Electrocardiography is a commonly used, non-invasive 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.
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.
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?
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.
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.
Method of tracing the electric current of a heartbeat to provide information on the heart. Electrocardiograms (ECGs) are made by applying electrodes, usually to the arms, legs, and chest wall, attached to an electrocardiograph, which records the tiny heart current. Upward and downward movements on the tracing reflect contractions of the atria and ventricles. Deviations from a standard point to a possible heart disorder and its site, as well as to possible high blood pressure and other diseases.
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.
The graphic recording from the body surface of the potential of electric currents generated by the heart, as a means of studying the action of the heart muscle. With the modern electrocardiograph, the current that accompanies the action of the heart is amplified 3000 times or more, and it moves a small, sensitively balanced lever in contact with moving paper. The pattern of heart waves that is traced on the paper indicates the heart's rhythm and other actions. The normal electrocardiogram is composed of a P wave, Q, R and S waves known as the qrs complex, or QRS wave, and a T wave. The P wave occurs at the beginning of each contraction of the atria. The QRS wave occurs at the beginning of each contraction of the ventricles. The T wave seen in a normal electrocardiogram occurs as the ventricles recover electrically and prepare for the next contraction. There is a refractory period after each P wave and QRS complex during which the muscle is inexcitable; this period is usually about 0.30 second. The electric impulses in the heart muscle are picked up and conducted to the electrocardiograph by electrodes or leads connected to the body by small metal plates or other methods. The metal plates are moistened with a conductive paste and attached to the limbs and chest (cardiac area) of the animal.
Electrocardiography: Normal lead II ECG complex. By permission from Morgan RV, Bright R, Swartout M, Handbook of Small Animal Practice, Saunders, 2002
