An event monitor is typically used by a patient for 7 - 15 days, depending on the frequency of the symptoms. When the patient has symptoms, he/she activates the device by pressing a button on it to signal 'an event'. The heart rhythm prior to and during the event is stored in the device memory. This technology is useful for the examination of patients who have intermittent or rare symptoms, since the device can be used for long periods of time. As the event monitor has 'memory' prior to activation, they are excellent for documenting transient events. The information stored in the device can be sent by the patient by telephone transmission directly to a receiving station, making the ECG recordings available for review by a cardiologist.
The technologies of ambulatory ECG (Holter monitor) and event monitor with trans-telephonic transmission of ECG data are complementary. As an example, current evidence indicates that event monitors are the examination of choice in patients with recurrent or unexplained syncope (fainting) that remain undiagnosed despite clinical examination and ambulatory ECG monitoring.