What is a Holter monitor and when is it used?

A Holter monitor is a small, portable ECG recorder that you wear while going about your normal day. It records every heartbeat continuously, usually for 24 to 48 hours and sometimes for up to a week, through sticky electrodes on your chest. It is used when someone has symptoms that come and go, such as palpitations, dizziness or blackouts, which a standard ECG in clinic is unlikely to catch. The aim is to record the heart's rhythm at the exact moment you feel something, so the symptom and the rhythm can be matched.

A Holter monitor is also used to look for atrial fibrillation, to check how well heart rhythm treatment is working and to measure how often extra beats occur. The test is painless, carries no risk and does not stop you working, sleeping or exercising. In my clinics I use a traditional ambulatory ECG monitor worn for up to seven days, or a ZIO patch worn for up to 14 days, depending on how often a patient's symptoms happen.

Why a standard ECG is not always enough

I carry out a 12 lead ECG during every consultation. It takes a few minutes and gives a detailed picture of the heart's electrical activity at that moment. It can show signs of a previous heart attack, thickened heart muscle or a rhythm problem that is present all the time, such as persistent atrial fibrillation.

The limitation is that it only records around ten seconds. Most patients I see with palpitations feel completely normal when they are sitting in front of me, and their ECG is normal too. That does not rule out a rhythm problem. It simply means the problem was not happening during those ten seconds, which is why longer monitoring is needed.

When is a Holter monitor used?

The most common reasons I arrange heart rhythm monitoring are the following.

• Palpitations. A fluttering, pounding, racing or skipping sensation in the chest. Most palpitations are harmless, but some point to a rhythm problem that needs treatment.
• Dizziness and blackouts. Episodes of lightheadedness or fainting can be caused by the heart beating too slowly or too fast. Monitoring can show pauses in the rhythm or heart block, where the electrical signal is delayed or interrupted.
• Suspected atrial fibrillation. Atrial fibrillation often comes and goes in its early stages, and it raises the risk of stroke. Finding it matters because treatment can greatly reduce that risk.
• After a stroke or mini stroke. Monitoring is used to look for intermittent atrial fibrillation that might have caused it.
• Checking treatment. For people already on rhythm or rate controlling medicines, monitoring shows whether the treatment is working throughout the day and night, not just in clinic.
• Counting extra beats. Ectopic beats are very common and usually harmless, but a very high number can occasionally weaken the heart muscle over time. A monitor measures exactly how many there are.

What happens when you wear a Holter monitor

Having the monitor fitted takes around ten to fifteen minutes. A few small electrode stickers are placed on your chest, sometimes after a small area of hair has been shaved. Thin wires connect them to a recorder about the size of a small mobile phone, which clips onto a belt or hangs from a strap.

You then go home and carry on with your usual routine. In fact, it is important that you do, because the purpose is to record the heart during the activities that normally bring on your symptoms. If your palpitations happen when you climb stairs or play tennis, it helps to do those things while wearing the monitor.

You will be asked to keep a simple diary of any symptoms with the time they happened. Some monitors also have a button to press when you feel something. This diary is one of the most valuable parts of the test.

Traditional Holter monitors are not waterproof, so you will need to avoid baths and showers while wearing one. Most people manage with a strip wash for a day or two. When the recording period ends, you return the monitor and the data is analysed.

Holter monitor or ZIO patch?

The ZIO patch is a newer type of ambulatory ECG monitor. Rather than wires and a separate recorder, it is a single adhesive patch that sits on the left side of the chest. It is water resistant, so you can shower with it on, and it can stay in place for up to 14 days. NICE guidance on the ZIO XT found that it gives a higher diagnostic yield than a standard 24 hour Holter monitor, meaning it picks up more heart rhythm problems.

In my experience, a 14 day ZIO patch works better than a 24 hour Holter monitor for people whose symptoms come once or twice a week because a short recording will often miss them altogether. A normal 24 hour result in someone who did not have any symptoms that day tells us very little, and the patient ends up repeating the test. With two weeks of recording, the chance of capturing a typical episode is much higher.

For someone with symptoms every day, a 24 to 48 hour Holter monitor is usually enough and gives a quick answer. I've found that the most useful question I ask is simply how often the symptoms happen, because the right length of monitoring follows from that. For symptoms that occur less than once a fortnight, other options are better suited, such as a handheld event recorder, a medically validated smartphone ECG device or, occasionally, a small implantable loop recorder placed under the skin that can monitor for up to three years.

What the results can show

The recording is analysed to look at the heart rate throughout the day and night, the underlying rhythm, any pauses and any abnormal rhythms, and how all of this matches up with your diary.

Common findings include the following.

• Normal sinus rhythm. If you had your usual symptoms during the recording and the rhythm was normal throughout, that is very reassuring. It tells us the symptoms are not caused by a dangerous heart rhythm.
• Ectopic beats. Extra beats that cause a thud or skip. These are found in most healthy people and are rarely a concern unless very frequent.
• Atrial fibrillation. An irregular and often fast rhythm that needs assessment of stroke risk and treatment.
• Supraventricular tachycardia. Episodes of a regular, fast heartbeat that start and stop suddenly. These are often very treatable.
• Slow rhythms and pauses. These can explain dizziness or blackouts and may need a pacemaker.

From working with patients over more than 20 years, I've found that one of the most important outcomes of a heart monitor is reassurance. A large proportion of people with palpitations turn out to have harmless ectopic beats or a normal rhythm. Seeing the recording and knowing exactly what they are feeling often takes away much of the anxiety, which in itself can reduce how often the symptoms are noticed.

Making the most of your monitor

A few simple steps make the recording more useful.

• Keep to your normal routine, including exercise, so the monitor sees your heart under everyday conditions.
• Write down every symptom with the time and what you were doing, even if it seems minor.
• Note when you take any heart medicines.
• Avoid electric blankets and keep the recorder away from magnets, as these can interfere with the signal.
• Do not remove the electrodes or patch early unless your skin becomes very irritated.

Arranging heart rhythm monitoring

The BHF explains that Holter monitoring records your heart's electrical activity for 24 to 48 hours, sometimes longer. In my clinics, I can usually arrange ambulatory monitoring or a ZIO patch quickly after the consultation, and I go through the results with each patient alongside their diary. You can read more about the ambulatory ECG monitor, ZIO patch and other tests I offer on my heart tests page.

If you have palpitations, dizziness or blackouts, or you have been told you might have an irregular heartbeat, please contact me, Dr Arvind Vasudeva, to discuss whether heart rhythm monitoring would help. I see patients at Parkside Hospital in Wimbledon, The New Victoria Hospital in Kingston, Cleveland Clinic London and Heartsure in Kingston, and you can book an appointment at the location that suits you best.