting the patient's demise, is familiar to any viewer of television medical soap operas. A clever variation on the theme forms the distinctive logo for the British Heart Foundation, the largest UK charity dedicated to funding cardiovascular research.

The electrocardiogram (as a paper trace or a TV monitor display) shows the changes in the voltage, detectable during the time course of the heart beat, between pairs of electrodes placed at certain points on the skin. The basis of the ECG is that the heart, like other muscles, is triggered to contract by electrical activity. The heart is a relatively large piece of tissue, so the flow of electrical current associated with (and immediately preceding) contraction produces detectable voltages (typically a few millivolts) on the surface of the body. Electrode pairs can be placed at various positions on the body to yield information about the status of the heart. The classic ‘limb leads’ are attached to one leg and two arms; other pairings are placed at defined positions on the chest itself. Even more detail can be obtained with leads inserted in the oesophagus (the gullet) or even from within the heart itself (with the electrode introduced via a vein). Abnormal enlargement (hypertrophy) of the heart's various chambers produces characteristic distortions of the ‘ideal’ ECG form which are readily interpreted by experienced users.

The spread of the electrical wave across the heart varies in speed (see heart). Simple physics dictates that where a change in potential of a large fraction of the heart occurs in a relatively brief time, the resulting ECG wave is large too. When most of the heart is at a similar potential, no voltage difference will appear at the surface. Thus, prominent waves in the ECG indicate the synchronized start (or finish) of activity in significant fractions of the heart.

These potentials amount to one or two milli-volts. The impulse of electrical activity causing the heart to contract in a co-ordinated manner progresses through the heart in a complex three-dimensional pattern. The appearance of the electrocardiogram, therefore, varies from person to person as heart shape and position can be significantly different even in entirely normal individuals. Any person's pattern further alters with the location of the recording electrodes. Nevertheless, there are significant, consistently observed deflections and intervals in a typical electrocardiogram; the main ‘peaks’ are labelled as P, QRS, and T (see figure).

The most basic feature of the ECG is that the time from any one such ‘peak’ to the same one in the next cycle indicates precisely how long the heart cycle is taking. At slow rates, the timing of the waves can be easily correlated to the heart sounds heard with the stethoscope. But far more precise information can be gleaned once the relationship of the waves to the phases of the cycle is understood:

The P-wave

indicates the electrical activity associated with contraction of the cardiac atria, the heart's upper chambers.

The P–R interval

is the delay between the beginning of activity in the atria and the ventricles (atrio–ventricular conduction time). In adults, normal P–R intervals range between 120 and 200 milliseconds, occasionally being shorter in children and slightly longer in the aged. The P–R interval shortens at high heart rates (e.g. due to exercise or to fever) and increases at lower heart rates (e.g. during sleep).

The QRS complex

indicates the onset of contraction of the ventricles. The shape of the QRS complex may be modified by a number of physiological factors (e.g. body position and breathing pattern). In normal adults, the duration of the QRS complex varies between 60 and 100 milliseconds; in children it tends to be shorter.

The Q–T interval

is measured from the beginning of the QRS complex to the end of the T-wave and represents the time between activation of electrical activity in the ventricles and their return to the resting state. Like the P–R interval, the Q–T interval shortens at high heart rates and increases at lower rates.

The T-wave

indicates when the electrical activity associated with the cells in the cardiac ventricle returns to the resting state after electrical activation. Thus, it signals the start of relaxation of the ventricle walls. It tends to be longer lasting than QRS because the onset of relaxation across the ventricle is less tightly synchronized than that of contraction.

Some stark deviations from this classical sequence can occur, including the chaotic waves associated with ventricular fibrillation. This is the uncoordinated, apparently random electrical activity (and thus contraction) of the ventricles that can readily prove fatal without defibrillation. Heart block is a condition readily identified by ECG analysis.

There are characteristic changes in the wave pattern of the ECG in myocardial ischaemia (inadequate blood supply to the heart), which may be evident at first during exercise in sufferers from angina, and which may confirm or exclude an ischaemic episode or myocardial infarction in instances of unexplained chest pain.

David J. Miller, and Niall G. MacFarlane


See also heart; heart attack.

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Electrocardiography

Electrocardiography

Definition

Electrocardiography is a commonly used, noninvasive procedure for recording electrical changes in the heart. The record, which is called an electrocardiogram (ECG or EKG), shows the series of waves that relate to the electrical impulses which occur during each beat of the heart. The results are printed on paper or displayed on a monitor. The waves in a normal record are named P, Q, R, S, and T and follow in alphabetical order. The number of waves may vary, and other waves may be present.

Purpose

Electrocardiography is a starting point for detecting many cardiac problems. It is used routinely in physical examinations and for monitoring the patient's condition during and after surgery, as well as during intensive care. It is the basic measurement used for tests such as exercise tolerance. It is used to evaluate causes of symptoms such as chest pain, shortness of breath, and palpitations.

Precautions

No special precautions are required.

Description

The patient disrobes from the waist up, and electrodes (tiny wires in adhesive pads) are applied to specific sites on the arms, legs, and chest. When attached, the electrodes are called leads; three to 12 leads may be employed.

Muscle movement may interfere with the recording, which lasts for several beats of the heart. In cases where rhythm disturbances are suspected to be infrequent, the patient may wear a small Holter monitor in order to record continuously over a 24-hour period; this is known as ambulatory monitoring.

Preparation

The skin is cleaned to obtain good electrical contact at the electrode positions.

Aftercare

To avoid skin irritation from the salty gel used to obtain good electrical contact, the skin should be thoroughly cleaned after removal of the electrodes.

Risks

No complications from this procedure have been observed.

Normal results

When the heart is operating normally, each part contracts in a specific order. Contraction of the muscle is triggered by an electrical impulse. These electrical impulses travel through specialized cells that form a conduction system. Following this pathway ensures that contractions will occur in a coordinated manner.

When the presence of all waves is observed in the electrocardiogram and these waves follow the order defined alphabetically, the heart is said to show a normal sinus rhythm, and impulses may be assumed to be following the regular conduction pathway.

The heart is described as showing arrhythmia or dysrhythmia when time intervals between waves, the order, or the number of waves do not fit this pattern. Other features that may be altered include the direction of wave deflection and wave widths.

In the normal heart, electrical impulsesat a rate of 60-100 times per minuteoriginate in the sinus node. The sinus node is located in the first chamber, known as the right atrium, where blood re-enters the heart. After traveling down to the junction between the upper and lower chambers, the signal stimulates the atrioventricular node. From here, after a delay, it passes by specialized routes through the lower chambers or ventricles. In many disease states, the passage of the electrical impulse can be interrupted in a variety of ways, causing the heart to perform less efficiently.

Abnormal results

Special training is required for interpretation of the electrocardiogram. To summarize the features used in interpretations in the simplest manner, the P wave of the electrocardiogram is associated with the contraction of the atria. The QRS series of waves, or QRS complex, is associated with ventricular contraction, with the T wave coming after the contraction. Finally, the P-Q or P-R interval gives a value for the time taken for the electrical impulse to travel from the atria to the ventricle (normally less than 0.2 sec).

The cause of dysrhythmia is ectopic beats. Ectopic beats are premature heart beats that arise from a site other than the sinus node-commonly from the atria, atrioventricular node, or the ventricle. When these dysrhythmias are only occasional, they may produce no symptoms, or a feeling of the heart turning over or "flip-flopping" may be experienced. These occasional dysrhythmias are common in healthy people, but they also can be an indication of heart disease.

The varied sources of dysrhythmias provide a wide range of alterations in the form of the electrocardiogram. Ectopic beats that start in the ventricle display an abnormal QRS complex. This can indicate disease associated with insufficient blood supply to the muscle (myocardial ischemia). Multiple ectopic sites lead to rapid and uncoordinated contractions of the atria or ventricles. This condition is known as fibrillation. In atrial fibrillation, P waves are absent, and the QRS complex appears at erratic intervals, or "irregularly irregular."

When the atrial impulse fails to reach the ventricle, a condition known as heart block results. If this is partial, the P-R interval (the time for the impulse to reach the ventricle) is prolonged. If complete, the ventricles beat independently of the atria at about 40 beats per minute, and the QRS complex is mostly dissociated from the P wave.

Resources

ORGANIZATIONS

American Heart Association. 7320 Greenville Ave. Dallas, TX 75231. (214) 373-6300. http://www.americanheart.org.

KEY TERMS

Ambulatory monitoring ECG recording over a prolonged period during which the patient can move around.

Arrhythmia or dysrhythmia Abnormal rhythm in hearts that contract in an irregular way.

ECG or EKG A record of the waves that relates to the electrical impulses produced at each beat of the heart.

Electrodes Tiny wires in adhesive pads that are applied to the body for ECG measurement.

Fibrillation Rapid, uncoordinated contractions of the upper or the lower chambers of the heart.

Lead Name given the electrode when it is attached to the skin.

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electrocardiography

electrocardiography (Ĭlĕk´trōkärdēŏg´rəfē), science of recording and interpreting the electrical activity that precedes and is a measure of the action of heart muscles. Since 1887, when Augustus Waller demonstrated the possibility of measuring such action, physicians and physiologists have recorded it in order to study the heart's normal behavior and to provide a method for diagnosing abnormalities. Electrical current associated with contraction of the heart muscles passes through the various tissues and reaches the surface of the body. What is actually recorded is the change in electrical potential on the body surface. The first practical device for recording the activity of the heart was the string galvanometer developed by William Einthoven in 1903. In this device a fine quartz string is suspended vertically between the poles of a magnet. The string is deflected in response to changes in electrical potential and its movement can be optically enlarged and photographed, or, if an immediately visible record is desired, the string's movement can be recorded on a sheet of paper. A more sophisticated form of the electrocardiograph employs a vacuum-tube amplifier. The greatly amplified current from the body deflects a mirror galvanometer that causes a beam of light to move across a light-sensitive film. When an electrocardiograph is taken, electrodes (leads) are attached to the extremities and to the left chest. The recordings obtained in this manner are called electrocardiograms, or more simply EKG's or ECG's. A normal EKG shows a sequence of three waves arbitrarily labeled P, QRS, and T. The P wave is a small, low-amplitude wave produced by the excitation of the atria of the heart. It is followed by a resting interval that marks the passage of electrical impulses into the ventricles. Following this interval comes the QRS wave, a rapid, high-amplitude wave marking ventricular excitation, and then a slow-building T wave denoting ventricular recovery. Abnormalities may be noted from deviation in wave form, height, direction, or duration. The type of abnormal wave may sometimes indicate the type of heart disorder. Usually the physician must associate the EKG with other clinical observations to determine the cause of the abnormality. See also stress test.

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Electrocardiograph (ECG)

Electrocardiograph (ECG)

In the late 1700s medical researchers learned that muscular contractions produce tiny electric currents. Research scientists reasoned that a recording of the electric impulses of the heart could reveal irregularities and, hence, heart disease. The Italian biophysicist Carlo Matteucci (1811-1868) observed electric impulses from a pigeon's heart in 1843. In 1856 the German scientists Rudolf Albert von Kolliker (1817-1905) and Heinrich Muller (1820-1864) recorded electric currents produced by a frog's heart.

The Measuring Device

Researchers attempted to develop accurate measuring devices. French physiologist Augustus Waller (1856-1922) found that cardiac currents could be recorded by placing surface electrodes on the body. Waller used a capillary electrometer. This device consisted of tubes of mercury that rose and fell with the changes in heart muscle current.

Dutch physiologist Willem Einthoven (1860-1927) set out to design an improved apparatus and in 1903 he described the results, a string galvanometer. The galvanometer consisted of a thin silver-coated quartz wire stretched between the poles of a magnet. As electric current flowed through, the wire was deflected. The magnified motion was projected onto moving photographic film. The extreme sensitivity of the device allowed it to detect the tiny cardiac currents very accurately.

Einthoven called his machine the electrocardiograph and the recorded electrical impulses an electrocardiogram. He devised the standard positioning of the electrodes on the human body. He also described the regular heart waves and the method used to interpret electrocardiograms. Through clinical studies, Einthoven identified a number of heart problems with his galvanometer. English physician Sir Thomas Lewis (1881-1945) established the electrocardiogram as a standard clinical tool.

With refinements in instrumentation and technique, electrocardiography became one of the most useful diagnostic tools in medicine. It is highly accurate, easy to interpret, and relatively inexpensive. Electrocardiography permits diagnosis of heart conditions without needles or incisions, and has pointed the way to similar diagnosis of brain currents.

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Electrocardiography

ELECTROCARDIOGRAPHY

The electrocardiogram (ECG) displays important information about the heart, including the occurrence of a heart attack or lack of oxygen, whether conduction of the heartbeat is disturbed, or its rate or rhythm altered. It is useful as a rapid indicator of the diagnosis and it is easy, painless, and inexpensive to record. The record made in healthy people at rest, or undergoing an exercise test, helps predict risk of future heart problems. It is also used to monitor severely ill patients.

The electrocardiograph was invented by Wilhelm Einthoven in Leiden, the Netherlands, around 1900. Einthoven measured the small differences in electrical potential between the arms and legs by amplifying the tiny current passing through the body with each heartbeat. In the twenty-first century, data about heart function are recorded from the chest wall and the limbs with the electrocardiograph and displayed on paper or TV screens as the ECG, an electrical recording, or tracing, of the heartbeat. This tracing is interpreted by physicians or technicians and, in digital form, is analyzed automatically with computers.

Henry Blackburn

(see also: Atherosclerosis; Cardiovascular Diseases; Coronary Artery Disease )

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electrocardiography

electrocardiography (i-lek-troh-kar-di-og-răfi) n. a technique for recording the electrical activity of the heart. Electrodes connected to the recording apparatus (electrocardiograph) are placed on the skin of the four limbs and chest wall; the record itself is called an electrocardiogram (ECG).

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electrocardiogram

electrocardiogram (ECG) A tracing or graph of the electrical activity of the heart. Recordings are made from electrodes fastened over the heart and usually on both arms and a leg. Changes in the normal pattern of an ECG may indicate heart irregularities or disease.

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electrocardiogram

e·lec·tro·car·di·o·gram / iˌlektrōˈkärdēəˌgram/ (abbr.: ECG or EKG) • n. Med. a record or display of a person's heartbeat produced by electrocardiography.

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electrocardiogram

electrocardiogram (ECG) (i-lek-troh-kar-di-oh-gram) n. a tracing of the electrical activity of the heart recorded by electrocardiography. It aids in the diagnosis of heart disease, which may produce characteristic changes in the ECG.

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electrocardiograph

e·lec·tro·car·di·o·graph / iˌlektrōˈkärdiəˌgraf/ (abbr.: ECG or EKG) • n. a machine used for electrocardiography.

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electrocardiogram

electrocardiogram (ECG) Recording of the electrical activity of the heart, traced on a moving strip of paper by an electrocardiograph. It is used to diagnose heart disease.

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electrocardiogram

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