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What Are Holter and Event Monitors?

Holter and event monitors are medical devices that record the heart's electrical activity. Doctors most often use these monitors to diagnose arrhythmias (ah-RITH-me-ahs).

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 (is-KE-me-ah). In this condition, not enough oxygen-rich blood reaches the heart muscle. "Silent" means that no symptoms occur.

The monitors also can check whether treatments for an arrhythmia or silent myocardial ischemia are working.

This article focuses on using Holter and event monitors to diagnose problems with the heart's rate or rhythm.

Overview

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 a common test for diagnosing heart rhythm problems.

However, a standard EKG only records the heartbeat for a few seconds. It won't detect heart rhythm problems that don't occur during the test.

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.

Some people have heart rhythm problems that occur only during certain activities, such as sleeping or physical exertion. Using a Holter or event monitor increases the chance of recording these problems.

Although similar, Holter and event monitors aren't the same. A Holter monitor records your heart's electrical activity the entire time you're wearing it. An event monitor records your heart's electrical activity only at certain times while you're wearing it.




Types of Holter and Event Monitors

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.

Wireless Holter Monitors

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

These monitors use wireless cellular technology to send the recorded data to your doctor's office or a company that checks the data. The device sends the data automatically at certain times. Wireless monitors still have wires that connect the device to the sensors on 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 1–2 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. 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.

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 monitors 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.

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 might be hard to start the monitor when a symptom is in progress.

In some cases, the missing data could 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 data from before, during, and after the symptom. This may make it possible for your doctor to see very brief changes in your heart 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.

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.



Who Needs a Holter or Event Monitor?

Your doctor may recommend a Holter or event monitor if he or she thinks you have an arrhythmia. An arrhythmia is a problem with the rate or rhythm of the heartbeat.

Holter and event monitors most often are used to detect arrhythmias in people who have:

  • Issues with fainting or feeling dizzy. A monitor might be used if causes other than a heart rhythm problem have been ruled out.
  • Palpitations (pal-pih-TA-shuns) that recur with no known cause. Palpitations are feelings that your heart is skipping a beat, fluttering, or beating too hard or fast. You may have these feelings in your chest, throat, or neck.

People who are being treated for heart rhythm problems also may need to use Holter or event monitors. The monitors can show how well their treatments are working.

Heart rhythm problems may occur only during certain activities, such sleeping or physical exertion. Holter and event monitors record your heart rhythm while you do your normal daily routine. This allows your doctor to see how your heart responds to various activities.




What To 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 may:

  • Check your pulse to find out how fast your heart is beating (your heart rate) and whether your heart rhythm is steady or irregular.
  • Measure your blood pressure.
  • Check for swelling in your legs or feet. Swelling could be a sign of an enlarged heart or heart failure, which may cause an arrhythmia. An arrhythmia is a problem with the rate or rhythm of the heartbeat.
  • Look for signs of other diseases that might cause heart rhythm problems, such as thyroid disease.

You may have an EKG (electrocardiogram) test before your doctor sends you home with a Holter or event monitor.

An EKG is a simple test that records your heart's electrical activity for a few seconds. The test shows how fast your heart is beating and its rhythm (steady or irregular). An EKG also records the strength and timing of electrical signals as they pass through your 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'll leave the office wearing it.

Each type of monitor is slightly different, but most have sensors (called electrodes) that attach to the skin on your chest using sticky patches. The sensors need good contact with your skin. Poor contact can cause 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 the patches. If you have to replace the patches, you'll 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 help the patches stick to your skin. Some patches come with paste or gel on them.




What To 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. Thus, maintaining a clear signal between the sensors (electrodes) and the recording device is important.

In most cases, the sensors are attached to your chest using 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 recorders and implantable loop recorders don't have chest sensors.)

Holter or Event 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.

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.

A good stick between the patches and your skin helps provide a clear signal. Poor contact leads to a poor recording that's 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 the patches. If you have to replace the patches, you'll need to clean the area with a special prep pad that your doctor will provide.

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

Too much movement can pull the patches away from your skin or create "noise" on the EKG (electrocardiogram) strip. An EKG strip is a graph showing the pattern of the heartbeat. Noise looks like a lot of jagged lines; it makes it hard for your doctor to see the real rhythm of your heart.

When you have a symptom, stop what you're doing. This will ensure that the recording shows your 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 MP3 players (such as iPods) may interfere with the signal between the sensors and the monitor 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

While using a Holter or event monitor, your doctor will advise you to keep a diary of your symptoms and activities. Write down what type of symptoms you're having, when they occur, and what you were doing at the time.

The most common symptoms of heart rhythm problems include:

  • Fainting or feeling dizzy.
  • Palpitations. These are feelings that your heart is skipping a beat, fluttering, or beating too hard or fast. You may have these feelings in your chest, throat, or neck.

Make sure to note the time that symptoms occur, because your doctor will match 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.

Also, include details in your diary about when you take any medicine or if you feel stress at certain times during the testing period.

What To Expect With Specific Monitors

Holter Monitors

Holter monitors are about the size of a large deck of cards. You'll wear one for 24 to 48 hours. You can't get your monitor wet, so you won't be able to bathe or shower. You can take a sponge bath if needed.

When the testing period is done, you'll return the device to your doctor's office. The results will be stored on the device.

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

Wireless Holter Monitors

Wireless Holter monitors can record for a longer time than standard Holter monitors. You can use a wireless Holter monitor for days or even weeks, until signs or symptoms of a heart rhythm problem occur.

Wireless monitors record for a preset amount of time. Then they automatically send data to your doctor's office or a company that checks the data.

These monitors use wireless cellular technology to send data. However, they still have wires that connect the device to the sensors stuck to your chest.

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

Event Monitors

Event monitors are slightly smaller than Holter monitors. 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 on your monitor to start recording. Some event monitors start automatically if they detect abnormal heart rhythms.

Postevent Recorders

Postevent recorders can 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 his or her 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 if it detects abnormal heart rhythms. 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. Your doctor will discuss the procedure with you. No chest sensors are used with implantable loop recorders.

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 device to start it.




What To Expect After Using a Holter or Event Monitor

After you're finished using a Holter or event monitor, you'll return it to your doctor's office or the place where you picked it up.

If you were using an implantable loop recorder, your doctor will need to remove it from your chest. He or she 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 or Event Monitor Show?

A Holter or event monitor may show what's causing symptoms of an arrhythmia. An arrhythmia is a problem with the rate or rhythm of the heartbeat.

A Holter or event monitor also can show whether a heart rhythm problem is harmless or requires treatment. The monitor might alert your doctor to medical conditions that can result in heart failure, stroke, or sudden cardiac arrest.

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

Sometimes Holter and event monitors can't help doctors diagnose heart rhythm problems. If this happens, talk with your doctor about other steps you can take.

One option might be to try a different type of monitor. Wireless Holter monitors and implantable loop recorders have longer recording periods. This may allow your doctor to get the data he or she needs to make a diagnosis.




What Are the Risks of 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 to 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. Your doctor can prescribe medicine to treat these problems.




Links to Other Information About Holter and Event Monitors

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March 16, 2012 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.