Electrocardiography
Electrocardiography
Definition
Purpose
Demographics
Description
Diagnosis/Preparation
Aftercare
Risks
Normal results
Morbidity and mortality rates
Alternatives
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.
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 relate to the electrical impulses produced at each beat of the heart.
Ectopic beat— Abnormal heart beat arising elsewhere than from the sinoatrial node.
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.
Reperfusion therapy— Restoration of blood flow to an organ or tissue; following a heart attack, quickly opening blocked arteries to reperfuse the heart muscles to minimize damage.
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 atria—the 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 node—commonly from the atria, atrioventricular node, or the ventricle. When these dys-rhythmias are only occasional, they may produce no symptoms or simply a feeling that the heart is turning over or “flip-flopping.” These occasional dysrhyth-mias 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
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.
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 impulses—at a rate of 60-100 times per minute—originate 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
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-the-counter medications as normal before my EKG or stress test?
- Should I refrain from eating before my stress test?
conjunction with an EKG include an echocardiogram (a sonogram of the heart’s pumping action) and a stress test—an EKG that is done in conjunction with treadmill or other supervised exercise to observe the heart’s function under stress—may also be performed.
Resources
BOOKS
Beasley, Brenda. Understanding EKGs: A Practical Approach, 2nd ed. Upper Saddle River, NJ: Prentice Hall, 2002.
PERIODICALS
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): 136–42.
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.
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
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 (1860–1927) 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 (1737–1798) and Italian physicist Alessandro Volta (1745–1827) 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 charge—either positive or negative—as 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 problems—like coronary artery blockage—do 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 ]
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 atria—the 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 node—commonly 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 impulses—at a rate of 60–100 times per minute—originate 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 test—an EKG that is done in conjunction with treadmill or other supervised exercise to observe the heart's function under stress—may 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): 136–42.
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?
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 impulses—at a rate of 60-100 times per minute—originate 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.
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 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 and is also used to evaluate symptoms such as chest pain , shortness of breath, and palpitations.
Precautions
No special precautions are required; however, patients are asked not to eat for several hours before a stress test .
Description
The patient disrobes from the waist up, and elec trodes (tiny wires in adhesive pads) are applied to specif ic sites on the arms, legs, and chest. When attached, these electrodes are called leads; three to twelve 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.
In 2001, the role of prehospital EKG in caring for patients with acute coronary syndromes was examined by the University of California San Diego School of Medicine, University of California San Diego Medical Center, San Diego, California, USA. Reported benefits of the prehospital 12-lead EKG include prompt initiation of reperfusion therapy (restoration of blood flow), and overall improved management and outcome of patients with acute myocardial infarction . Concerns remain regarding the best means of providing real-time field interpretation of the prehospital EKG and the potential for field time delay, triage concerns, and treatment of patients. Questions are raised regarding the overall clini cal and cost benefit of expanding this resource.
Preparation
The skin is cleaned to obtain good electrical contact at the electrode positions and, occasionally, shaving the chest may be necessary.
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 which relate to the electrical impulses produced at each beat of the heart.
Ectopic beat —Abnormal heart beat arising elsewhere than from the sinoatrial node.
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.
Reperfusion therapy —Restoration of blood flow to an organ or tissue; following a heart attack, quickly opening blocked arteries to reperfuse the heart muscles to minimize damage.
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.
Complications
No complications from this procedure have been observed.
Results
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, or 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 impulses—at a rate of 60–100 times per minute—originate 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.
Abnormal results
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 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 seconds).
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 simply a feeling that the heart is turning over or "flipflopping." 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, which begin in the ventricle, 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. 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.
Health care team roles
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 patients' 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.
Resources
BOOKS
Conover, Mary Boudreau. Understanding Electrocardiography. St Louis, MO: Mosby, 1996.
PERIODICALS
Crawford, Michael H. "Practice Guidelines for Ambulatory Electrocardiography" Journal of The American College of Cardiology 34, no. 3 (1999). Article available at <http://www.acc.org/media/media_journals.htm>.
Mangrum, J.M. "Tachyarrhythmias Associated With Acute Myocardial Infarction." In Emergency Medicine Clinics of North America 19, no. 2 (May 2001): 385-95.
Patel, R.J., G.M. Vilke, and T.C. Chan. "The Prehospital Electrocardiogram." Journal of Emergency Medicine 21, no. 1 (July 2001): 35-9.
ORGANIZATIONS
American Association of Critical-Care Nurses. 101 Columbia, Aliso Viejo, CA 92656-4109. (800) 899-2226. <http://www.aacn.org>.
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 75231-4596. (800) 242-1793. <http://www.amhrt.org>.
Maggie Boleyn, R.N., B.S.N.
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 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 and is also used to evaluate symptoms such as chest pain, shortness of breath, and palpitations.
Precautions
No special precautions are required; however, patients are asked not to eat for several hours before a stress test.
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 twelve 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.
In 2001, the role of prehospital EKG in caring for patients with acute coronary syndromes was examined by the University of California San Diego School of Medicine, University of California San Diego Medical Center, San Diego, California, USA. Reported benefits of the prehospital 12-lead EKG include prompt initiation of reperfusion therapy (restoration of blood flow), and overall improved management and outcome of patients with acute myocardial infarction. Concerns remain regarding the best means of providing real-time field interpretation of the prehospital EKG and the potential for field time delay, triage concerns, and treatment of patients. Questions are raised regarding the overall clinical and cost benefit of expanding this resource.
Preparation
The skin is cleaned to obtain good electrical contact at the electrode positions and, occasionally, shaving the chest may be necessary.
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.
Complications
No complications from this procedure have been observed.
Results
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, or 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 impulses—at a rate of 60-100 times per minute—originate 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.
Abnormal results
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 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 seconds).
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 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, which begin in the ventricle, 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. 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.
Health care team roles
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 patients' 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.
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 which relate to the electrical impulses produced at each beat of the heart.
Ectopic beat— Abnormal heart beat arising elsewhere than from the sinoatrial node.
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.
Reperfusion therapy— Restoration of blood flow to an organ or tissue; following a heart attack, quickly opening blocked arteries to reperfuse the heart muscles to minimize damage.
Resources
BOOKS
Conover, Mary Boudreau. Understanding Electrocardiography. St Louis, MO: Mosby, 2003.
PERIODICALS
Crawford, Michael H. "Practice Guidelines for Ambulatory Electrocardiography" Journal of The American College of Cardiology 34, no. 3 (1999). Article available at 〈http://www.acc.org/media/media_journals.htm〉.
Mangrum, J.M. "Tachyarrhythmias Associated With Acute Myocardial Infarction." In Emergency Medicine Clinics of North America 19, no. 2 (May 2001): 385-95.
Patel, R.J., G.M. Vilke, and T.C. Chan. "The Prehospital Electrocardiogram." Journal of Emergency Medicine 21, no. 1 (July 2001): 35-9.
ORGANIZATIONS
American Association of Critical-Care Nurses. 101 Columbia, Aliso Viejo, CA 92656-4109. (800) 899-2226. 〈http://www.aacn.org〉.
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 75231-4596. (800) 242-1793. 〈http://www.amhrt.org〉.
Electrocardiography
Electrocardiography
Definition
Electrocardiography is a non-invasive diagnostic procedure for evaluating heart health by recording electrical activity in the heart. The visual record of this electrical activity is called an electrocardiogram (EKG or ECG).
Purpose
The heart is a muscular organ that receives and pumps blood. The heart contains separate chambers and valves. Contraction of the separate chambers is controlled by a finely coordinated sequence of electrical activity that occurs with every heartbeat. The timing of the contraction of each chamber of the heart must be precise in order for each chamber to empty efficiently and completely.
Heart muscle contraction is controlled by intermittent electrical impulses generated by specialized pacemaker cells in one part of the heart. Each time these cells fire, the heart muscle begins to contract, but all parts of the heart muscle do not contract at the same time. Instead, the electrical impulses from the pacemaker cells travel in a steady progression to different areas, causing a rhythmic contraction of the entire heart. This electrical activity is recorded during an EKG and produces a graph that shows a regular pattern of peaks and valleys called waves. The waves in a single heartbeat of a normal EKG are named P, Q, R, S, and T, and follow in alphabetical order. When something interferes with blood flow to the heart, timing of the electrical impulses, transmission of the electrical signal within the heart, or response of the heart muscle to the electrical signals, these waves take on an abnormal appearance. Characteristic abnormalities in specific waves can indicate different causes of heart dysfunction.
Electrocardiography is a diagnostic procedure performed for the following reasons.
- when the individual has chest pain
- the physician hears abnormal heart sounds (heart murmurs)
- to determine if a heart attack is occurring
- to determine how much damage was done by a past heart attack
- to help diagnose heart arrhythmias
- when the individual has shortness of breath, dizziness, high cholesterol, hypertension (high blood pressure), or other symptoms of heart disease or a systemic disease that may be affecting heart function
- before and during surgery to see how well the heart is functioning
- to see the effect of therapeutic medications on the heart
- as part of a routine physical examination
Some physicians recommend having a baseline EKG performed around age 50 (or younger if there is a family history of heart disease) while the heart is still healthy. The baseline EKG is then used for comparative purposes should heart problems develop later.
Precautions
Some medications affect the electrical activity of the heart and can alter an EKG recording. Before having an EKG, individuals should discuss with their doctor all medications—prescription, over-the-counter, herbal remedies, and dietary supplements—that they are taking. Some medications may need to be discontinued a few days before the test to get an accurate recording.
Description
An EKG is a common, painless diagnostic procedure. It can be performed in a doctor's office, hospital, freestanding clinic, emergency room, or at bedside if an individual is too ill to be moved. EKGs are performed by a trained technologist, medical assistant, or nurse.
The procedure takes no more than 10 minutes. The patient removes clothing and jewelry from the upper body. The chest is cleaned; some men with heavy chest hair may need to be shaved. The patient lies on a table and electrodes are attached to the arms, legs, and chest with a bit of adhesive or gel. Usually 12 electrodes are used. The patient then remains motionless for a few minutes while the electrodes transmit electrical impulses from the heart to a graphing device and/or computer to produce a visual representation of these impulses. Once the recording is complete, the electrodes are removed, the chest is cleaned, and the patient either returns to normal activities, or remains in bed if other examinations or procedures are necessary.
Occasionally heart problems show up sporadically or only when the heart is working hard. In the case of intermittent symptoms, the patient may have ambulatory EKG monitoring for 24 or more hours. The patient wears electrodes under regular street clothes. The electrodes are connected to a Holter monitor or other device that records information about the heart beat continuously for 24 hours, or when the patient notices symptoms, while the patient goes about normal daily activities. This can be especially useful in detecting irregularities of the heartbeat, such as fibrillation or premature heart contractions.
If symptoms of heart dysfunction show up only when the heart is working hard, a stress EKG may be administered. In this case, the EKG is performed while the patient exercises under supervision on a treadmill or stationary bicycle. If the patient is too ill to exercise , drugs can be given that stimulate the heart to work harder.
QUESTIONS TO ASK YOUR DOCTOR
- Why am I having an EKG?
- When will I get the results of my EKG?
- Should I take my prescription and over-the-counter medications as normal before my EKG or stress test?
- Should I refrain from eating before my stress test?
Preparation
The doctor ordering the EKG will give specific instructions regarding the use of medications before the EKG. People having a stress EKG may be advised not to eat for a few hours before the test. Otherwise no special preparation is required.
Aftercare
No special aftercare is required. The individual should be able to resume normal activities immediately following the tests.
Complications
This is an extremely safe procedure; no complications are expected.
Results
Results of a standard EKG are available immediately. The results are interpreted by a cardiologist with special training in interpreting EKG wave patterns. Based on the results, the patient may be cleared of any heart abnormalities, a specific heart problem may be diagnosed, or additional tests, such as blood tests, chest x-ray, or echocardiogram , may be ordered to confirm the conditions suggested by the EKG.
Caregiver concerns
A trained technician, medical assistant, or nurse performs the EKG. A cardiologist interprets the EKG and determines what additional tests or treatments are necessary.
KEY TERMS
Ambulatory monitoring —EKG recording over a prolonged period during which the patient can move around.
Arrhythmia —An abnormal heart rhythm.
Atrium (plural Atria) —The right or left upper chamber 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.
Ventricle —Alower pumping chambers of the heart. There are two ventricles, right and left. The right ventricle pumps oxygen-poor blood to the lungs to be re-oxygenated. The left ventricle pumps oxygen-rich blood to the body.
Resources
BOOKS
Wagner, Galen S. Marriott's Practical Electrocardiography, 11th ed. Philadelphia: Lippincott Williams & Wilkins, 2008.
PERIODICALS
Klingfield, Paul, et al. “Recommendations for the Standardization and Interpretation of the Electrocardiogram.” Circulation. 115 (2007): 1306-1324. http://circ.ahajournals.org/cgi/content/full/115/10/1306.
OTHER
“Electrocardiogram.” WebMD. April 21, 2006 [cited February 26, 2008]. http://www.webmd.com/heart-disease/electrocardiogram.
“Electrocardiogram (ECG or EKG).” MedicineNet.com. August 25, 2006 [cited February 26, 2008]. http://www.medicinenet.com/electrocardiogram_ecg_or_ekg/article.htm.
“What Is an Electrocardiogram?” National Heart Blood and Lung Institute. [cited February 26, 2008]. http://www.nhlbi.nih.gov/health/dci/Diseases/ekg/ekg_what.html.
ORGANIZATIONS
American College of Cardiology, Heart House, 2400 N Street, NW, Washington, DC, 20037, (202) 375-6000, (800) 253-4636 x8603, (202) 375-7000, [email protected], http://www.acc.org.
American Heart Association, 7272 Greenville Avenue, Dallas, TX, 75231, (800) 242-8721, http://www.americanheart.org.
Tish Davidson A.M.
Electrocardiogram
Electrocardiogram
Definition
Purpose
Description
Preparation
Precautions
Side effects
Interactions
Definition
An electrocardiogram is a test that detects and records electrical activity of the heart. It is also called an EKG or ECG.
WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?
- An electrocardiogram is made by a physician, physician’s assistant, nurse, emergency medical technician or other allied health professional that has appropriate training.
Purpose
An electrocardiogram is used to detect and locate the source of heart irregularities.
Description
Electrical impulses are generated by specialized tissues in the heart called the sinoatrial node. These electrical impulses cause the muscles of the heart to contract generating heartbeats. The sinoatrial node is located in the right atrium. The electrical impulses travel from the right atrium to the left ventricle, casing the muscle to contract as they travel through the heart. As the heart contracts, it pumps blood out to the rest of the body. The electrical impulses can be detected by sensors. An electrocardiogram is a paper record of the electrical activity in the heart.
An electrocardiogram records how fast the heart beats. By recording many heartbeats in succession, the pattern and regularity of heartbeats can be observed. AN electrocardiogram records the strength and timing of the electrical impulses as they travel through each portion of the heart.
Many diseases of the heart cause changes in the pattern of electrical impulses that are generated. Recordings of these electrical impulses can help to diagnose many different heart problems. These include the following conditions.
- Interrupted or stopped heart beats (a heart attack)
- Changes in the flow of blood to the muscles of the heart
- Irregularities in heartbeats (either too fast or too slow)
- Changes in the force of pumping by the heart or the volume of blood pumped
- Changes in the thickness of heart muscles
- Changes in the size of any of the four chambers in the heart
- Evidence of birth defects in the heart
- Diseases affecting heart valves
- Changes in the speed of electrical impulses
QUESTIONS TO ASK YOUR DOCTOR
- Why is an electrocardiogram being obtained?
- Who will interpret the electrocardiogram?
Electrocardiogram recordings can assist in diagnosing a heart attack. Changes can be detected by comparing EKG tracings that are made at different times.
Preparation
An electrocardiogram requires minimal preparation. All drugs (prescription, over the counter, and herbal products) that have been used in the previous 24 to 48 hours should be disclosed. This is necessary as many such products can affect electrocardiograms.
Jewelry and clothing that contains metal should be removed.
Areas on the arms, legs, and chest where electrodes (small metal discs) are placed are cleaned. They may be shaved to provide a clean, smooth surface for attaching the electrode.
Disposable electrodes that require no preparation are most commonly used. These are attached to skin on the chest, arms and a leg. These are connected to the electrocardiogram recorder by wires.
Electrocardiograms only record electrical impulses generated by the body.
Precautions
Other than removing metal, no other precautions are needed prior to having an EKG test.
Side effects
The only known side effect of an electrocardiogram is slight pulling of skin when the electrodes are removed.
Interactions
Since an electrocardiogram only records and does not generate any electrical impulses, it does not interact with any bodily system or drugs.
KEY TERMS
Sinoatrial node— Specialized tissue in he right atrium that initiates electrical activity in the heart
Resources
BOOKS
Bickley, L. S., and P. G. Szilagyi. Bates’ Guide to Physical Examination and History Taking. 9th ed. Philadelphia: Lippincott Williams and Wilkins, 2007.
Jarvis, C. Physical Examination and Health Assessment. 5th ed. Philadelphia: Saunders, 2007.
Seidel. H. M., J. Ball, J. Dains, and W. Bennedict. Mosby’s Physical Examination Handbook. 6th ed. St. Louis: MOsby, 2006.
Swartz, M. H. Textbook of Physical Diagnosis: History and Examination. 5th ed. Philadelphia: Saunders, 2005.
PERIODICALS
Holmqvist, F., D. Husser, J. M. Tapanianen et al. “Intera-trial conduction can be accurately determined using standard 12-lead electrocardiography: Validation of P-wave morphology using electroanatomic mapping in man.” Heart Rhythm 5, no. 3 (2008): 413–418.
Nikus, K. C. “Electrocardiography.” Timely Topics I Medicine 11, (2007): E29–E37.
Silverman, M. E. “ Electrocardiographic-Clinical-Patho logic Sleuthing (by Dr. J. Willis Hurst).” American Journal of Cardiology 101, no. 4 (2008): 550–552.
Song, Z. Z. “Electrocardiography-synchronized multi-detector row CT of right ventricular function.” Radiology 246, no. 3 (2008): 986–988.
ORGANIZATIONS
American Academy of Family Physicians. 11400 Tomahawk Creek Parkway, Leawood, KS 66211-2672. (913) 906-6000. E-mail: [email protected]. http://www.aafp.org.
American Academy of Pediatrics. 141 Northwest Point Boulevard, Elk Grove Village, IL 60007-1098. (847) 434-4000; Fax: (847) 434-8000. E-mail: [email protected]. http://www.aap.org/default.htm.
American College of Physicians. 190 N Independence Mall West, Philadelphia, PA 19106-1572. (800) 523-1546, x2600, or (215) 351-2600. http://www.acponline.org.
American Medical Association. 515 N. State Street, Chicago, IL 60610. (312) 464-5000. http://www.ama-assn.org.
OTHER
American Heart Association. “Information about electrocardiography.” 2008 [cited February 24, 2008]. http://www.americanheart.org/presenter.jhtml?identifier=3004613.
Kid’s Health. “Information about electrocardiography.” 2008 [cited February 22, 2008]. http://www.kidshealth.org/parent/general/sick/ekg.html.
Merck Manual. “Information about electrocardiography.” 2008 [cited February 24, 2008]. http://www.merck.com/mmpe/sec05/ch047/ch047c.html.
National Library of Medicine. “Information about electrocardiography.” 2008 [cited February 25, 2008]. http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=cm.chapter.1019.
L. Fleming Fallon, Jr, MD, DrPH
electrocardiogram
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.
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.