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Posted on Tuesday August 12, 2025 in Naked Heart
An article written by Dr Edward Leatham, Consultant Cardiologist
Tags: Syncope, AFib, NH1, ECG search website using Tags to find related stories.
When unexplained fainting episodes (syncope) or certain types of stroke occur, the search for an underlying cause can be frustrating for patients and clinicians alike. In some cases, the usual tests — ECGs, Holter monitors, echocardiograms — return entirely normal results, leaving us with more questions than answers.
One increasingly important tool in solving these clinical mysteries is the implantable loop recorder (ILR) — a small device, implanted under the skin of the chest, that continuously records heart rhythm for up to three years. It has transformed our ability to detect rare, intermittent, and often silent heart rhythm problems that would otherwise go unnoticed.
This article will focus on ILRs in the context of syncope and cryptogenic (i.e., unexplained) stroke, TIA, and transient global amnesia (TGA) — with a particular emphasis on how they help detect subclinical atrial fibrillation and why that matters for stroke prevention.
The link between certain heart rhythm disorders and brain events is well established. In particular, atrial fibrillation (AF) and atrial flutter can cause blood stasis in the left atrial appendage (LAA), leading to blood clot formation.
Whether a clot forms depends on several factors:
Once a clot forms, it can detach — embolise — and travel through the aorta into the arteries of the brain. If it lodges in an end artery, blood flow is blocked, causing a stroke or TIA.
The size of the embolus determines how large a brain artery is blocked. The brain’s natural fibrinolytic system may dissolve small clots quickly, leading to a TIA rather than a permanent stroke. But larger clots, particularly those blocking the middle cerebral artery, often cause severe, lasting neurological damage.
With modern medicine, thrombolytic therapy can sometimes dissolve such clots if given rapidly after stroke onset. Nonetheless, prevention remains far better than cure.
Many people with atrial fibrillation have no idea they have it. This is because the atrioventricular (AV) node — the gatekeeper controlling electrical signals from the atria to the ventricles — behaves very differently in different people.
In some, the atrial rate during AF may be as high as 600 beats per minute, but the AV node allows through only a modest number of impulses, resulting in a ventricular (pulse) rate that feels almost normal. Without palpitations or breathlessness, AF can go entirely unnoticed.
Others have paroxysmal AF, where episodes come and go, sometimes lasting only hours or days before returning to a normal rhythm. This group is at particular risk of embolic stroke because even when the atria return to normal rhythm, there can be a period of atrial stunning — temporary mechanical inactivity of the LAA. During this time, pre-formed thrombus may be expelled into the circulation.
This explains why the highest risk period for embolic stroke after electrical cardioversion is around day two, unless anticoagulants are given.
Because of the above mechanisms, it is customary to investigate all patients with TIA, TGA, or stroke with:
However, even these extended tests may fail to capture rare AF episodes that happen only a few times a year — or even less frequently.
Consider a 65-year-old woman who presented with a TIA. All her investigations — ECG, blood pressure monitoring, Holter ECG, transoesophageal echocardiography — were normal.
The recommendation was to start anticoagulation based on probability that AF might be the cause. However, the patient declined, wishing for definitive evidence. She instead had an ILR implanted.
For three years, no abnormal rhythms were recorded during routine checks or via the home monitoring system. Just before the device was due for removal, it was read one final time. The result? She had been in continuous AF for the preceding week.
Although extreme, this case illustrates a vital point: paroxysmal AF can be extremely rare yet clinically significant, and only long-term monitoring can reliably detect it.
ILRs are equally valuable in investigating syncope — sudden, brief loss of consciousness due to temporary lack of blood flow to the brain.
Syncope can be caused by:
If initial tests (including Holter or event monitors) are inconclusive, an ILR offers a much higher chance of capturing the heart rhythm at the exact moment symptoms occur — especially when episodes are infrequent, separated by weeks or months.
From a health-economics perspective, fitting an ILR after one or two negative ambulatory recordings is cost-effective compared with the repeated expense of hospital admissions for unexplained syncope. It also has major implications for driving restrictions — a confirmed diagnosis can mean a more precise risk assessment rather than indefinite precautionary bans.
An ILR is a matchstick-sized device implanted under the skin of the chest, usually under local anaesthetic in a brief outpatient procedure. Once in place, it continuously monitors the heart’s electrical activity, storing recordings of any abnormal events it detects automatically or when triggered by the patient using a handheld activator.
Modern ILRs have:
An ILR may be recommended if you:
Benefits:
Limitations:
The ultimate goal of detecting subclinical AF is to prevent stroke. Once AF is confirmed, most patients at risk will benefit from anticoagulation to dramatically reduce the likelihood of a clot forming and travelling to the brain.
For patients with cryptogenic stroke, studies have shown that prolonged rhythm monitoring — particularly with an ILR — can double or triple the detection rate of AF compared with standard short-term monitoring.
For patients and clinicians facing the uncertainty of unexplained stroke or fainting, an ILR can be the missing piece of the diagnostic puzzle. It is not simply a piece of technology — it is a window into the heart’s behaviour over months and years, giving us the best chance of catching rare but dangerous arrhythmias before they cause harm.
The Naked Heart is an educational project owned and operated by Dr Edward Leatham. It comprises a series of blog articles, videos and reels distributed on Tiktok, Youtube and Instagram aimed to help educate both patients and healthcare professionals about cardiology related issues.
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An article written by Dr Edward Leatham, Consultant Cardiologist Tags: Podcast, AFib, Bradycardia, NH1 search website using Tags to find related stories. Introduction Pulse rate or heart rate is a fundamental metric of heart health. It’s easily accessible—whether through feeling the […]