What Is an Implantable Loop Recorder (ILR)?

An implantable loop recorder (ILR) is a small, subcutaneous heart monitoring device designed to record and store your heart’s electrical activity over an extended period. It is primarily used to investigate unexplained fainting (syncope), infrequent palpitations, or suspected arrhythmias that have not been detected through standard heart tests such as ECGs or Holter monitors.

In this guide, we’ll explain what an ILR is, how it works, who needs one, how it's implanted, and what you can expect from the procedure and follow-up.

What Is an Implantable Loop Recorder?

An implantable loop recorder, also known as an insertable cardiac monitor (ICM), is a small device — roughly the size of a USB stick (about 4–5 cm in length and a few millimetres thick) — that continuously monitors your heart's electrical activity. It can automatically detect and record abnormal rhythms such as:

  • Bradycardia (slow heart rate)

  • Tachycardia (fast heart rate)

  • Atrial fibrillation (AF)

  • Pauses or irregular rhythms

The device stores recordings in its memory, which can be later reviewed by a cardiologist to diagnose or rule out potential arrhythmias.

Why Might You Need an Implantable Loop Recorder?

An ILR is recommended when traditional, short-term monitoring methods have not identified the cause of your symptoms. It is especially useful for detecting infrequent or unpredictable heart rhythm issues.

Common reasons for ILR implantation include:

  • Unexplained blackouts or fainting (syncope) after thorough investigation

  • Infrequent palpitations or dizziness

  • Suspected intermittent arrhythmias that haven’t been captured by ECG or Holter monitor

  • Stroke of unknown origin (cryptogenic stroke) to detect possible silent atrial fibrillation

Your cardiologist may suggest an ILR if episodes are occurring once every few weeks or months, making them difficult to capture with standard 24–48 hour monitoring tools.

How Is an ILR Implanted?

The ILR implantation is a quick and minimally invasive procedure, typically performed in an outpatient setting.

What to expect:

  • Local anaesthetic is applied to numb a small area on the chest, usually on the left side.

  • A small incision (around 1 cm) is made.

  • The device is inserted just beneath the skin using a special tool — the process takes less than 15 minutes.

  • No stitches are usually required; a sterile dressing is applied.

You can usually go home within an hour and return to normal activities the following day.

How Long Does an ILR Last?

Most modern ILRs can monitor your heart for up to 3 years continuously. They are powered by a long-lasting battery and store data automatically or when activated manually by the patient using a handheld monitor. At the end of the monitoring period, or once a diagnosis is made, the ILR can be removed through a similar quick procedure.

Remote Monitoring and Data Transmission

Many ILRs come with remote monitoring technology, allowing them to automatically transmit data to your heart specialist via a secure internet connection — often while you sleep.

This ensures:

  • Faster diagnosis

  • Fewer in-person visits

  • Early detection of serious arrhythmias

You’ll be provided with a home transmitter or a mobile app, depending on the ILR model.

Do ILRs Deliver Any Treatment?

No. Implantable loop recorders do not deliver any therapy — they are purely diagnostic tools. Their sole purpose is to record electrical activity and help identify if symptoms are linked to a cardiac arrhythmia.

If a significant heart rhythm issue is found, your doctor may recommend treatment options such as:

  • Pacemaker implantation

  • Catheter ablation

  • Medication management

  • ICD (Implantable cardioverter defibrillator), if needed

Is ILR Implantation Safe?

Yes. ILR implantation is considered a very safe procedure with a low risk of complications.

  • Potential but rare risks include:

    • Minor bleeding or bruising at the insertion site

    • Local infection

    • Discomfort or sensitivity at the device site

    These risks are typically mild and easily managed.

Key Benefits of an Implantable Loop Recorder

  • Continuous long-term heart monitoring

  • Ideal for detecting rare arrhythmias

  • Enables faster, more accurate diagnosis

  • Minimally invasive and well tolerated

  • Remote data transmission for real-time analysis

  • Can reduce the need for frequent ECGs and hospital visits

Still searching for answers about blackouts or palpitations?

A long-term heart monitor like an ILR could help identify the cause and give you peace of mind.
Contact Dr Li’s team today to schedule a consultation and find out if an implantable loop recorder is right for you.