An event monitor, also called an ambulatory electrocardiographic monitor, is a battery powered, portable medical device that monitors cardiac activity as a patient goes about an ordinary day. The main purpose of an event monitor is to determine the cause of a transient event by recording a patient’s heart rate and rhythm during a period of time.

In contrast to an EKG, which captures cardiac activity at one point in time, or a Holter monitor, which continuously records over a period of 24-48 hours, an event monitor records intermittently for a period of a few weeks, typically up to 30 days. It is typically prescribed because a prior method of monitoring failed to obtain necessary data, likely because the patient’s symptoms are unpredictable or infrequent, generally occurring less than daily. An event monitor allows for longer monitoring time and a greater chance of capturing an irregularity.

Types of event monitors

Event monitors typically include wired sensors that are attached to the patient’s chest which are then connected to a small recording device. There are two types of event monitors:

• A looping memory monitor, the most common type of event monitor, can be programmed to record ECG activity for a given period of time. When the patient experiences symptoms, he pushes a button to activate the device, which triggers the monitor to record the 60 seconds prior to the event, the event, and up to 40 seconds following.

• A post-event monitor is typically a handheld device or one that can be worn on the patient’s wrist, similar to a bracelet. The small metal discs that are located on the back of the device function as electrodes When the patient experiences symptoms, the monitor is placed on the chest and the patient activates the recording button. This records the current ECG activity. Unlike the looping memory monitor, however, a symptom event monitor will not store any ECG activity that occurs in the minutes prior to its activation.

Both devices are able to send the ECG by telephone to a receiving center or a doctor’s office for review. Any emergency treatment, further testing or monitoring will be addressed as needed.