South Bay Cardiovascular Center

Heart Arrhythmia

Holter Monitor and Event Monitors

  • Holter monitors and event monitors are medical devices that record the heart's electrical activity.
Holter Monitor

Figure A shows how a Holter or event monitor attaches to a patient. In this example, the monitor is clipped to the patient’s belt and electrodes are attached to his chest. Figure B shows an electrocardiogram strip, which maps the data from the Holter or event monitor.

  • Doctors most often use these monitors to diagnose heart arrhythmias. Arrhythmias are problems with the rate or rhythm of the heartbeat. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm.
  • Holter and event monitors also are used to detect silent myocardial ischemia. In this condition, not enough oxygen-rich blood reaches the heart muscle. "Silent" means that no symptoms occur.
  • Holter and event monitors are similar to an EKG (electrocardiogram). An EKG is a simple test that detects and records the heart's electrical activity. It's the most common test for diagnosing a heart rhythm problem. However, a standard EKG only records the heartbeat for a few seconds.
  • Holter and event monitors are small, portable devices. You can wear one while you do your normal daily activities. This allows the monitor to record your heart for a longer time than an EKG. Holter and event monitors are used to detect heart rhythm problems that may not occur all the time.
  • People who are being treated for a heart rhythm problem also may need to use a Holter or event monitor. The monitors can show how treatment is working.
  • After you're finished using a Holter or event monitor, you return it to your doctor's office or the place where you picked it up. Your doctor will tell you when to expect the results.
  • A Holter or event monitor may show what's causing symptoms of a heart rhythm problem. The monitor also can show whether a heart rhythm problem is harmless or requires treatment. The monitor may alert your doctor to medical conditions that can result in heart failure, stroke, or sudden cardiac arrest.

What are the different types of heart monitors?

Holter monitors

Holter monitors are sometimes called continuous EKGs (electrocardiograms). This is because Holter monitors record the 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 pick up your heart's electrical signals, and the monitor records your heart's rhythm.

Wireless holter monitors

Wireless Holter monitors have a longer recording time than standard Holter monitors. The wireless version records your heart's electrical activity for a preset amount of time.

These monitors are called wireless because they use a cell phone to send the data to your doctor's office. This happens automatically at certain times. These monitors still have wires that connect the device to the sensors stuck to your chest.

You can use a wireless Holter monitor for days or even weeks until signs or symptoms of a heart rhythm problem occur. These monitors usually are used to detect heart rhythm problems that don't occur often.

Although wireless Holter monitors work for longer periods, they have a down side. You must remember to write down the time of symptoms, so your doctor can match it to the heart rhythm recording. Also, the batteries in the wireless monitor must be changed every 1 to 2 days.

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 that are stuck to your chest using sticky patches.

Unlike Holter monitors though, event monitors don't continuously record the heart's electrical activity. They only record when symptoms occur. For many event monitors, you need to start the monitor when you feel symptoms.

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.

Postevent recorders

Postevent recorders are among the smallest event monitors. You can wear a postevent recorder like a wristwatch or carry it in your pocket. The pocket version is about the size of a thick credit card. These recorders don't have wires that connect the device to chest sensors.

When you feel a symptom, you start the recorder. A postevent recorder only records what happens after you start it. It may miss a heart rhythm problem that occurs before and during the onset of symptoms. Also, it may be hard to start the monitor when a symptom is in progress.

In some cases, this missing data would have helped your doctor diagnose the heart rhythm problem.

Presymptom memory loop recorders

Presymptom memory loop recorders are the size of a small cell phone. They're also called continuous loop event recorders.

You can clip this event monitor to your belt or carry it in your pocket. Wires connect the device to sensors on your chest.

These recorders are always recording and erasing data. When you feel a symptom, you push a button on the device. The normal erase process stops. The recording will show a few minutes of the data from before, during, and after the symptom.

In some cases, this makes it possible for your doctor to see very brief changes in your heart's rhythm.

Autodetect recorders

Autodetect recorders are about the size of the palm of your hand. Wires connect the device to sensors on your chest.

You don't need to start an autodetect recorder during symptoms. These recorders detect abnormal heart rhythms and automatically record and send the data to your doctor's office.

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.

The device records either when you activate it or automatically when symptoms occur. It depends on how your doctor programs it. Devices may differ, so your doctor will tell you how to use it. In some cases, a special card is held close to the recorder to start it.

Who needs a Holter or event monitor?

You may need a Holter or event monitor if your doctor suspects you have an arrhythmia. This is a problem with the speed or rhythm of your heartbeat. Holter or event monitors are most often used to detect arrhythmias in people who have:

  • Fainted or sometimes feel dizzy. A monitor may be used if causes other than a heart rhythm problem have been ruled out.
  • Palpitations that recur with no known cause. Palpitations are the feeling that your heart is pounding, racing, fluttering, or beating unevenly.

People who are being treated for a heart rhythm problem also may need to use a Holter or event monitor. These monitors can show how treatment is working.

In some people, heart rhythm problems only occur during certain events, such as sleep or physical exertion. Holter and event monitors record the heart rhythm while a person does his or her normal daily routine. This allows the doctor to see how the heart responds to different daily activities, which helps diagnose the problem.

Holter and event monitors also are used for elderly people who may have trouble getting to and from clinics.

What should I expect before using a Holter or event monitor?

Your doctor will do a physical exam before giving you a Holter or event monitor. He or she will:

  • Check your pulse to find out how fast your heart is beating and measure your blood pressure.
  • Listen to the rate and rhythm of your heart.
  • Check for swelling in your legs or feet. This could be a sign of an enlarged heart or heart failure, which may cause arrhythmias (problems with the speed or rhythm of the heartbeat).
  • Look for signs of other diseases (such as thyroid disease) that could be causing heart rhythm problems.

You may have an EKG (electrocardiogram) test before your doctor sends you home with a Holter or event monitor. An EKG detects and records the electrical activity of the heart for a few seconds. It shows how fast the heart is beating and its rhythm (steady or irregular). It also records the strength and timing of electrical signals as they pass through each part of the heart.

A standard EKG won’t detect heart rhythm problems that don’t happen during the test. For this reason, your doctor may give you a Holter or event monitor. These monitors are portable. You can wear one while doing your normal daily activities. This increases the chance of recording symptoms that only occur once in a while.

Your doctor will explain how to wear and use the Holter or event monitor. Usually, you will leave the office wearing it.

Each type of monitor is slightly different, but most have sensors (called electrodes) that are attached to the skin on your chest with sticky patches. It’s important that the sensors have good contact with your skin. Poor contact can result in poor results.

Oil, too much sweat, and hair can keep the patches from sticking to your skin. You may need to shave the area on your chest where your doctor will attach each patch. You will need to clean the area with a special prep pad that the doctor will provide.

You may need to use a small amount of special paste or gel to make the patches stick to your skin better. Some patches come with paste or gel on them.

What should I expect while using a Holter or event monitor?

Your experience while using a Holter or event monitor depends on the type of monitor you have. However, most monitors have some factors in common.

Recording the heart’s electrical activity

All monitors record the heart’s electrical activity. So, it’s important to maintain a clear signal between the sensors (electrodes) and the recording device.

In most cases, the sensors are attached to your chest with sticky patches. Wires connect the sensors to the monitor. You usually can clip the monitor to your belt or carry it in your pocket. (Postevent and implantable loop recorders don’t have chest sensors.)

A good stick between the patches and your skin helps provide a clear signal. Poor contact leads to a poor recording, which is hard for your doctor to read.

Oil, too much sweat, and hair can keep the patches from sticking to your skin. You may need to shave the area where your doctor will attach each patch. You will need to clean the area with a special prep pad that your doctor provides.

You may need to use a small amount of special paste or gel to make the patches stick to your skin better. Some patches come with paste or gel on them.

Too much movement can pull the patches away from the skin or create “noise” on the rhythm strip. A rhythm strip is a graph showing the pattern of the heartbeat. Noise looks like a lot of jagged lines and makes it hard for the doctor to see the real rhythm of the heart.

When you have a symptom, stop what you’re doing. This way you can be sure that the recording shows the heart’s activity rather than your movement.

Your doctor will tell you whether you need to adjust your activity level during the testing period. If you exercise, choose a cool location to avoid sweating too much. This will help the patches stay sticky.

Other everyday items also can disrupt the signal between the sensors and the monitor. These items include magnets, metal detectors, microwave ovens, and electric blankets, toothbrushes, and razors. Avoid using these items. Also avoid areas with high voltage.

Cell phones and iPods may interfere with the signal if they’re too close to the monitor. When using any electronic device, try to keep it at least 6 inches away from the monitor.

Keeping a diary

When using a Holter or event monitor, you need to keep a diary of your symptoms and activities. Write down when symptoms occur, what they are, and what you were doing at the time.

The most common symptoms of heart rhythm problems include:

  • Palpitations. This is the feeling that your heart is pounding, racing, fluttering, or beating unevenly.
  • Fainting or feeling dizzy.

It’s important to note the time symptoms occur, because your doctor matches the data with the information in your diary. This allows your doctor to see whether certain activities trigger changes in your heart rate and rhythm.

You also should include details in your diary about when you take any medicine or if you feel stress at certain times during the test.

What to expect with specific monitors

Holter monitor

The Holter monitor is about the size of a large deck of cards. You wear it for 24 to 48 hours. When the test is complete, you return the device to your doctor’s office. The results are stored on the device.

You can’t get the monitor wet, so you won’t be able to bathe or shower. You can take a sponge bath if needed.

The recording period for a standard Holter monitor may be too short to capture a heart rhythm problem. If this is the case, you may need a wireless Holter monitor.

Wireless Holter monitors

Wireless Holter monitors can record for a longer time than standard Holter monitors. A wireless monitor records for a preset amount of time. It then automatically sends data from the monitor to your doctor’s office.

These monitors are called wireless because they use a cell phone to send the data to your doctor’s office. They still have wires that connect the device to the sensors stuck to your chest.

You can use a wireless Holter monitor for days or even weeks until signs or symptoms of a heart rhythm problem occur.

The batteries in the wireless monitor must be changed every 1 to 2 days. You will need to detach the sensors to shower or bathe and then reattach them.

Event monitors

Event monitors are slightly smaller than Holter monitors. Event monitors record heart rhythm problems when you activate them. They can be worn for weeks or until symptoms occur.

Most event monitors are worn like Holter monitors—clipped to a belt or carried in a pocket. When you have symptoms, you simply push a button to start recording.

Postevent recorders

Postevent recorders may be worn like a wristwatch or carried in a pocket. The pocket version is about the size of a thick credit card. These recorders don’t have wires that connect the device to chest sensors.

To start the recorder when you feel a symptom, you hold it to your chest. To start the wristwatch version, you touch a button on the side of the watch.

You send the stored data to your doctor’s office using a telephone. Your doctor will explain how to use the monitor before you leave the office.

Autodetect recorders

Autodetect recorders are about the size of the palm of your hand. Wires connect the device to sensors on your chest.

You don’t need to start an autodetect recorder. This type of monitor automatically starts recording when it detects an abnormal heart rhythm. It then sends the data to your doctor’s office.

Implantable loop recorders

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 chest sensors are used.

The device records either when you activate it or automatically when symptoms occur. It depends on how your doctor programs it. Devices may differ, so your doctor will tell you how to use it. In some cases, a special card is held close to the recorder to start it.

What should I expect after using a Holter or event monitor?

After you’re finished using a Holter or event monitor, you return it to your doctor’s office or the place you got it from.

If you were using an implantable loop recorder, you will need to have it removed. Your doctor will discuss the procedure with you.

Your doctor will tell you when to expect the results. Once your doctor has reviewed the recordings, he or she will discuss the results with you.

What does a Holter monitor or event monitor show?

A Holter or event monitor may show what’s causing symptoms of an arrhythmia. This is problem with the speed or rhythm of the heartbeat.

Holter and event monitors also can show whether a heart rhythm problem is harmless or whether it needs treatment. Treatment is needed if the problem causes serious symptoms or increases your chance for complications.

Serious symptoms may include dizziness, chest pain, and fainting. Complications may include heart failure, stroke, or sudden cardiac arrest.

If the symptoms of your heart rhythm problem occur often, a Holter or event monitor has a good chance of capturing them. You may not have symptoms while using a monitor. Even so, your doctor may learn more about your heart rhythm from the test results.

Sometimes, these monitors can’t help doctors diagnose heart rhythm problems. If this happens, talk to your doctor about other steps you can take.

One option may be to try a different type of monitor. The wireless Holter monitor and the implantable loop recorder have longer recording periods. This may allow the monitor to get the data that your doctor needs to make a diagnosis.

What are the risks from using a Holter or event monitor?

The sticky patches used to attach the sensors (electrodes) to your chest have a small risk of skin irritation. You also may have an allergic reaction the paste or gel that’s sometimes used to attach the patches. The irritation will go away once the patches are removed.

If you’re using an implantable loop recorder, you may get an infection or have pain where the device is placed under the skin. You may be given medicine to treat these complications.


Reference: The National Heart, Blood, and Lung Institute.

Last updated May 1, 2017