Atrial Fibrillation, Explained

What happens

• In AFib, chaotic electrical signals make the heart's upper chambers quiver, so the heartbeat becomes irregular and often fast.
• Some people feel a racing or fluttering heartbeat, tiredness, breathlessness or dizziness, but many feel nothing at all.
• Blood can pool and clot in the left atrium; a clot that travels to the brain causes a stroke. AFib can make a stroke up to five times more likely.
• A smartwatch alert is a clue, not a diagnosis. Confirming AFib needs an ECG reviewed by a health professional.
• Treatment aims to prevent stroke (often with a blood thinner) and control the heartbeat with medicines, cardioversion or ablation.

Know the warning signs

• A racing or irregular heartbeat with chest pain
• Fainting
• Severe shortness of breath
• Stroke signs (FAST): face drooping, arm weakness, speech slurred or jumbled

Call 9-1-1 or your local emergency number right away. For stroke signs, note the time they started.

Call 9-1-1 or your local emergency number.

What you can do

• Keep your blood pressure in check.
• Drink less alcohol, or none at all.
• If you carry extra weight, losing about 10% of it can mean fewer AFib episodes.
• Stay active, and don't smoke.
• If you snore loudly or stop breathing in your sleep, ask to be checked for sleep apnea.
• Check your pulse now and then, and tell your health care provider if it feels irregular.

Common questions

Is atrial fibrillation dangerous?

AFib itself is not usually immediately life-threatening, but it matters. Blood can pool and clot in the heart, and AFib can make a stroke up to five times more likely. Over time, a fast, irregular heartbeat can also lead to heart failure. Treatment lowers these risks, so it's worth getting checked.

Can my smartwatch tell me if I have AFib?

Some smartwatches can flag a possible irregular rhythm, and that's a useful clue. But it's not a diagnosis. Confirming AFib needs an ECG, a recording of the heart's electrical signals, reviewed by a health professional. If your watch alerts you, talk to your health care provider.

Why do people with AFib take blood thinners?

Because the upper chambers quiver instead of squeezing, blood can pool and form clots that may travel to the brain. Depending on your stroke risk, your health care provider may offer an anticoagulant (blood thinner), which lowers the risk of stroke by about two thirds. Aspirin alone is not recommended for this.

Transcript

Most of the time, your heart keeps a steady rhythm, like a drummer keeping time. But for millions of people, that rhythm sometimes falls apart.

The beat becomes fast, fluttery and irregular. It's called atrial fibrillation, or AFib, the most common kind of irregular heartbeat. Let's see what happens when the heartbeat loses its rhythm, and what you can do about it.

Your heart has four chambers. The two upper chambers, the atria, collect blood and fill the two strong pumps below, the ventricles.

Every normal beat starts with a tiny electrical spark from the SA node, the heart's natural pacemaker. The spark sweeps across the atria in one neat wave, and they squeeze together.

Then the signal passes through the AV node, a gatekeeper, and on to the ventricles. They pump in a steady rhythm, usually sixty to a hundred beats a minute at rest.

In AFib, the spark no longer spreads in one neat wave. Instead, chaotic electrical signals swirl around the atria, firing hundreds of times a minute.

The atria can't squeeze properly. They just quiver, like a bowl of jelly. That quivering is what fibrillation means.

The AV node can't pass along every signal. So the ventricles beat irregularly, with no steady pattern, and often too fast.

How does it feel? Some people notice a racing, pounding or fluttering heartbeat. Others feel tired, short of breath, dizzy or weak.

But many people feel nothing at all. AFib can be silent, and may be found only at a routine check-up.

So why does it matter? When the atria quiver instead of squeeze, blood moves sluggishly. It can pool in a small pouch off the left atrium, called the left atrial appendage.

Pooled blood can form a clot. If the clot breaks loose, the heart pumps it out, and it can travel to the brain and block an artery. That's a stroke.

That's why AFib can make a stroke up to five times more likely. And it's why preventing stroke is a top goal of AFib care.

Over time, a fast, irregular heartbeat can also tire out the heart muscle, and lead to heart failure.

Anyone can get AFib, but it becomes more common with age. Other risks include high blood pressure, heart disease, sleep apnea, drinking alcohol, obesity, diabetes and an overactive thyroid.

Checking your pulse can help. Rest two fingers on the inside of your wrist. If the beat feels irregular, with no steady pattern, tell your health care provider.

Some smartwatches and home devices can also flag a possible irregular rhythm. But that's a clue, not a diagnosis. Confirming AFib needs an ECG, reviewed by a health professional.

If you have AFib, treatment has two main goals. First, prevent stroke. Depending on your risk, you may be offered a blood thinner, called an anticoagulant. It lowers the risk of stroke by about two thirds.

Second, control the heartbeat. Some medicines slow a racing heart. Others help keep a normal rhythm.

Doctors can also reset the rhythm with a brief, controlled shock, given under sedation. That's called cardioversion. Or, a procedure called ablation uses a thin tube inside the heart to make tiny scars that block the stray signals.

Call 9-1-1 or your local emergency number if a racing or irregular heartbeat comes with chest pain, fainting, or severe shortness of breath.

And know the signs of a stroke. Think FAST. Face drooping. Arm weakness. Speech that's slurred or jumbled. Time to call 9-1-1, right away.

Now for the good news. Healthy habits can lower your chance of getting AFib, and help keep it under control if you have it.

Keep your blood pressure in check. Drink less alcohol, or none at all. And if you carry extra weight, losing about ten percent of it can mean fewer AFib episodes.

Stay active, and don't smoke. And if you snore loudly, or stop breathing in your sleep, ask to be checked for sleep apnea.

One common myth: if I can't feel my AFib, it must be harmless. In fact, silent AFib can still cause a stroke. So take your treatment as prescribed, even when you feel fine.

So, to recap. In AFib, the upper chambers quiver. The heartbeat turns irregular. Clots can form and cause a stroke. And treatment and healthy habits lower that risk.

Now you know what happens when the heartbeat loses its rhythm. Check your pulse now and then, and keep listening to your heart.

Sources

1. Joglar JA et al. 2023 ACC/AHA/ACCP/HRS Guideline for the Diagnosis and Management of Atrial Fibrillation. Circulation 2024
2. Andrade JG et al. 2020 CCS/CHRS Comprehensive Guidelines for the Management of Atrial Fibrillation. Can J Cardiol 2020
3. American Heart Association — What is Atrial Fibrillation?
4. American Heart Association — Why Atrial Fibrillation Matters
5. Heart & Stroke Foundation of Canada — Atrial fibrillation
6. Heart & Stroke Foundation of Canada — Signs of stroke (FAST)
7. Perez MV et al. Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation. N Engl J Med 2019
8. Hart RG et al. Antithrombotic therapy to prevent stroke in atrial fibrillation. Ann Intern Med 2007