An implantable loop recorder (ILR), also called an insertable cardiac monitor (ICM), is a small device implanted just under the skin of the chest that continuously records heart rhythm for up to four or five years. It is used to investigate unexplained blackouts, palpitations, or suspected arrhythmias that have not been captured by shorter monitoring methods.
How it works
The ILR is about the size of a small USB stick. It is inserted under local anaesthesia in a minor procedure that usually takes less than 30 minutes. The device records an ongoing ECG signal and automatically stores episodes when it detects an abnormal rhythm. It can also be activated by the patient using a small handheld activator when symptoms occur.
How data is retrieved
Most modern ILRs transmit data wirelessly to a bedside monitor each night, which sends the information to the clinical team automatically. This means arrhythmias can be detected without waiting for a clinic appointment. Some devices can send immediate alerts if a dangerous rhythm is detected.
When it is used after cardiac arrest
After a cardiac arrest where no clear cause has been identified, an ILR may be implanted (in addition to or instead of other investigations) to monitor for recurrent arrhythmias once the patient is stable. It is particularly useful when the cardiac arrest was not witnessed and the rhythm at the time was not documented. The ILR can provide insight into whether further arrhythmias occur during daily life.
Removal or replacement
When the battery nears the end of its life, or once the clinical question has been answered, the device is removed in a simple outpatient procedure. If monitoring needs to continue, a new device can be inserted.