The Facts About Atrial Fibrillation and Silent Stroke

by Matt McMillen Health Writer

If you have atrial fibrillation, or afib, then you know your risk of stroke is higher than normal. When your heart beats irregularly due to afib, blood can pool in your heart’s upper chambers and form clots. Those clots can travel to your brain and block an artery, causing a potentially debilitating stroke. But you don’t just have massive strokes to worry about—afib also appears to double your risk of silent strokes, so called because they have few if any noticeable symptoms. However, silent strokes can significantly damage your brain over time. Here’s what you need to know.

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What is a silent stroke?

Like all strokes, a silent stroke occurs when part of your brain’s oxygen supply gets cut off. But other types of stroke (more on those in just a moment) cause hard-to-miss symptoms like slurred speech, drooping face, and paralysis on one side of the body. No such obvious warning signs occur during a silent stroke, because the latter doesn’t tend to affect brain regions that control speech and movement. Instead, a silent stroke damages areas responsible for executive function—your ability to do things like plan, pay attention, and problem-solve, as well as manage your emotions.

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So what are the other types of stroke?

Ischemic strokes occur when a clot, which most often formed in the heart, travels to the brain. Once there, it blocks an artery and cuts off oxygen. A hemorrhagic stroke occurs when a blood vessel in the brain bursts. The blood that pours out damages brain cells and causes dangerous pressure to build. A transient ischemic attack (TIA), a.k.a. mini-stroke, has all the symptoms of a stroke, but it lasts only a short time and does no permanent damage. However, a TIA is a huge red flag that a full-blown stroke is very likely in your future.

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What causes a silent stroke?

The jury’s still out on this one, says Laurence Epstein, M.D., system director of electrophysiology at Northwell Health in Manhasset, NY, a specialist in afib and other arrhythmias. Clots may be one cause, but not the only cause, especially in people with afib, who may have blood vessels that don’t work as they should. This can make them more prone to blockages, such as those caused by atherosclerosis (plaque buildup) in the brain’s network of arteries, leading to chronic inflammation in the brain, which may also play a role. “Likely one answer does not fit all cases,” says Dr. Epstein.

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How common is silent stroke?

You don’t have to have afib to have a silent stroke. About one-quarter of people 80 and older will have one or more silent strokes, and for every full-blown stroke documented, researchers estimate 10 silent strokes occur. But because silent strokes have no noticeable symptoms, it’s unlikely you or your doctor will know you had one—making an accurate tally difficult to do. Cardiologist Andrew Freeman, M.D., of National Jewish Health in Denver, says they’re often diagnosed when you get an MRI of your brain for unrelated reasons, and your doctor notices the telltale brain lesions left by strokes.

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What harm does a silent stroke cause?

Silent strokes may not cause the devastating harm of a full-blown stroke (like speech and language problems, weakness, paralysis, and other major consequences that can leave you disabled and in need of ongoing care). However, silent strokes may increase your risk of a larger stroke, and if they continue to occur, the damage they cause will accumulate, boosting your chances of dementia and other types of cognitive impairment. Also, they’re not always entirely silent. Your symptoms may not be dramatic, says Dr. Epstein, “but it’s not really silent if you can’t think the way you used to.”

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How long, exactly, before silent strokes do real damage?

That will vary from person to person, and depend on where the strokes occur in the brain and just how small they really are. Sometimes, other parts of your brain can take over for the parts lost to stroke, so you don’t notice what’s been lost. In other cases, the brain damage may build up very gradually before it becomes obvious. “The changes are so subtle that you don’t see them,” says Dr. Epstein. “But someone who hasn’t seen you in two years may notice a dramatic difference.”

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Do blood thinners prevent silent stroke?

Maybe not fully. Anticoagulant medications (blood thinning medications) are the first, best line of defense against all types of strokes for people with afib because they help prevent clots and significantly lower the risk of a stroke. But anticoagulants may not offer the same level of protection against silent strokes—more evidence that clots aren’t the only culprit. Recent research found new brain damage in 5.5% of well-treated afib patients, most caused by silent stroke. That may help explain why people with afib are 34% more likely to develop cognitive impairment and dementia, even when they haven’t had a full-blown stroke.

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How else can I protect myself from having a silent stroke?

Dr. Freeman says that statins, drugs used to lower cholesterol, may help reduce silent strokes because they reduce inflammation. Dr. Epstein adds that signs of inflammation, such as elevated levels of c-reactive protein, can help predict your risk of having a silent stroke. But both doctors stress again the importance of anticoagulant therapy for people with afib. “Anticoagulants very significantly reduce your risk of any kind of stroke,” says Dr. Freeman. Even so, Dr. Epstein says, only half of people with afib take anticoagulants. Why? Likely because blood thinners don’t affect how patients feel, and they can cause excess bleeding.

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What can I do in addition to taking my prescribed medications?

Plenty! Exercise at least 150 minutes each week—even brisk walking counts! Eat a heart-smart diet. Choose fresh fruits, vegetables, whole grains, and other plant-based foods. You don’t have to go full vegetarian, but cut WAY back on fatty meat. Pick lean meats and fish instead. Swap butter and margarine for olive oil. Limit salt to keep your blood pressure down. And, do everything in your power to quit smoking. Such health hacks decrease your odds of silent stroke, and “the risk from making lifestyle changes is virtually zero!” Dr. Freeman says for added encouragement.

Matt McMillen
Meet Our Writer
Matt McMillen

Matt McMillen has been a freelance health reporter since 2002. In that time he’s written about everything from acupuncture to the Zika virus. He covers breaking medical news and the latest medical studies, profiles celebrities, and crafts easy to digest overviews of medical conditions. His work has appeared, both online and in print, in The Washington Post, WebMD Magazine, Diabetes Forecast, AARP, and elsewhere.