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AF and blood thinners

What atrial fibrillation (AF) is, how the sources link it to stroke, what blood thinners and a left atrial appendage closure device are, how the sources describe bleeding, and questions to ask a care team.

Signs the sources say need care

Stroke symptoms MedlinePlus lists

  • Sudden numbness or weakness of the face, arm, or leg (especially on one side of the body).1
  • Sudden confusion, trouble speaking, or understanding speech.1
  • Sudden trouble seeing in one or both eyes.1
  • Sudden difficulty walking, dizziness, loss of balance or coordination.1
  • Sudden severe headache with no known cause.1

“If you think that you or someone else is having a stroke, call 911 right away.”2

MedlinePlus, National Library of Medicine, Stroke | CVA | Cerebrovascular Accident | MedlinePlus

In an emergency, call your local emergency number.

Signs the sources say need care

Examples of serious bleeding signs for blood thinners, from MedlinePlus

  • Menstrual bleeding that is much heavier than normal.3
  • Red or brown urine.3
  • Bowel movements that are red or black.3
  • Bleeding from the gums or nose that does not stop quickly.3
  • Vomit that is brown or bright red.3
  • Coughing up something red.3
  • Severe pain, such as a headache or stomachache.3
  • Unusual bruising.3
  • A cut that does not stop bleeding.3
  • A serious fall or bump on the head.3
  • Dizziness or weakness.3

“Call your provider if you have any sign of serious bleeding”3

MedlinePlus, National Library of Medicine, Blood Thinners | Anticoagulants (MedlinePlus)

In an emergency, call your local emergency number.

What atrial fibrillation (AF) is

  • Atrial fibrillation, called AF or AFib, is among the most common kinds of arrhythmia, a problem with how fast or how regularly the heart beats.4
  • In AF the heartbeat is irregular and at times much faster than normal.4
  • Some people with AF have no symptoms and do not know they have it.5, 6

AF and stroke

  • NHLBI says that in AF blood can collect in the heart, which makes clots more likely to form.6, 7
  • NHLBI adds that a clot can lead to a stroke or other complications.6, 7
  • MedlinePlus says AF can put a person at risk for stroke and other heart conditions.4, 7
  • MedlinePlus names stroke, heart failure, blood clots, sudden cardiac arrest, and cognitive impairment and dementia among the serious problems that untreated AF can lead to.8
  • MedlinePlus says AF and other heart diseases can cause blood clots that lead to stroke.9
  • MedlinePlus says the symptoms of a stroke often happen quickly and that they include the five listed in the stroke box.1
  • Neither NHLBI nor MedlinePlus gives a number for how much AF raises the risk of stroke.7

What blood thinners do

  • MedlinePlus describes blood thinners as medicines that stop blood clots from forming.10
  • MedlinePlus says blood thinners do not break up a clot that is already there, but they can stop it from getting bigger.10
  • MedlinePlus names atrial fibrillation among the conditions in which a person may need a blood thinner.11
  • NHLBI says people with a risk of stroke may need a blood thinner.12, 13
  • NHLBI gives warfarin and the direct oral anticoagulants (DOACs) apixaban, dabigatran, rivaroxaban and edoxaban as examples of blood thinners.12, 14, 15
  • NHLBI says these medicines stop clots from forming and lower the chance of a stroke.12, 15
  • MedlinePlus lists two types of blood thinners, anticoagulants and antiplatelets.16
  • In that list, anticoagulants, such as heparin or warfarin, slow the body's process of making clots.16
  • In that list, antiplatelets, such as aspirin and clopidogrel, keep platelets from clumping together.16
  • MedlinePlus adds that antiplatelets are mainly taken by people who have had a heart attack or stroke.16
  • MedlinePlus says blood thinners may interact with certain foods, medicines, vitamins and alcohol.17
  • MedlinePlus says regular blood tests may be needed to check how well the blood is clotting.17

The bleeding trade-off

  • MedlinePlus says bleeding is the most common side effect of blood thinners.3
  • MedlinePlus adds that blood thinners can also cause an upset stomach, nausea and diarrhea.3
  • NHLBI says blood thinners come with a risk of bleeding.12, 13
  • MedlinePlus says it is important to have enough medicine to prevent clots but not so much that it causes bleeding.17
  • The NHLBI and MedlinePlus pages give no numbers for how much blood thinners reduce the chance of stroke or increase the chance of bleeding.12
  • MedlinePlus gives its list of signs of serious bleeding as examples, and the list covers blood thinners in general, not only those used for AF.3

The left atrial appendage and its closure

  • NHLBI describes the left atrial appendage as a small sac within the wall of the left atrium.18, 19
  • The authors of the PROTECT AF trial write that embolic stroke in people with non-valvular AF is thought to be linked to clots in the left atrial appendage.20
  • NHLBI describes closing off the appendage, which it says may be done during surgical ablation or other heart surgery, as a way to stop clots from forming there and causing a stroke in people who cannot take blood thinners.18, 19, 21
  • NHLBI cautions that closing the appendage completely can be hard, and that any leak leaves some clotting risk.21
  • In the PROTECT AF trial, 707 adults with non-valvular AF were randomly assigned to one of two groups.22
  • One group had a WATCHMAN closure device placed and then stopped warfarin, and the other group took warfarin.22
  • The adults in the trial each had at least one of these: a previous stroke or transient ischemic attack, congestive heart failure, diabetes, high blood pressure, or an age of 75 or older.22
  • MedlinePlus describes a transient ischemic attack (TIA) as a condition similar to a stroke, in which the blood supply to the brain is blocked for a short time.23
  • The trial was reported in 2009, and this guide does not describe later versions of the device.22
  • The trial's main outcome was a combination of stroke, cardiovascular death and systemic embolism.22
  • On that outcome, the device group met the trial's pre-set test for not being worse than warfarin by more than an agreed margin, and that margin allowed up to double the warfarin group's event rate.22, 24
  • The range of possible results for the device compared with warfarin on that outcome included no difference, so the trial did not show that the device was better.22
  • Serious safety events, which included major bleeding, were more frequent with the device than with warfarin.22
  • The authors say the safety events in the device group mainly came from complications linked to the procedure.22
  • The trial registry lists being eligible for long-term warfarin as a requirement and having a medical reason not to take warfarin as a reason to be left out.22, 25
  • So the trial did not test the device in people who have a medical reason not to take warfarin.22, 25
  • The US Food and Drug Administration approved the original WATCHMAN device on 13 March 2015.26
  • The approval order says the device is meant to lower the risk of clots from the left atrial appendage in people with non-valvular AF.26
  • These are people at increased risk for stroke and systemic embolism by a risk score (CHADS2 or CHA2DS2-VASc) who are recommended for anticoagulation therapy.26
  • They are also deemed by their physicians to be suitable for warfarin.26
  • In addition, they have an appropriate rationale to seek a non-drug alternative to warfarin, taking into account how safe and effective the device is compared with warfarin.26
  • That is the original approval, and FDA records list many later supplements, including newer device versions, that this guide does not describe.26
  • NHLBI describes closing off the appendage for people who cannot take blood thinners, but the 2015 FDA approval order for the original WATCHMAN device is for people who are suitable for warfarin and have a reason to seek an alternative.19, 26
  • This guide does not reconcile the two descriptions, and the sources read here do not explain the difference.19, 26

What an ACC summary of the 2023 ACC/AHA guideline says

  • The summary says the guideline supports estimating stroke risk with a validated score, and it names CHA2DS2-VASc, ATRIA and GARFIELD-AF as examples.27
  • The summary says the guideline favors direct oral anticoagulants over warfarin, with an exception for people who have mitral stenosis or a mechanical heart valve.28
  • The summary says that for people who could take an anticoagulant and have no other reason to take an antiplatelet medicine, the guideline does not recommend aspirin, alone or with clopidogrel, as a stand-in for anticoagulation to lower stroke risk.29
  • The summary says closing off the appendage with a device is reasonable (class 2a, a weaker grade than a full recommendation) for people whose CHA2DS2-VASc score is 2 or more and who have a medical reason not to take anticoagulants over the long term.30
  • It also says closure may reasonably be used in place of anticoagulation (class 2b, weaker still) for people whose stroke risk is moderate or high and who also face a high chance of serious bleeding while taking anticoagulants.30

Topics MedlinePlus raises about taking a blood thinner

  • All of the medicines and supplements in use.17
  • Foods, vitamins and alcohol, which may interact with blood thinners.17
  • Whether regular blood tests are needed to check how well the blood is clotting.17

Questions to ask

  1. How is my risk of stroke with AF estimated, and what does the result mean for my care?
  2. Which kind of blood thinner is being considered for me, and why that one over the others?
  3. What bleeding risk comes with this blood thinner, and how will it be watched for?
  4. Could my foods, other medicines, vitamins, supplements or alcohol interact with a blood thinner?
  5. Will I need regular blood tests to check how well my blood is clotting?
  6. How is aspirin different from the blood thinners used for AF?
  7. Who is a left atrial appendage closure device meant for, and how does that differ from taking a blood thinner?
  8. What risks come with the closure procedure compared with long-term blood thinners?

Sources

  1. Stroke | CVA | Cerebrovascular Accident | MedlinePlus Webpage, MedlinePlus, National Library of Medicine, Summary, What are the symptoms of a stroke?. Retrieved .
  2. Stroke | CVA | Cerebrovascular Accident | MedlinePlus Webpage, MedlinePlus, National Library of Medicine, Summary, What is a stroke?. Retrieved .
  3. Blood Thinners | Anticoagulants (MedlinePlus) Webpage, MedlinePlus, National Library of Medicine, Summary, What are the side effects of blood thinners?. Retrieved .
  4. Atrial Fibrillation | AFib (MedlinePlus) Webpage, MedlinePlus, National Library of Medicine, Summary, What is atrial fibrillation (AFib)?. Retrieved .
  5. Atrial Fibrillation | AFib (MedlinePlus) Webpage, MedlinePlus, National Library of Medicine, Summary, What are the symptoms of atrial fibrillation (AFib)?. Retrieved .
  6. Atrial Fibrillation: What Is Atrial Fibrillation? (NHLBI) Webpage, National Heart, Lung, and Blood Institute (NIH), Page body, paragraph 2. Retrieved .

  7. NHLBI explains that in atrial fibrillation blood can collect in the heart, which makes clots more likely to form, and that clots can cause strokes and other problems. It adds that atrial fibrillation left untreated can have serious, even life-threatening, consequences, and it names stroke and heart failure. MedlinePlus says atrial fibrillation can put a person at risk for stroke and other heart conditions. Neither page gives a number for how much atrial fibrillation raises the risk.

    Applies to Adult
    • People with atrial fibrillation, described in general terms. NHLBI puts the number of US adults with atrial fibrillation above 2 million and says the chance of developing it grows with age. The pages do not describe a study population.
    • Not applicable (patient information pages, not a study)
    • Not stated in the pages for most statements; the prevalence sentence refers to the United States
    • Adults in general. NHLBI describes atrial fibrillation as uncommon in children.
    Follow-up Not applicable (patient information pages)

    Limitations. Patient information pages, not a study. They give no risk estimate and do not say for whom the risk is higher. The NHLBI page is dated 30 November 2022; the MedlinePlus page date was not read.

  8. Atrial Fibrillation | AFib (MedlinePlus) Webpage, MedlinePlus, National Library of Medicine, Summary, What other problems can AFib cause?. Retrieved .
  9. Stroke | CVA | Cerebrovascular Accident | MedlinePlus Webpage, MedlinePlus, National Library of Medicine, Summary, Who is at risk for a stroke?. Retrieved .
  10. Blood Thinners | Anticoagulants (MedlinePlus) Webpage, MedlinePlus, National Library of Medicine, Summary, What are blood thinners?. Retrieved .
  11. Blood Thinners | Anticoagulants (MedlinePlus) Webpage, MedlinePlus, National Library of Medicine, Summary, Who needs blood thinners?. Retrieved .

  12. NHLBI names warfarin and the direct oral anticoagulants (apixaban, dabigatran, rivaroxaban and edoxaban) as medicines that stop clots from forming and so reduce the chance of stroke. It says a person at risk of stroke may need one, and that all of them carry a bleeding risk. MedlinePlus lists atrial fibrillation among the conditions in which a person may need a blood thinner and calls bleeding the most common side effect of blood thinners. Neither page gives a number.

    Applies to Adult
    • People with atrial fibrillation, described in general terms. NHLBI puts the number of US adults with atrial fibrillation above 2 million and says the chance of developing it grows with age. The pages do not describe a study population.
    • Not applicable (patient information pages, not a study)
    • Not stated in the pages for most statements; the prevalence sentence refers to the United States
    • Adults in general. NHLBI describes atrial fibrillation as uncommon in children.
    Follow-up Not applicable (patient information pages)

    Limitations. Patient information pages. They name edoxaban, which has no page in this atlas. The trial results behind apixaban, dabigatran and rivaroxaban are recorded on their own claims, and the pages give no event rates.

  13. Atrial Fibrillation Treatment (NHLBI) Webpage, National Heart, Lung, and Blood Institute (NIH), Page body, Medicines, Blood thinners. Retrieved .
  14. Atrial Fibrillation Treatment (NHLBI) Webpage, National Heart, Lung, and Blood Institute (NIH), Page body, Medicines, Blood thinners (fragment 1 of 2). Retrieved .
  15. Atrial Fibrillation Treatment (NHLBI) Webpage, National Heart, Lung, and Blood Institute (NIH), Page body, Medicines, Blood thinners (fragment 2 of 2). Retrieved .
  16. Blood Thinners | Anticoagulants (MedlinePlus) Webpage, MedlinePlus, National Library of Medicine, Summary, What are the different types of blood thinners?. Retrieved .
  17. Blood Thinners | Anticoagulants (MedlinePlus) Webpage, MedlinePlus, National Library of Medicine, Summary, How can I take blood thinners safely?. Retrieved .
  18. Atrial Fibrillation Treatment (NHLBI) Webpage, National Heart, Lung, and Blood Institute (NIH), Page body, Procedures or surgery (fragment 1 of 2). Retrieved .
  19. Atrial Fibrillation Treatment (NHLBI) Webpage, National Heart, Lung, and Blood Institute (NIH), Page body, Procedures or surgery (fragment 2 of 2). Retrieved .
  20. Percutaneous closure of the left atrial appendage versus warfarin therapy for prevention of stroke in patients with atrial fibrillation: a randomised non-inferiority trial Publication, Journal record via PubMed (Lancet 2009;374(9689):534-42), Abstract, BACKGROUND, sentence 1. Retrieved .

    Source problem. A cited source is corrected. Check the sources before relying on this claim.

  21. Atrial Fibrillation Treatment (NHLBI) Webpage, National Heart, Lung, and Blood Institute (NIH), Page body, Procedures or surgery. Retrieved .

  22. In PROTECT AF, a multicentre, randomised non-inferiority trial, 707 eligible adults with non-valvular atrial fibrillation were randomly assigned 2:1 to percutaneous closure of the left atrial appendage with the WATCHMAN device and subsequent discontinuation of warfarin (463 patients) or to warfarin with a target international normalised ratio of 2.0 to 3.0 (244 patients). Analysis was by intention to treat. At 1065 patient-years of follow-up, the primary efficacy event rate (a composite of stroke, cardiovascular death and systemic embolism) was 3.0 per 100 patient-years (95% credible interval 1.9 to 4.5) in the device group and 4.9 per 100 patient-years (2.8 to 7.1) in the warfarin group (rate ratio 0.62, 95% credible interval 0.35 to 1.25, which includes 1). The probability of non-inferiority was more than 99.9%. Primary safety events (major bleeding, pericardial effusion and device embolisation) were more frequent in the device group, 7.4 per 100 patient-years (95% credible interval 5.5 to 9.7), than in the control group, 4.4 per 100 patient-years (2.5 to 6.7) (rate ratio 1.69, 1.01 to 3.19). The authors write that the safety events in the device group were mainly a result of periprocedural complications.

    Applies to Adult
    • Adults with paroxysmal, persistent or permanent non-valvular atrial fibrillation who were eligible for long-term warfarin and had at least one of: previous stroke or transient ischemic attack, congestive heart failure, diabetes, hypertension, or age 75 or older (abstract wording; the registry gives a CHADS score of 1 or more).
    • Not stated in the abstract or the registry record
    • Registry sites in the United States, Czechia and Germany
    • Adults aged 18 or older (registry minimum age)
    Follow-up The abstract gives 1065 patient-years of follow-up. The registry lists the primary completion as 2013-08.

    Limitations. Abstract of the 2009 report only; the full text was not read. The result is for the first device in the trial, not for later WATCHMAN versions. The intervals are Bayesian 95% credible intervals, and the trial tested non-inferiority with a two-fold margin. The interval for the efficacy rate ratio (0.35 to 1.25) includes 1, so the trial does not show that the device was better than warfarin. Primary safety events were higher with the device (rate ratio 1.69). The trial enrolled people who were eligible for warfarin, so it does not test the device in people who cannot take blood thinners. The abstract names Atritech as funder, while the registry lists Boston Scientific Corporation as lead sponsor; the sources do not explain the difference. PubMed links a published erratum (Lancet 2009 Nov 7;374(9701):1596) and Crossref lists an erratum notice (doi 10.1016/S0140-6736(09)61953-X); neither was read, so the numbers may not match the corrected paper. The registry enrollment (800) includes non-randomized roll-in participants that the abstract does not count among the 707 randomized.

  23. Stroke | CVA | Cerebrovascular Accident | MedlinePlus Webpage, MedlinePlus, National Library of Medicine, Summary, What are the types of stroke?. Retrieved .
  24. Percutaneous closure of the left atrial appendage versus warfarin therapy for prevention of stroke in patients with atrial fibrillation: a randomised non-inferiority trial Publication, Journal record via PubMed (Lancet 2009;374(9689):534-42), Abstract, METHODS, sentence 4. Retrieved .

    Source problem. A cited source is corrected. Check the sources before relying on this claim.

  25. WATCHMAN Left Atrial Appendage System for Embolic PROTECTion in Patients With Atrial Fibrillation (PROTECT AF) Registry, U.S. National Library of Medicine (ClinicalTrials.gov), protocolSection.eligibilityModule.eligibilityCriteria. Retrieved .

  26. The US Food and Drug Administration approved premarket approval application P130013 for the WATCHMAN left atrial appendage closure technology on 13 March 2015, after receiving it on 14 May 2013. The openFDA record names Boston Scientific Corp as applicant and gives product code NGV, device class 3 and an expedited review flag of Y. Its approval-order statement says the device is intended to lower the risk of thromboembolism from the left atrial appendage in people with non-valvular atrial fibrillation who are at increased risk for stroke and systemic embolism by CHADS2 or CHA2DS2-VASC score and are recommended for anticoagulation therapy, who are deemed by their physicians to be suitable for warfarin, and who have an appropriate rationale to seek a non-pharmacologic alternative to warfarin, taking into account how safe and effective the device is compared with warfarin.

    Applies to Recipient not specified
    • People with non-valvular atrial fibrillation who are at increased risk for stroke and systemic embolism based on CHADS2 or CHA2DS2-VASC scores and are recommended for anticoagulation therapy, are deemed by their physicians to be suitable for warfarin, and have an appropriate rationale to seek a non-pharmacologic alternative to warfarin (the wording of the openFDA approval order statement).
    • Not stated in the FDA record
    • United States (decision by the US Food and Drug Administration)
    • Not stated in the FDA record (it says people with non-valvular atrial fibrillation and gives no age)
    • Gestational age Not reported
    • Postnatal age Not reported
    Follow-up Not applicable (regulatory decision)

    Limitations. This is the original approval; the openFDA data hold many later supplements to P130013, including newer device versions, which are not described here. The approval wording ties the device to people who are suitable for warfarin and have a rationale to seek an alternative. It is not a statement that the device is better than warfarin. PROTECT AF tested the first device version. openFDA data are unvalidated.

  27. An ACC summary of the 2023 ACC/AHA atrial fibrillation guideline says the guideline endorses using a validated clinical risk score to estimate stroke and thromboembolism risk; it gives CHA2DS2-VASc, ATRIA and GARFIELD-AF as examples.

    Applies to Recipient not specified
    • Patients with atrial fibrillation. The ACC summary gives no age limits and, apart from the exceptions each claim names, no exclusions.
    • Not stated in the ACC summary.
    • Not stated in the ACC summary (issued by American societies; jurisdiction not verified)
    • Not stated in the ACC summary
    • Gestational age Not reported
    • Postnatal age Not reported
    Follow-up Not applicable (guideline context)

    Limitations. The source is the ACC key-perspectives summary of the guideline (ACC content, hash only), not the guideline text. The summary names three scores as examples and does not rank them. It gives no class of recommendation for this statement. PubMed lists three corrections to the guideline (2024-01-02, 2024-02-27 and 2024-06-11); their text was not read, so it is not known whether they change anything stated here.

  28. An ACC summary of the 2023 ACC/AHA atrial fibrillation guideline says that, apart from patients who have mitral stenosis or a mechanical heart valve, direct oral anticoagulants rather than warfarin are the preferred choice.

    Applies to Recipient not specified
    • Patients with atrial fibrillation. The ACC summary gives no age limits and, apart from the exceptions each claim names, no exclusions.
    • Not stated in the ACC summary.
    • Not stated in the ACC summary (issued by American societies; jurisdiction not verified)
    • Not stated in the ACC summary
    • Gestational age Not reported
    • Postnatal age Not reported
    Follow-up Not applicable (guideline context)

    Limitations. The source is the ACC key-perspectives summary of the guideline (ACC content, hash only), not the guideline text. The summary prints no class of recommendation for this statement and does not say what is preferred in the two exceptions. PubMed lists three corrections to the guideline (2024-01-02, 2024-02-27 and 2024-06-11); their text was not read, so it is not known whether they change anything stated here.

  29. An ACC summary of the 2023 ACC/AHA atrial fibrillation guideline says that for patients who could take an anticoagulant and have no other reason for antiplatelet therapy, aspirin on its own or with clopidogrel is not recommended as a substitute for anticoagulation to lower stroke risk.

    Applies to Recipient not specified
    • Patients with atrial fibrillation. The ACC summary gives no age limits and, apart from the exceptions each claim names, no exclusions.
    • Not stated in the ACC summary.
    • Not stated in the ACC summary (issued by American societies; jurisdiction not verified)
    • Not stated in the ACC summary
    • Gestational age Not reported
    • Postnatal age Not reported
    Follow-up Not applicable (guideline context)

    Limitations. The source is the ACC key-perspectives summary of the guideline (ACC content, hash only), not the guideline text. The summary prints no class of recommendation for this statement. It speaks of patients who could take an anticoagulant; it does not address people who cannot take one. PubMed lists three corrections to the guideline (2024-01-02, 2024-02-27 and 2024-06-11); their text was not read, so it is not known whether they change anything stated here.

  30. An ACC summary of the 2023 ACC/AHA atrial fibrillation guideline says percutaneous left atrial appendage occlusion is reasonable (class 2a) for patients with a CHA2DS2-VASc score of 2 or more who have a medical reason not to take anticoagulants over the long term, and might reasonably be used instead of anticoagulation (class 2b) for patients at moderate or high stroke risk who also face a high chance of serious bleeding while taking anticoagulants.

    Applies to Recipient not specified
    • Patients with atrial fibrillation. The ACC summary gives no age limits and, apart from the exceptions each claim names, no exclusions.
    • Not stated in the ACC summary.
    • Not stated in the ACC summary (issued by American societies; jurisdiction not verified)
    • Not stated in the ACC summary
    • Gestational age Not reported
    • Postnatal age Not reported
    Follow-up Not applicable (guideline context)

    Limitations. The source is the ACC key-perspectives summary of the guideline (ACC content, hash only), not the guideline text. The classes of recommendation are as printed on the ACC page. These are weaker recommendations than a plain recommendation, so no recommendation record is written for them. PubMed lists three corrections to the guideline (2024-01-02, 2024-02-27 and 2024-06-11); their text was not read, so it is not known whether they change anything stated here.

About this guide

Written for
Adults with atrial fibrillation, and the people with them
What it covers
Written from three MedlinePlus health topic pages, two NHLBI pages, an ACC summary of a guideline, a 2009 trial abstract, a trial registry entry and a US FDA approval record. The NHLBI and ACC wording is restated in the atlas’s own words. It describes what these sources say and gives no advice for one person. It leaves out doses and the results of the trials that compared single blood thinners.
Pages it explains
Sources checked
2026-10-15
Next check due
2027-04-15
Reading level
Estimated grade 8.8 (target 9)

Every sentence cites a source. Words in quotation marks are the source's own; the rest is the atlas's summary.

https://cardio.openmedicalatlas.org/guides/afib-blood-thinners/ · Release f4600233112e1c27, built 2026-10-15