Implantable loop recorders

20 July 2025 | Dr Boon Lim

What is an implantable loop recorder (ILR)?

An implantable loop recorder (ILR) is a small device that is implanted under the skin to continuously monitor any abnormal heart rhythms. An ILR can automatically record any fast or slow heart rate and/or to store information such as your symptoms by simply pressing a button on a special activator. You will be taught how to use the activator after your ILR implant. Most ILR batteries last between two to four years. After the battery expires, you will be advised to have the ILR removed. However, your ILR may be removed sooner and replaced with a device such as a pacemaker, if the ILR identifies significant heart rhythm abnormalities which need treatment.

The ILR is particularly useful for understanding if your symptoms of intermittent dizziness or fainting (syncope) occur as a result of fast heart rhythms (tachycardia) or slow heart rhythms (bradycardia). Patients who have intermittent symptoms which occur rarely may be recommended to have an ILR implantation

Why has an ILR been recommended for me?

You may have experienced regular, unexplained episodes of syncope (loss of consciousness) that neither an electrocardiogram nor Holter monitoring can identify in that instance because these episodes occur so infrequently.

An ILR will be particularly helpful to determine if these symptoms are related to your heart, and will be able to detect slowing of your heart rhythm (bradycardia) during your episode of syncope.

In addition, an ILR is also useful in monitoring someone who has :

• atrial fibrillation (irregular and fast heart beats arising in the top chambers of the heart)
and/or

• ventricular tachycardia (regular and fast heart beats arising in the bottom chamber of the
heart).

• previous ischaemic stroke

Are there alternatives to having an ILR implantation?

An ILR implantation will only be requested by your doctor if they feel that this is the best way to monitor and find out more information that can contribute to your symptoms for the (approximately) three to four-year period. Typically your doctor will organise an ILR if your symptoms are sufficiently infrequently (ie occuring less than once a week).

Other alternatives to ILR are getting a repeat 7-day event monitor or 24- hour/48-hour Holter monitor that record your heart rhythm – but there may only be a limited number of tests which can be performed by your doctor. In other words, it may not be suitable for you to have repeated 24 or 48 hour Holter monitors as the yield (or ability to pick up a heart rhythm abnormality during a symptom episode) is very low.

What are the risks and complications of having an ILR implantation?

The risks involved in having the procedure will vary from patient to patient depending on your
medical history.

However, the overall risk is extremely low (i.e <1%, less than 1 in 100 patients will develop a complication). Your ILR implanting team or doctor will discuss these risks with you prior to the implant procedure and you will be asked to sign a consent form. Complications may include:
• bleeding or bruising
• risk of infection. This generally occurs within the first few weeks after implantation.

In the rare event you develop a complication, some symptoms include pain, swelling and redness or oozing at the wound site
• skin erosion causing unhealed wound that can result in the ILR device being removed

How long does an ILR implant take and how soon can I leave the hospital or clinic after the procedure?

An ILR implant typically takes around 10-15 minutes to perform. This is a short procedure performed in sterile conditions, under local anaesthesia. Following consent, you will be brought into the implanting room, and asked to lie down on a medical table, and have your chest exposed. The implant is inserted superficially typically slightly to the left of your breastbone (ie close to the centre of your chest), typically at the level just below your armpit. Once local anaesthetic is injected into the skin, a small incision is made and the ILR is then implanted using an ILR implant tool (as seen in the video above). Once the ILR implanted, the skin will be held together, and typically closed using steristrips (surgical “band-aids”) to hold the edges of the small wound together and then a waterproof dressing applied. This can usually be taken off after 3-5 days.

You will be able to leave hospital after a period of monitoring (typically 20-30minutes) to ensure you are comfortable and the site is not bleeding.

You will also be given clear instructions about how to use the device – and if relevant, you will be given instructions on pairing your mobile phone to the device to transmit data, or be given a “device base” which can be plugged in by your beside to allow daily automatic transmission of data to your clinic or hospital.

Patient information videos

Below are 2 videos detailing a patient experience of having an ILR implant, and Consultant Cardiologist Dr Boon Lim, explaning more about the ILR device, including why it may be recommended, how it is implanted and what some of the risks / complications are.

I've had a stroke, and my stroke doctor has asked me to have an ILR? Is this neccessary?

A stroke happens when part of the brain suddenly loses its blood supply—either because a blood vessel is blocked (ischemic stroke) or because it ruptures and bleeds (hemorrhagic stroke). A transient ischemic attack (TIA) causes similar symptoms but resolves quickly because the blockage is temporary.

Finding the underlying cause of a stroke is crucial: the best strategy to prevent another stroke depends on why the first one happened.

In some patients, even after an extensive evaluation, no clear cause is identified. These are often called cryptogenic strokes or embolic strokes of undetermined source (ESUS).

A common “hidden” culprit is intermittent (paroxysmal) atrial fibrillation (AF)—an irregular heart rhythm that may produce no symptoms and can come and go, making it easy to miss on short-term heart monitoring.

Implantable loop recorders (ILRs) can continuously track heart rhythm for years. They substantially increase the chances of detecting infrequent, silent non-symptomatic AF episodes in people who have had a stroke of unknown cause.

Detecting AF matters because timely anticoagulation (blood‑thinning medication) can dramatically reduce the risk of another, potentially larger, or fatal stroke.

In summary, if your stroke doctor has recommended that you have an ILR implanted, we would strongly urge you to follow the advice of your stroke doctor.

In the video below, Dr Boon Lim, Consultant Cardiologist at Imperial College talks about why patients who have had strokes may be recommended an ILR, and what to expect from having the procedure.