A Holter monitor or ambulatory ECG is a portable device that records the heart’s electrical activity continuously while you go about normal life — capturing the rhythm over hours to days, rather than the few seconds of a resting ECG. It is used to catch rhythm problems that a short recording might miss, such as palpitations, blackouts, dizziness or a suspected irregular heartbeat, and to monitor a known rhythm problem or a treatment. A useful rule of thumb: the less often symptoms happen, the longer the monitoring needed.
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In a medical emergency, or for severe or sudden symptoms such as breathing difficulty, chest pain, fainting or stroke signs, call 995 immediately.
The monitor records the heart but does not treat it or alert anyone in real time. Call 995 immediately — while wearing it or at any time — for fainting or collapse, severe or crushing chest pain, or severe breathlessness; do not wait for the device to “catch” an emergency. If it has an event button, press it and note the time, but get emergency help first.
What it is and why it is done
A Holter monitor is essentially a wearable, longer version of an ECG. It records continuously while you do your normal activities, which lets it capture rhythm problems that come and go and would rarely appear during the brief snapshot of a resting ECG. Doctors use it for palpitations, fainting or dizziness, a suspected arrhythmia such as atrial fibrillation, and to check how a known rhythm problem or its treatment is behaving.
The types
A standard Holter is a small recorder with chest electrodes, worn typically for 24 to 48 hours, though it can be up to about seven days. Longer patch monitors are adhesive patches worn for several days up to a week or two, for symptoms that occur less often. Event or loop recorders are worn for weeks and activated when symptoms strike, and some are implanted for months for very infrequent episodes. Which one is chosen depends mainly on how often your symptoms happen.
How it works and what to expect
Small sticky electrodes or patches on the chest connect to a lightweight recorder worn on a belt or clip, or, for patch types, stuck to the chest. You wear it during normal daily activities — work, walking and sleep — because the whole point is to record your ordinary life. With a traditional recorder you generally cannot bath or shower while wearing it, so keep it dry; some newer patches are water-resistant, so follow the specific device’s instructions. Men may have small areas of chest hair shaved so the electrodes stick, and mild skin irritation under the stickers is possible.
The symptom diary
Keeping a symptom diary is the single most useful thing you can do to make the test count. Write down what you felt and the exact time — palpitations, dizziness, breathlessness or fainting — along with what you were doing, such as climbing stairs, resting or sleeping. This lets the cardiologist line your symptoms up against the heart trace at that moment and see whether they are linked. If the device has an event button, press it when symptoms start and note the time.
What results mean and their limits
The recording is analysed afterwards, with results usually taking from a few days to a few weeks. It may capture an irregular rhythm — showing how often and how long it lasts and whether it links to your symptoms — or it may be normal. The key limitation is that a normal result only means no abnormal rhythm occurred during the monitored window; it does not fully rule out an intermittent problem. If your symptoms did not happen while you were wearing it, a longer or repeat monitor, or an event recorder, may be recommended — and this is normal, not a sign anything was done wrong.
Red flags
Because the monitor records rather than treats, and does not summon help, you should call 995 immediately — while wearing it or at any time — for fainting or collapse, severe or crushing chest pain, or severe breathlessness. Pressing the event button and noting the time is helpful, but always secondary to getting emergency help. It is also worth contacting the clinic if an electrode falls off or the recorder stops working, so the study is not wasted.
Getting one in Singapore
A Holter monitor or ambulatory ECG is usually arranged through a GP referral to a cardiology clinic or hospital, which fits the device and analyses the recording. It is painless — you feel only the sticky electrodes, with no electricity or discomfort from the device itself. HealthHub offers trusted general information, and our ECG guide explains the standard resting test that a Holter extends over time. The most useful thing you can bring to the test is not the device but your attention: wearing it during your genuine, normal routine and keeping an honest symptom diary gives the cardiologist the best possible chance of matching how you feel to what your heart is actually doing — which is exactly the question a Holter is designed to answer. If nothing shows up this time, that is common and not a dead end; longer or repeat monitoring, or an event recorder, can be arranged to keep looking for an intermittent rhythm.
Related tests & diagnostics topics
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- Echocardiogram (heart ultrasound)
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- Stool tests explained
- Contrast scans & dye
- Biopsy: what to expect
- Home blood-pressure monitoring
- ECG (electrocardiogram)
- GP clinics in Singapore
Sources
- NHS — Electrocardiogram (ECG), including ambulatory ECG: nhs.uk
- NHS — Echocardiogram: nhs.uk
- HealthHub Singapore: healthhub.sg