Does Screening For Silent (Subclinical) Atrial Fibrillation Make Sense Anymore?

The abnormal heart rhythm, atrial fibrillation (AF), often occurs silently. The individual experiencing it feels no symptoms.

For those of us over age 55 years there is a lifetime risk of developing (AF) of 37%. and with AF comes a fivefold risk of stroke which can be reduced by oral anticoagulant therapy.

Because up to 25% of AF is asymptomatic it seemed reasonable to me and many investigators in the field 10 years ago that screening for AF, especially in high-risk individuals would be worthwhile. If silent AF was detected in an individual, the logic went, we could then give appropriate treatment to prevent the strokes that AF is associated with.

Using that logic I wrote in 2014 a post entitled ” Take Your Pulse and Prevent A Stroke.”

AF detected by screening (whether by pulse, ECG or a wearable) and AF detected only by implanted devices (pacemaker, defibrillator, or implanted monitor) share many similarities. For both, if we seek them we shall find them.

One study showed in patients with no history of AF undergoing new pacemaker implantation during a mean follow-up period of 596 ± 344 days, 77 (29%) patients had at least one AF episode lasting ≥ 5 min.

AF found in individuals without symptoms by screening or from monitoring a patient’s pacemaker (or other implanted device with monitoring capabilities) is termed subclinical atrial fibrillation (SCAF.)

Newer Research Shows No Benefit of Screening for AF

The skeptical cardiologist wrote on new research in SCAF in 2020 in a post entitled “Subclinical Atrial Fibrillation: Seek and Ye Shall Find, But What Then.”

In 2020 there was no consensus on 1) whether we should screen for SCAF 2) if we should screen for SCAF, how should we do it 3) whether individuals with SCAF  found by screening should be treated with oral anticoagulants just as we treat clinical AF patients.

Two abstract presentations caused me to begin questioning the value of screening for AF:

• The mHealth Screening To Prevent Strokes (mSTOPS) study found that 2-week patch type monitoring of asymptomatic high-risk individuals resulted in a three-fold increased rate of AF detection along with higher rates of anticoagulation therapy but no difference in stroke at one year.
• Early results of the Danish randomized controlled trial LOOP (Atrial Fibrillation Detected by Continuous ECG Monitoring) study, which randomized subjects  ≥70 years of age and with ≥1 of the following stroke risk factors: hypertension (HTN), diabetes, heart failure, or previous stroke, in a 1:3 ratio to receive an implanted loop recorder (ILR) (Reveal LINQ; Medtronic) with continuous electrocardiographic monitoring or to standard of care.

In LOOP 35% of participants had SCAF lasting>6 minutes. However, the AF burden was low, and progression was limited. In addition, symptoms were scarce, and the heart rate was only modestly elevated during SCAF.

The final results of LOOP were published in Lancet in 2021 and again ILR screening resulted in a threefold increase in atrial fibrillation detection and anticoagulation initiation but no significant reduction in the risk of stroke or systemic arterial embolism.

The authors suggested enthusiasm for using ILRs like LINQ to detect silent AF (which had been burgeoning) should be curbed.

However, the genie was already out of the bottle, (thanks to heavy promotion by ILR makers) because ILRs are simple to implant¹ and they reap substantial monetary gains for implanters, monitor makers, and health care systems.

(Of note, funding for many studies in this area comes from either makers of monitor devices like the Zio patch (iRhythm) used in mStops or the Medtronic loop recorder used in LOOP which detect SCAF or makers of the blood thinners doctors would be prescribing if SCAF is detected (like Janssen the maker of Xarelto.))

Should We Intensively Seek AF after unexplained strokes?

One area where ILR implantation has been heavily promoted is in those patients who have had a stroke. One might anticipate that cardiologists who implant ILRs would strongly recommend them following an unexplained stroke but for some reason many neurologists began sending stroke patients to cardiologists a few years ago with the sole purpose of having an ILR implanted.

Often, cardiologists would implant the ILR without having performed a 2 or 4 week noninvasive monitoring of cardiac rhythm.²

John Mandrola, the electrophysiologist turned critical thinker, continues to provide his readers at Stop and Think and Sensible Medicine here on substack with thoughtful, sensible analyses of clinical trials in cardiology and has weighed in on this topic many times.

I believe his weekly podcast, This Week in Cardiology, should be mandatory content for cardiology training programs to aid in fostering skeptical and critical analysis of the cardiology basis which will aid in reducing the seductive power of Big Pharma and Big Device

In last Friday’s podcast he touched on a number of areas that are relevant to individuals with known or suspected atrial fibrillation and gave his impression of the post-stroke ILR issue:

I don’t know about your hospital, but a lot of post-stroke expensive loop recorders get placed in ours. The purpose, of course, is to detect AF, use oral anticoagulation (OAC), and reduce recurrent stroke. It’s a good purpose. People are well-intentioned.

Yet, the financial incentives are huge. I am not sure how it happened, but the hospital makes money, the doctor makes money, and there is a recurring revenue stream every month when the device is downloaded. Many patients have complained to me that they get monthly co-pays.

Studies, like the famous CRYSTAL AF, show that longer-term monitoring detects more AF than short-term monitoring. But we don’t have outcome data? Does the expense of implantable loop recorder (ILR) use result in fewer strokes? This is an especially relevant question now that we have incredibly persuasive data, from LOOP, NOAH, ARTESIA, that short-duration asymptomatic AF, you know, the kind you pick up on an ILR, confers a very low yearly stroke rate.

What’s more, many patients who receive a post-stroke ILR never have AF detected.

Mandrola discusses a recently published meta-analysis of 75 studies with 58 prediction models which could not find any combination of clinical or ECG factors that could predict patients who would have AF after a stroke and concludes:

Post-stroke monitoring I think is a well-intentioned endeavor, but empirical data is weak. This meta-analysis suggests that many people have tried to find a constellation of symptoms that will predict AF, but none are reliable enough to use clinically.

Something caused a clot in the brain arteries of these folks with strokes in whom we can’t find a cause³ so why not just give them blood thinners and forget about seeking AF? Turns out this approach has also been disproven.

Other people have tested the idea that we should just use oral AC in patients with embolic stroke of unknown origin. This too makes perfect sense, because, when you see an embolic stroke and there is no obvious atherosclerotic source, it must be due to a clot somewhere else and OAC should work. Except it doesn’t. Three RCTs, RESPECT-ESUS  (dabigatran), Navigate ESUS, (rivaroxaban) and last year ARCADIA (apixaban) all failed to reduce recurrent stroke.

I agree with his conclusions, in particular, the need to perform a study in this ESUS population before putting them through prolonged and intrusive testing to find AF which is of uncertain significance.

Therefore, to me, the obvious solution is to randomize stroke patients without an atherosclerotic source to ILR monitoring vs ECG patch recording or even home ECG recording and measure outcomes. It will take a big sample, but it’s doable.

Indeed, given the uncertainty, the only post-stroke patients receiving ILRs should be in randomized trials that help us understand who, if any, benefit from them.

Unobtrusively and Inexpensively Yours,

-ACP

1. You don’t need to be a cardiologist or a doctor to perform ILR implantations. When the LINQ ILR was approved I attended a brief training session where we practiced the insertion technique. You could also learn from watching a 10 minute video. I decided not to perform this service for my patients as I felt it would bias me toward recommending the procedure. A paper published in 2023 described an APP-led ILR program and yields insight into motivations that drive inappropriate ILR implantation
   ” Although there is a 15% loss of professional revenue with some insurers by using the APP ILR implant/explant program, this does not affect hospital compensation, which has the greater benefit. This program creates a robust cardiac monitoring program with excellent communication to patients and their referring providers. Downstream benefits include monthly billable report interpretations, prompt results leading to improved patient care, and increased generation of other EP procedures such as pacemaker, implantable cardioverter-defibrillators, left atrial appendage closure implants, and ablation procedures https://pmc.ncbi.nlm.nih.gov/articles/PMC1003029 ↩︎
2. My practice has been to have patients with unexplained stroke wear a 2 week patch-type monitor. If that is negative I don’t recommend ILR, even if the patient was referred by a neurologist for that purpose ↩︎
3. ESUS stands for embolic stroke of uncertain etiology. From the introduction to the 2019 RESPECT-ESUS trial: “ischemic infarctions account for the majority of strokes and are classified by their cause: large-artery extracranial or intracranial atherosclerosis, embolism from a cardiac source, small-artery occlusion, and other, less common causes. However, 20 to 30% of ischemic strokes are categorized as cryptogenic,and a proportion of these are further classified as embolic strokes of undetermined source if a pattern of infarction that suggests an embolic (nonlacunar) cause is present on brain imaging but no source for the embolus is identified after a series of tests is performed to try to find the source.” ↩︎