What Is the Holter Monitor Study?

What to expect when undergoing this test

The Holter monitor study is the original, and still most widely used, type of ambulatory electrocardiographic (ECG) monitoring. It is named for Norman J. Holter, the physicist chiefly responsible for its invention in the 1950s. 

As with any type of ambulatory ECG monitoring, the main aim of a Holter monitor study is to analyze the electrical activity of the heart outside of the clinical setting—that is, as a person goes about his or her normal daily activities.

When a person has a Holter monitor study, they wear the monitoring device for either 24 or 48 hours, and the ECG recorded during this time is subsequently analyzed for any cardiac arrhythmias that might have occurred during the monitoring period, as well as for any signs of cardiac ischemia.

The Holter monitor study is very effective in diagnosing cardiac arrhythmias, as long as they occur with sufficient frequency. The test is very safe.

what to expect during a Holter monitor study
Illustration by Cindy Chung, Verywell

Purpose of Test

There are many types of cardiac arrhythmias. They can produce various symptoms, and they differ tremendously in their medical significance and in their treatments. So if a person is suspected to have an arrhythmia, it is important to diagnose the precise nature of the arrhythmia in order to decide what, if anything, needs to be done about it. This means that the arrhythmia has to be captured on an ECG.

However, many cardiac arrhythmias occur only infrequently and completely unpredictably—and are often present for only brief periods of time. The odds of capturing one of these rare or fleeting arrhythmias while a doctor happens to be recording a standard ECG (which records the heart rhythm for only 12 seconds), is quite small.

Furthermore, symptoms caused by arrhythmias may also last for only a short period of time. By the time a person experiencing symptoms can get to a medical facility to have an ECG recorded, all too often the symptoms (and the arrhythmia that caused them) have gone away.

The Holter monitor was developed to address the problem of diagnosing infrequent or fleeting cardiac arrhythmias. By recording each and every heartbeat that occurs over a prolonged period of time, while a person goes about their activities of daily life, the odds of detecting one of these transient arrhythmias are greatly increased.

When Should a Holter Study Be Done?

A Holter monitor study is most often used when a person is having transient episodes of symptoms that might be explained by a heart rhythm disturbance. Most often these symptoms are:

Much less often, Holter monitor studies can also be used to look for episodes of cardiac ischemia that are not producing angina. Because this ischemia is not causing symptoms, it is often referred to as “silent ischemia.” However, the ECG changes caused by ischemia on a Holter study are often quite nonspecific, and such ECG changes can be misleading. So most cardiologists do not often order a Holter study for this purpose, unless they are dealing with a patient who is known to have had silent ischemia—such as a person in whom silent ischemia was diagnosed on a stress test, or who has had a silent heart attack in the past.

So, by far, Holter monitor studies are used most often to diagnose cardiac arrhythmias.

Risks and Contraindications

The Holter monitor study is virtually free of risk, except for a small chance of skin irritation at the site of electrode placement.

A Holter study is not always the best kind of ambulatory ECG monitoring to perform. If there is a good reason to believe that the arrhythmia you’re trying to diagnose is so infrequent that it is unlikely to occur in any given 24-48 hour period, a different type of ambulatory ECG monitoring that can be employed for weeks (or longer) should be considered.

Before the Test

Knowing these details before the test can help ease any fear or anxiety you're experiencing.

Timing

You and your doctor will decide together on a good time to do the test. Almost any 24-48 hour period will typically suffice, but it is best to pick a time when you are not traveling (to avoid hassles at airport security), are not planning water-based activities, or activities that will drench you in sweat (because you need to stay dry while wearing a Holter monitor).

Location

You will need to go to an outpatient facility, usually at a local hospital, to have your Holter monitor attached by a technician. This takes just a few minutes. You may be asked to return to the same facility to have the Holter removed at the end of the test, but many Holter labs now employ delivery services to pick up the recorder from your home when the test is finished.

What to Wear

While you can wear any comfortable clothing, a loose-fitting top is required so that the Holter monitor can be comfortably worn underneath.

Other Preparation

You can eat and drink as you normally would prior to the test, and (unless your doctor tells you otherwise) you can take your normal medication. It is a good idea to bathe before beginning a Holter monitor study, because you will be unable to do so while wearing the monitor.

Cost and Health Insurance

The cost of the study varies. Almost all health insurance covers Holter monitor studies as long as it is ordered by a licensed physician. It is never a bad idea to check with your insurance company ahead of time, however.

During the Test

A Holter monitor consists of several tiny electrode patches that adhere to the skin, and that are attached by small wires to a recording device. The recording device (which used to be a small tape recorder, but today is more often a digital recorder that is no larger than a deck of cards), can be worn around the neck or attached to a belt. The electrodes, wires, and recording device are hidden under your clothes. At the end of the test, the electrodes and wires are removed, and the recording device is returned to the laboratory for analysis.

Pre-Test

When you arrive at the Holter laboratory, a technician will place the electrodes (which are about the size of a 50-cent piece) at appropriate locations on your chest and attach them to the monitor. Men may have to be shaved in small patches in order for the electrodes to adhere properly.

The technician will help you decide how to wear the recording device, instruct you on do’s and don’ts, and will tell you how to keep a diary of your activities and symptoms. You will then be sent on your way.

Throughout the Test

During the test, you will simply follow your normal routine, with two big exceptions. First, you will need to keep the Holter equipment dry—so no showering, and no bathing of the chest area.

Second, you will need to keep a diary of all the activities you perform, and of any symptoms you may experience while wearing the Holter monitor. In particular, your doctor will be most interested in symptoms of lightheadedness, palpitations, syncope, chest pain or shortness of breath. The precise time you experience these symptoms will be compared to the ECG recording at that moment.

Post-Test

When the test is finished, you will either return to the Holter lab to have the equipment removed, or will remove the equipment yourself, and return it (and your diary) via a delivery service the lab employs.

After the Test

You should expect to hear from your doctor within a few days with the results and to discuss possible next steps.

If you experience skin irritation from the electrodes (which is uncommon), call the Holter lab to discuss what to do about it.

Interpreting Results

Your doctor should either contact you with the results or should pre-schedule a return visit to discuss the results of your Holter study. 

In interpreting the results of a Holter study, it is important to remember that the most common purpose of this study is to decide whether your unexplained symptoms are due to a cardiac arrhythmia—or not. This means that actually correlating symptoms to a simultaneous arrhythmia is critical to making the diagnosis.

Many people (most people, in fact) have occasional, benign types of arrhythmias that do not cause any symptoms at all. Seeing such an arrhythmia on the Holter report, without simultaneous symptoms, indicates that this arrhythmia is not causing a problem, and (usually) does not require any treatment of further evaluation.

On the other hand, when symptoms are well-correlated with a cardiac arrhythmia, that’s an arrhythmia that is causing a problem (at the very least, it is producing symptoms), and that deserves to be addressed.

Your doctor may also discuss with you other results shown on the Holter monitor report, including your maximum, minimum, and average heart rate, the total number of premature atrial complexes (PACs) and premature ventricular complexes (PVCs) you may have had, and any episodes of possible ischemia.

If you are having a Holter study to look for silent ischemia, finding strong signs of ischemia on the test will likely lead either to further testing (perhaps with a nuclear stress test or a cardiac catheterization), or to a change in your anti-ischemia therapy.

A Word From Verywell

The Holter monitor study is the most widely used type of ambulatory ECG monitoring. The test is quite good at diagnosing transient cardiac arrhythmias that generally occur during any given 24-48 hour period, and is very safe.

Was this page helpful?
Article Sources
  • Crawford MH, Bernstein SJ, Deedwania PC, et al. ACC/AHA Guidelines For Ambulatory Electrocardiography: Executive Summary And Recommendations. A report of the American College of Cardiology/American Heart Association task force on practice guidelines (committee to revise the guidelines for ambulatory electrocardiography). Circulation 1999; 100:886.
  • Barrett PM, Komatireddy R, Haaser S, et al. Comparison of 24-hour Holter monitoring with 14-day novel adhesive patch electrocardiographic monitoring. Am J Med 2014; 127:95.e11. doi: 10.1016/j.amjmed.2013.10.003.