Loop Recorders (ILRs)
Who is offered a loop recorder
When to see a cardiologist
How a loop recorder works
The loop recorder implant procedure
Living with a loop recorder
Complications of a loop recorder
Who Is Offered a Loop Recorder
Implantable Loop Recorders (ILRs) are common medical devices used to detect abnormal heart rhythms. Many thousands of people in the UK are fitted with a loop recorder every year.
ILRs are offered to patients who are likely to have a significant heart rhythm disorder which, if present, would require treatment. Two common uses are to diagnose atrial fibrillation in patients with a high stroke risk, and to diagnose the cause of infrequent faints or drop attacks.
For example: a patient who has had a stroke with no clear cause found might be offered a loop recorder to find out if they have asymptomatic atrial fibrillation (i.e. atrial fibrillation without symptoms). Many studies have shown that loop recorders tend to be more effective than other forms of heart monitoring in this situation.
Making a decision to have an ILR fitted is a matter of weighing up the small risks of having the device, versus the potential advantage of making a significant heart rhythm diagnosis. In the stroke example above, the advantage of making a diagnosis is that the risk of future strokes can be reduced by correct treatment. A cardiac electrophysiologist - or heart rhythm specialist - is ideally placed to help patients navigate these decisions.
When to See a Cardiologist
Symptoms such as intermittent palpitations, breathlessness, dizziness and chest pain may be caused by changes in the the heart rhythm (“arrhythmia”). Patients with these symptoms may be offered short periods of continuous ECG monitoring to help make the diagnosis. If conventional heart rhythm monitors fail to detect anything, or if the symptoms are very infrequent, then an ILR may be offered.
Patients with previous strokes are commonly offered an ILR to detect possible atrial fibrillation.
How an ILR Works
Modern ILR devices are about half the width of a little finger and a similar length. They sit under the skin just to the left of the breastbone and collect continuous information on the heartbeat. Batteries last for up to three years.
The heartbeat is recorded on a continuous loop (hence the name) so that the recording is constantly being overwritten. However, the ILR includes a computer with algorithms set to recognise any rhythms that are particularly fast, slow, or irregular (such as atrial fibrillation). If anything fitting these “algorithmic parameters” is detected, then a snapshot of this is logged in a more permanent memory and may be uploaded to a monitoring system and communicated to the patient’s cardiologist.
Most ILRs also include a way for a patient to tell the device that they’ve experienced symptoms (eg: lightheadedness, fainting or palpitations). For example ILRs made by Medtronic are supplied with a keyfob button device called a “patient assistant” that patients can use to tag symptom episodes. These symptom episodes are then stored and uploaded in the same way as any recordings made on basis of algorithmic detection. You can read about the Medtronic patient assistant and monitoring system here.
The ILR Implant Procedure
ILRs are generally fitted as an elective procedure but may also be carried out for patients already in hospital, typically after admission with a faint or loss of consciousness. ILR implant procedures are very quick and only rarely cause significant discomfort.
A small sterile field is placed over the chest and an injection of local anaesthetic given to the skin. Once the area is numb a cut about 7mm long is made and the ILR injected through this. The cut is usually closed with a single dissolvable stitch and a dressing applied. The wound is usually healed entirely within 7-10 days leaving a small "lump” around the monitor itself.
Living With an ILR
Once the implant wound has healed, living with an ILR carries very few restrictions. As with pacemakers and defibrillators, magnets can interfere with the function of ILRs and prolonged exposure to a magnet should be avoided.
If an ILR has been implanted to reach a diagnosis for unexplained symptoms, it is important that a patient uses any symptom logging equipment (eg: the Medtronic patient assistant device) as directed to log symptom episodes.
When the ILR battery runs out after three years or so, the device will usually be removed via a second procedure very similar to the implant procedure. The decision whether to replace it with a new ILR will depend on why the device was implanted in the first place.
Complications of ILRs
Serious complications related to ILR implant procedures are rare. Very occasionally an ILR may become infected and need to be removed. Sometimes the ILR can move under the skin and become uncomfortable. Again, removal may be considered for this problem. Some ILRs can interfere with diagnostic scans (CT and / or MRI) but with modern devices and scanning techniques this tends to be less of an issue than it once was.