Indications and Procedures
Electrocardiography is a useful medical diagnostic and evaluative procedure that reveals much information about the function or malfunction of a person’s heart. ECG is a noninvasive, easy-to-use, and economical tool that is an essential part of diagnosing chest pain. It serves an important role in both cardiology and emergency medicine. ECG is also commonly used in preventive medicine to monitor heart health. For this purpose, ECG is frequently used in a format known as a stress test. Athletes often have ECG analysis performed as a part of their training and cardiovascular conditioning.
In a stress test, a person is studied for regularity of rhythm, rate, and unimpeded flow of electrical conduction within the heart. ECG recordings are first made while the person is at rest, then during light exercise, and, finally, if healthy enough, during rigorous exercise. Such exercise causes the heart to work harder and allows a physician to determine whether a person has a heart that beats with a regular, repetitive rhythm and at an appropriate pace for the level of rest or exercise. The stress of exercise
can also help in assessing whether the heart muscle masses contract in the proper sequence: atrial contraction followed by ventricular contraction. An irregularity of electrical conduction, poor muscle contraction, dead regions of heart tissue (from a recent or old heart attack), and other maladies can be revealed.
To obtain an electrocardiogram, small metallic contact points are taped to the patient’s skin via an electrically conductive adhesive or gel. The electric impulses travel across the skin to these contact points; from there, leads (plastic-coated wires) are attached to the recording device so that a complete circuit is made. Either a monitor screen or a strip chart recorder traces the electrical impulses. The waves are plotted in units of millivolts (on the y-axis) versus time in units of seconds (on the x-axis).
A twelve-lead ECG has replaced the original four-lead type. A twelve-lead ECG allows the physician to explore the performance of the heart from twelve different orientations, or angles, so that much more of the heart mass can be evaluated. Ten electrodes are placed on the body as follows: one on the right leg, which serves as the ground electrode; one on each of the other extremities; and six on the precordium, which is the area around the sternum and on the left chest wall (over the heart). The leads are explored in different combinations.
Uses and Complications
Healthy people, including athletes or certain members of the armed services, may take stress tests in order to have their health and cardiovascular conditioning monitored during training. Some professionals are required to take stress tests on a regular basis, such as commercial airline pilots and astronauts. In addition, people who have a family history of cardiovascular disease, or who are concerned about their heart health for other reasons, may have a stress test performed to find early warning signs and allow intervention before a crisis occurs. Finally, it should be noted that some insurance companies require stress tests of their applicants in order to determine insurability before issuing or rejecting a policy.
Treatment for chest pain
is highly dependent on the electrical patterns seen on the ECG. Drugs may be administered or withheld depending on the shape or duration reported for the P-wave, QRS-complex, and T-wave patterns. Left-sided versus right-sided heart disease can be discerned from the traces, and infarction (heart attack) can be distinguished from angina. Although the waves in the electrocardiogram for an infarcted or anginal heart are abnormal, the patterns become abnormal in a predictable, and therefore diagnostic, manner.
Diagnostic patterns can also be seen for arrhythmias (unusual and abnormal beating patterns), such as ectopic foci, in which some part of the heart other than the sinoatrial (S-A) node (the natural pacemaker) is abnormally in control of determining when the heart contracts, or heart block, whereby electrical conduction is interrupted.
ECG is routinely used to keep close tabs on heart patients and in the postsurgery monitoring of patients who have had open heart or thoracic
surgery. Certain kinds of neonatal or infant malformations or malfunctions may also be evaluated with ECG.
Because ECG is a superficial and noninvasive technique, there are no real risks associated with having this procedure performed.
Perspective and Prospects
Electrocardiography was once a wet, messy, and awkward procedure to perform: A patient dangled one arm in a huge jar filled with a conducting salt solution and placed the left leg in another saline-filled container. Changing the leads to include other limbs required the patient to take a good amount of soaking. Although it was a clumsy procedure, the basic premise of ECG remains unchanged: the heart exhibits regular patterns of electrical activity that can be useful diagnostically.
Advances in electrocardiography have involved the use of multiple electrode systems along with computers and recorders that allow rapid and simultaneous multiple-lead input and output. In addition, modern electronic instrumentation allows continuous ECG monitoring so that patients in intensive care units, coronary care units, or emergency rooms can be assessed on a second-by-second basis when seconds count. Undoubtedly, modern ECG systems, coupled with thoughtful and informed interpretation by medical doctors and emergency medical technicians (EMTs), save many lives.
Bibliography
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Conover, Mary Boudreau. Understanding Electrocardiography. 8th ed. St. Louis, Mo.: Mosby, 2003.
Dugdale, David C. III, and David Zieve. "Electrocardiogram." MedlinePlus, June 3, 2012.
"Electrocardiogram." National Heart, Lung, and Blood Institute, Oct. 1, 2010.
Phibbs, Brendan. The Human Heart: A Complete Text on Function and Disease. 5th ed. St. Louis, Mo.: G. W. Manning, 1992.
Scholten, Amy, Michael J. Fucci, and Brian Randall. "Electrocardiogram." Health Library, May 20, 2013.
Surawicz, Borys, and Timothy K. Knilans. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric. 6th ed. Philadelphia: Saunders/Elsevier, 2008.
Thaler, Malcom S. The Only EKG Book You’ll Ever Need. 7th ed. Philadelphia: Lippincott Williams & Wilkins, 2012.
Wellens, Hein J. J., and Mary Conover. The ECG in Emergency Decision Making. 2d ed. St. Louis, Mo.: Saunders/Elsevier, 2006.
Wiederhold, Richard. Electrocardiography: The Monitoring and Diagnostic Leads. 2d ed. Philadelphia: W. B. Saunders, 1999.
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