Holter monitor

In medicine, a Holter monitor (also called an ambulatory electrocardiography device), named after its inventor, Dr. Norman J. Holter, is a portable device for continuously monitoring the electrical activity of the heart for 24 hours or more. Its extended recording period is sometimes useful for observing occasional cardiac arrhythmias that would be difficult to identify in a shorter period of time. For patients having more transient symptoms, a cardiac event monitor which can be worn for a month or more can be used.

Much like standard electrocardiography (ECG), the Holter monitor records electrical signals from the heart via a series of electrodes attached to the chest. The number and position of electrodes varies by model, but most Holter monitors employ from three to eight. These electrodes are connected to a small piece of equipment that is attached to the patient's belt, and is responsible for keeping a log of the heart's electrical activity throughout the recording period.

Old devices used to use reel to reel or a standard C120 audio cassette and ran at a 2mm/second to record the data. Once the recording has been made, it is played back and analysed at 60x the speed so 24 hours of recording can be analysed in 24 minutes. More modern units record onto digital flash memory devices. The data are uploaded into a computer which then automatically analyzes the input, counting ECG complexes, calculating summary statistics such as average heart rate, minimum and maximum heart rate, and finding candidate areas in the recording worthy of further study by the technician.

Electrodes should be placed over bones to minimize artifacts from muscular activity.

Both 24h and 30 day event recorders are available.

Event diary

In addition to wearing the device, most patients are asked to keep a diary of activities such as running and sleeping, symptoms, and times that their symptoms occur. This information is used by doctors and technicians to rapidly pinpoint problem areas in the vast amount of data recorded during the monitoring period.


Wearing the monitor

The recording device can be worn on a belt or in a case on a strap worn across the chest. Individuals who want to minimize the visibility of the device can wear layers or bulky clothes so the case is not as obvious. Also, because of the placement of the electrodes, individuals wearing a holter monitor may wish to wear shirts with a high neck.

Generally, the monitors cannot be worn in the shower.


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