What are Holter monitors and event Holters?

Holter monitors and event recorders are used for monitoring electrical activity of the heart for a prolonged period of time in order to search for evidence of cardiac problems. However, Holter monitors and event recorders have to be distinguished, since Holter monitors operate only for a few days, while event recorders are able to record electrocardiographic data over a much longer period of time, even for weeks (such as the CardioClip device). The usage method of the two recorders is technically the same. Most frequently 7-lead ECG electrodes, which makes up to 3 independent bipolar or 5 independent unipolar channels, are applied to the patient's skin and connected with a portable device which records ECG signals for a preprogrammed time interval.


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During the monitoring period the patient carries the device in a pocket or in a small pouch and she/he has to keep a diary of activities and signal any important events by pressing a small button on the surface of the device. The patient has to do so whenever she/he takes medication, feels dizzines or palpitation or any suspected cardiac event. When the monitoring period ends, the device is removed, recorded data are processed and measurements are evaluated with the aid of a software programme. It is important to note that both Holters and event recorders and the evaluation software only ensure data to support diagnostic decisions of a qualified physician and they don't provide final diagnosis of any kind.

Event Holters

While Holter monitors record continuous beat-by-beat ECG usually for 24 or 48 hours, event recorders store only sequential ECG strips. It means that unlike Holter monitors, they don't continuously record the electrical activity of the heart only if it have been preset in the software for a certain time interval and length or if the patient starts a measurement when the symptom occurs. Therefore event recorders are able to monitor a longer period of time in order to make the identification of those heart rhythm problems possible that may not occur frequently.


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Consequently, the use of the event recorders is an excellent way to correlate symptoms with the heart rhythm. In contrast, Holter monitors record shorter period of time but provide full disclosure ECG analysis. Therefore Holter monitors are able to detect the more detailed background of possible cardiac diseases even in those cases when no symptoms occur. Such a case is for example silent ischemia. In this condition, the oxygen content of the blood which reaches the heart is not satisfying. The word 'silent' relates to the fact that this phenomenon is not symptomatic. Other major indicatons for the use of Holter monitors are as follows:

- palpitations
- syncope
- pre-syncope
- dizzines
- pacemaker evaluation
- arrhythmia
- brady/tachy disrhythmias


Holter monitors are applied if the symptom is episodic, so it appears and disappears without warning or the symptom occurs almost daily. However, Holter monitors very often don't contribute to support the appropriate diagnostic decisions of the physician, especially if the symptom appears outside of the 24- or 48-hour monitoring period.