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Continuous Ambulatory Electrocardiography

By Michael J. Shea, MD, Professor of Internal Medicine, Michigan Medicine at the University of Michigan

(See also Electrocardiography.)

Abnormal heart rhythms and inadequate blood flow to the heart muscle may occur only briefly or unpredictably. To detect such problems, doctors may use continuous ambulatory electrocardiography (ECG), in which the ECG is recorded continuously for 24 to 48 hours while the person engages in normal daily activities.

A Holter monitor is a small monitor that is attached to a strap that the person wears over the shoulder. Electrodes are attached to the person's chest and record the activity of the heart. This type of monitor is painless and is worn for 24 to 48 hours.

Holter Monitor: Continuous ECG Readings

The small monitor is attached to a strap worn over one shoulder. Through electrodes attached to the chest, the monitor continuously records the electrical activity of the heart.

An event monitor is used when a person must be monitored longer than 24 hours. It is similar to a Holter monitor, but it records only when the user activates it—that is, when symptoms occur—by pressing a button on the device. If symptoms occur so rarely that they cannot be captured during 24-hour monitoring, an event monitor may be placed under the skin for up to a year. A small magnet is used to activate this monitor.

How continuous ambulatory electrocardiography is done

For this procedure, the person wears a small battery-powered device (Holter monitor) held on with a shoulder strap. The monitor detects the heart's electrical activity through electrodes attached to the chest and records the ECG. While wearing the monitor, the person notes in a diary the time and type of any symptoms. Subsequently, the ECG is run through a computer, which analyzes the rate and rhythm of the heart, looks for changes in electrical activity that could indicate inadequate blood flow to the heart muscle, and produces a record of every heartbeat during the 24 hours. Symptoms recorded in the diary can then be checked against any changes in the ECG to determine whether an arrhythmia is the cause of the symptoms.

If necessary, the ECG can be transmitted by telephone to a computer at the hospital or doctor's office for an immediate reading as soon as symptoms occur.

A newer option to continuously record the ECG is a small (2 inch by 5 inch) disposable wireless adhesive monitor that is worn on the chest for up to 2 weeks. Because it is much smaller than a Holter monitor and does not require the multiple wire leads to be placed on the chest, people may find it easier to wear for longer periods of time. However, the device is more expensive than a Holter monitor or an event monitor.

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