In medicine, a Holter monitor is a type of ambulatory electrocardiography device, a portable device for cardiac monitoring (the monitoring of the electrical activity of the cardiovascular system) for at least 24 to 48 hours (often for two weeks at a time).
The Holter's most common use is for monitoring ECG heart activity (electrocardiography or ECG). Its extended recording period is sometimes useful for observing occasional cardiac arrhythmias which would be difficult to identify in a shorter period. For patients having more transient symptoms, a cardiac event monitor which can be worn for a month or more can be used.
When used to study the heart, much like standard electrocardiography, the Holter monitor records electrical signals from the heart via a series of electrodes attached to the chest. Electrodes are placed over bones to minimize artifacts from muscular activity. The number and position of electrodes varies by model, but most Holter monitors employ between three and eight. These electrodes are connected to a small piece of equipment that is attached to the patient's belt or hung around the neck, keeping a log of the heart's electrical activity throughout the recording period. A 12 lead Holter system is also available when precise ECG signal information is required to analyse the exact nature and origin of the rhythm signal.
The size of the recorder differs depending on the manufacturer of the device. The average dimensions of today’s Holter monitors are about 110x70x30 mm but some are only 61x46x20 mm and weigh 99 g.  Most of the devices operate with two AA batteries. In case the batteries are depleted, some Holters allow their replacement even during monitoring.
Most of the Holters monitor the ECG via only two or three channels (Note: depending on manufacturer, different counts of leads and lead systems are used). Today’s trend is to minimize the number of leads to ensure the patient’s comfort during recording. Although two/three channel recording has been used for a long time in the Holter monitoring history, as mentioned above, 12 channel Holters have recently appeared. These systems use the classic Mason-Likar lead system, i.e. producing a signal in the same format as during the common rest ECG and/or stress test measurement. These Holters can occasionally provide information similar to that of a ECG stress test examination. They are also suitable when analyzing patients after myocardial infarction. Recordings from these 12-lead monitors are of a significantly lower resolution than those from a standard 12-lead ECG and in some cases have been shown to provide misleading ST segment representation, even though some devices allow setting the sampling frequency up to 1000 Hz for special-purpose exams such as detection of "late potential".
Another innovation is the inclusion of a triaxial movement sensor, which records the patient's physical activity, and on examination and software processing, extracts three movement statuses: sleeping, standing up, or walking. Some modern devices also have the ability to record a vocal patient diary entry that can be later listened to by the doctor. These data help the cardiologist to better identify events in relation to the patient's activity and diary.
Previous: No Information