Holter Monitors

Holter monitors sometimes are called continuous EKGs (electrocardiograms). This is because Holter monitors record your heart rhythm continuously for 24 to 48 hours.

A Holter monitor is about the size of a large deck of cards. You can clip it to a belt or carry it in a pocket. Wires connect the device to sensors (called electrodes) that are stuck to your chest using sticky patches. These sensors detect your heart’s electrical signals, and the monitor records your heart rhythm.

Event Monitors

Event monitors are similar to Holter monitors. You wear one while you do your normal daily activities. Most event monitors have wires that connect the device to sensors. The sensors are stuck to your chest using sticky patches.

Unlike Holter monitors, event monitors don’t continuously record your heart’s electrical activity. They only record during symptoms. For many event monitors, you need to start the device when you feel symptoms. Some event monitors start automatically if they detect abnormal heart rhythms.

Event monitors tend to be smaller than Holter monitors because they don’t need to store as much data.

Different types of event monitors work in slightly different ways. Your doctor will explain how to use the monitor before you start wearing it.

Implantable Loop Recorders

You may need an implantable loop recorder if other event monitors can’t provide enough data. Implantable loop recorders are about the size of a pack of gum. This type of event monitor is inserted under the skin on your chest. No wires or chest sensors are used.

Your doctor can program the device to record when you start it during symptoms or automatically if it detects an abnormal heart rhythm. Devices may differ, so your doctor will tell you how to use your recorder. Sometimes a special card is held close to the recorder to start it.

Other Names for Holter and Event Monitors

  • Ambulatory EKG or ECG. (The terms “EKG” and “ECG” both stand for electrocardiogram.)
  • Continuous EKG or ECG.
  • EKG event monitors.
  • Episodic monitors.
  • Mobile cardiac outpatient telemetry systems. This is another name for autodetect recorders.
  • Thirty-day event recorders.
  • Transtelephonic event monitors. These monitors require the patient to send the collected data by telephone to a doctor’s office or a company that checks the data.


Source: National Heart, Lung, and Blood Institute; National Institutes of Health; U.S. Department of Health and Human Services.