Insertable Cardiac Monitor (ICM) to Prevent Recurrent Stroke
The CRYSTAL-AF randomized control trial looked at patients who had a cryptogenic stroke (e.g., a stroke with no identifiable cause). These strokes, 20-40% of cases, account for nearly 175,000 ischemic (blocked artery in the brain) strokes every year in the U.S. (American Stroke Association).
This type of stroke i.e., undetected, can be caused by Silent Atrial Fibrillation.
In this study, patients received an Insertable Cardiac Monitor (ICM), such as the Medtronic Reveal LINQ loop recorder, to detect A-Fib. It’s inserted under the skin and works 24/7 for three years. [I have one. It’s very small and not noticeable.]
By detecting silent A-Fib, ICMs lower the risk of a patient having a second stroke. (23% of stroke survivors have a second stroke.)
Nine-Fold Higher A-Fib Detection Rate
The CRYSTAL-AF study found that using ICMs provided a nine-fold higher A-Fib detection rate compared with the standard treatment (e.g.: intermittent ECG and Holter monitoring).


This finding led many patients who had experienced a stroke of unknown cause (cryptogenic), to start taking anticoagulants. [Truth be told, most people who have a stroke and survive it are put on anticoagulants or Antiplatelets and don’t have to be motivated to take them.]
A similar study using the Zio monitor, iRhythm Technologies, Inc., found similar results. While wear time in the study with the Zio patch was up to 4 weeks, an ICM lasts for 2-3 years.
ICMs Improve Quality of Life and People Live Longer
In the CRYSTAL-AF study comparing immediate ICM use versus standard treatment of intermittent ECG and Holter monitoring, patients showed a benefit in quality-adjusted life-year (QALY) of 0.198 and an improvement of 0.226 in life years.
The ICM approach was projected to lead to 60 fewer lifetime ischemic strokes per 1,000 patients. And ICM was shown to be a cost-effective monitoring strategy.
A-Fib Stoke: Higher Risk if Age 65+
If you have an A-Fib stroke and survive, you have about a 50% higher risk of remaining disabled or handicapped (compared to stoke patients without A Fib).
MRIs often show permanent lesions on the brain from the stroke, even if the patient recovers.
All too many people 65+ have a stroke of unknown cause. Only after they have a stroke and survive it, do they find out they had “silent” A-Fib, and that it probably caused their stroke. But obviously, at that point, it’s too late.
CRYSTAL-AF: Find A-Fib Before a Second Stroke
From a public health standpoint, the CRYSTAL-AF study highlights the need to check if a stroke patient has Atrial Fibrillation and treat in time to prevent a second stroke.
“Atrial fibrillation after cryptogenic stroke [of undetermined source] was most often asymptomatic and paroxysmal and thus unlikely to be detected by strategies based on symptom-driven monitoring or intermittent short-term recordings.” -Sanna, et al. NEJM
Editor’s Comments



Danger of Anticoagulants: The CRYSTAL-AF model assumes that all patients would start taking a NOAC ( anticoagulant) once A-Fib is diagnosed.
But should everyone over 65 with silent A-Fib be on anticoagulants? Remember: anticoagulants are high risk drugs and can cause problems such as hemorrhagic strokes. i.e. bleeding in the brain. (See High Hemorrhagic Risk Factors from NOACs and Anticoagulants Increase Risk of Hemorrhagic-Type Strokes.)
Options for A-Fib Stroke Prevention: Beyond Drug Therapy. A-Fib patients have several options to prevent A-Fib strokes rather than having to take anticoagulants (NOACs).A-Fib patients have several options to prevent A-Fib strokes rather than having to take anticoagulants (NOACs).
The most obvious one is to become A-Fib free through a catheter ablation. You can’t have an A-Fib stroke if you no longer have A-Fib.
Another option is to close off or cut out the Left Atrial Appendage (LAA) where most A-Fib clots originate (strategies include the Watchman device or AtriClip heart surgery).
A third option is natural blood thinners such as Nattokinase, even though they haven’t been tested as much as NOACs.
ICMs Detect Silent A-Fib and Save Lives: Insertable Cardiac Monitors (ICMs) can tell doctors (and patients) if someone has “silent” A-Fib, i.e. without any apparent symptoms. Silent A-Fib accounts for 20%-40% of strokes.Could lives be saved and brain damage avoided if everyone reaching age 65 could be given an ICM?
How many people over age 65 have silent A-Fib? How many lives could be saved and brain damage avoided if everyone reaching age 65 could be given an ICM? ICMs aren’t very expensive, especially when one considers the alternative.
From a public health standpoint, we need a concerted effort to educate doctors and patients on the dangers of silent A-Fib strokes and how to reduce the risk.
The Routine EKG May Not be Enough: Compared to getting a routine EKG at your doctor’s office, ICMs are much more effective at detecting silent A-Fib. Perhaps consumer devices like the Apple Watch can provide this same info.