Ambulatory electrocardiography (ECG or EKG) is the continuous monitoring on an outpatient basis of the electrical activity of the heart, with a device called a Holter monitor, while the patient undergoes their usual daily activities.
Ambulatory EKG has the ability to detect a number of heart problems that do not show up during standard electrocardiography tests in a doctor's office or during a stress test (electrocardiography performed during exercise, also in a doctor's office or EKG laboratory). It is commonly used in the evaluation of palpitations (unpleasant awareness of the heartbeats) or syncope (fainting) or to detect electrical symptoms of cardiac ischemia, a deficiency of oxygen to the heart due to reduced blood flow. This disease is sometimes called "silent" ischemia because there are often no outward symptoms of the oxygen deprivation.
Because ambulatory EKG involves 24 hour monitoring, it is also particularly useful in detecting conditions that occur periodically, such as during sleep or at times of emotional or physical stress. The test can be used to screen for arrhythmias (abnormal heartbeats) and is routinely done in patients after myocardial infarctions that resulted in decreased function of the left ventricle. Ambulatory EKG can also detect transient arrhythmias in patients with idiopathic (unknown cause) dilated cardiomyopathy, hypertrophic cardiomyopathy or congestive heart failure.
The long-term nature of the test makes it useful in evaluating the effectiveness of medications used to control irregular heartbeats or arrhythmia or the effectiveness of other cardiac treatments. Because of the compact nature of the device, this test was used by astronauts on the space shuttle to study how the heart adapts to the weightlessness of space.
There are no particular precautions for this test.
Ambulatory electrocardiography, also called continuous ambulatory electrocardiography or Holter monitoring, involves being attached to a portable recorder for 24 to 48 hours. The electrical signals are generally recorded on a magnetic tape for later review. To begin the test, an electrodiagnostic technician attaches five adhesive electrodes to the skin of the chest. Typically, electrodes are placed under each collarbone and each bottom rib, and several electrodes are placed across the chest in a rough outline of the heart. Wires snap onto each of these electrodes and connect them to a small recorder that looks like a wearable radio. The electrodes detect the heart's electrical pattern throughout the day and will store information in the recording box for doctors to interpret later. A small purse with a shoulder strap is used to hold this recorder or it is placed on a belt around the waist.
During the test, patients perform normal activities except they cannot take showers or baths and should avoid electric blankets while wearing the monitor. Often patients are given a small diary to record their various activities, such as exercise, eating, sleeping, straining, breathing too hard (hyperventilating), and any stressful situations. The patient also notes the time and circumstances of any symptoms—especially chest pain, dizziness, shortness of breath, heart palpitations, and any other signs of heart trouble. Some Holter monitors allow patients to record their symptoms electronically, highlighting the portion of the electrocardiogram recorded while the symptoms are occurring. Additionally, some monitors can also perform electroencephalography (EEG), a measurement of the electrical activity of the brain. These dual monitors can be useful in the diagnosis of unexplained loss of consciousness (syncope).
A device similar to a Holter monitor, called an event or loop recorder, can be used to perform ambulatory EKG when the symptoms are very periodic. Generally, these devices have only two electrodes and are the size of a beeper. The event recorder can continuously monitor the heartbeat, but will permanently store the patient's heartbeat only after the patient has pushed a button that freezes the recording process. The device can only store about 30 seconds to two minutes of signal. The button system does allow physical symptoms to be directly correlated with the electrical signals of the heart during the event. Stored signals can be sent through the telephone to the doctor for analysis.
Additionally, because events often last more than a minute and electrodes can be rapidly positioned, the patient can attach to the machine only when a cardiac event occurs. The continuous monitoring issue is completely avoided with newer devices, such as a credit card-sized monitor that is pressed to the chest wall only when the patient detects symptoms.
Patients are asked not to apply creams or lotions to the chest before the test, as this may inhibit the attachment of the electrodes. Sometimes the chest will be shaved of hair to improve electrode function. Wearing loose, comfortable clothing will also make the monitoring process easier.
The electrodes are removed after the monitoring period is completed and the patient may return to normal activities. Results are generally available a few days after the test is complete.
The only limitations to these monitoring procedures is the need to have recorded the heartbeat during an abnormal event. There are no physical complications that result from the monitoring.
A standard ambulatory EKG will record all the beats of the heart for the period that the device is connected to the patient, while an event recorder will have signals recorded only for a short period after the event button was depressed. Computers are often used as a first stage review the lengthy tapes produced by standard ambulatory EKG testing. The program will highlight abnormal rhythms or abnormal signal shape for closer inspection by the doctor. Some standard monitors are equipped with an event button that highlights electrical output during symptoms. This helps the doctor correlate symptoms with electrical signals, similar to what occurs with a event recorder.
"Silent" ischemia is detected by a change in the shape of the heartbeat signal. In electrocardiography, the five different waves seen in a normal heartbeat are labeled PQRST. Reduced oxygen to the heart often changes the shape of the ST portion of the electrical signal.
If the purpose of the test is screening for arrhythmias, the recording will be reviewed for any atypical electrical patterns. Among the abnormal patterns that can be seen are transient brachycardia (sporadic abnormally slow heartbeats), atrial fibrillation (rapid, unproductive contraction of the atria), atrial tachycardia (abnormally fast beating of the atria), and paryoxsmal supraventricular tachycardia (PSVT), a sporadic fast heartbeat that starts above the ventricles.
If the test is performed to evaluate a treatment, the doctor or technician will scan the record for a return to normal rate and graphic shape of heartbeats.
Health care team roles
Specially trained assistants known as electrocardiograph technicians often prepare patients for ambulatory EKG testing in larger hospital and cardiology group practice settings. In small settings, nurses and medical assistants set up the test. A doctor, often aided by a computer, usually does the final interpretation of the tracing.
Arrhythmia— An abnormal rhythm of the heart, if transient (periodic) it is often diagnosed using ambulatory EKG.
Cardiomyopathy— A disease of the muscle of the heart.
Ischemia— A lack of oxygen to a tissue, cardiac ischemia is often due to clogging of the coronary arteries.
Palpitation— An unpleasant awareness of the heart beating, can also encompass skipped beats or rapid beats.
Syncope— A loss of consciousness, fainting, a condition that can be caused by heart disease.
Many persons learn how to perform ambulatory EKG monitoring through on the job training. However, training programs for EKG work in general, that includes ambulatory techniques, are available through out-sourcing companies or in vocational and community colleges. The usual length of these college-based programs is 465 hours (four months). Program content includes classroom instruction in anatomy and physiology with an emphasis on the cardiac and vascular system, medical terminology, cardiovascular medications, patient care techniques, interpretation of cardiac rhythm, medical ethics, and a clinical practicum.
Topol, Eric J., ed. Cleveland Clinic Heart Book New York: Hyperion, 2000.
Bubien, Rosemary S. "A New Beat on an Old Rhythm." American Journal of Nursing 100 (January 2000).
Sadovsky, Richard. "Ambulatory Arrhythmia Monitoring Devices." American Family Physician (December 1999).
American Heart Association. 7272 Greenville Avenue, Dallas, Texas 75231. (800) AHA-USA1. 〈http://www.americanheart.org〉.