# My watch flagged an irregular rhythm Guide · id `cardio:guide-watch-irregular-rhythm` · Cardiovascular Atlas · release `f4600233112e1c27` (public) > General information only. This guide shows what the sources it cites say. It is not medical advice, it cannot tell you what is right for you, and no clinician has reviewed it. Talk to a qualified health professional about your own care. In an emergency, call your local emergency number. > General information from published sources, not medical advice, and not reviewed by clinicians. Check the cited source before relying on anything here. The atlas's own text and curation may be reused under Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0, https://creativecommons.org/licenses/by-nc/4.0/): credit the atlas, and do not use it commercially. See the atlas About page. Text quoted from a source stays under that source's own terms, given as the source's reuse\_basis. The atlas's reuse terms do not cover it. The downloads list each quotation with its source in third\_party\_quotations. What FDA's 2018 summary says one watch feature is for, what studies of watch alerts measured, how the sources describe checking for atrial fibrillation, and questions to ask a clinician. ## Signs the sources say need care: From the MedlinePlus arrhythmia page - MedlinePlus lists chest pain among the symptoms of an arrhythmia. [1] - MedlinePlus also lists shortness of breath among the symptoms of an arrhythmia. [2] > “Seek emergency medical care if you have chest pain, shortness of breath, or think you are having a heart attack.” [3] > > — MedlinePlus, National Library of Medicine, Arrhythmia | Irregular Heartbeat (MedlinePlus) In an emergency, call your local emergency number. ## What FDA's 2018 summary says about the feature - FDA granted a De Novo request from Apple for software that sends irregular rhythm notifications on the Apple Watch, with a decision date of September 11, 2018. [4, 5, 6] - The summary says the Apple Watch software studies pulse data and sends a notification, here called an alert, when it spots an irregular rhythm that may point to atrial fibrillation (AFib). [7, 8] - It labels the feature as over-the-counter. [9] - It calls the feature a tool that screens in the background and says a user cannot start a check. [10] - It says the data are captured only while the wearer is still. [11] - In this 2018 description, an alert appears when five of six readings in a row, within 48 hours, are classified as irregular. [12] - The summary says the alert also encourages users who were not previously diagnosed with AFib to seek medical care. [13] - It says the phone app shows a record of past AFib alerts and a list of when the irregular readings behind each one were taken. [14, 15] - It says the feature was not tested in people under 22, and that it is not meant for them or for people previously diagnosed with AFib. [16, 17] - It adds that the feature, together with a person's risk factors, can help inform the decision about AFib screening. [18] - It says the feature is not meant to replace usual diagnosis or treatment, and not meant to guide clinical care. [19, 20] - FDA's description of this type of device adds that such a device is not meant to diagnose. [21] ## What the 2018 summary says an alert cannot tell - The labeling text in the summary calls an alert a possible finding, not a full diagnosis of heart conditions. [22] - That text also says a medical professional should review all alerts. [23] - The summary also says the labeling states that an AFib diagnosis should still rest on confirmation by ECG. [24] - The summary says the feature is not meant to give an alert for every irregular episode, and a missing alert is not meant to show that no disease is present. [25] - The labeling text says the feature does not look for AFib all the time, so it cannot find every instance and some people with AFib may get no alert. [26, 27] - The labeling text also says the feature is unable to detect a heart attack. [28] - The labeling text lists motion, hand and finger movement, dark wrist tattoos, and blood flow to the skin, which cold can reduce, among factors that can affect the pulse measurement. [29, 30] - The summary names a probable risk that users will misread the output and ignore acute symptoms, such as those of a heart attack. [31] - It also says users may take the output as permission to avoid following a treatment already prescribed for a long-term heart condition. [31] ## What studies of watch alerts measured - The Apple Heart Study used its own research app, and this guide's sources do not say how that app, or the study, relates to the clinical study in the FDA summary. [32] - The Apple Heart Study recruited 419,297 people who reported having no atrial fibrillation, and a smartwatch program looked for an irregular pulse. [33, 34, 35] - Over a median of 117 days of monitoring, 2161 people (0.52%) received a notification of an irregular pulse from the study's app. [36, 37] - Of the 450 notified people who returned usable ECG patch data, 34% (97.5% confidence interval, 29 to 39) had atrial fibrillation on the patch, which was applied on average 13 days after the notification. [37, 38, 39] - Of 1376 people who got a notification from the study's app and returned a 90-day survey, 57% contacted health care providers outside the study. [40] - The study's registry entry lists a single study group. [41] - Its registry entry lists four outcomes, about atrial fibrillation of more than 30 seconds, confirmed atrial fibrillation, agreement with the app's notification, and contact with a health care provider. [42, 43, 44, 45] - None of the four outcomes is about strokes. [42, 43, 44, 45] - In a sub-study described in the FDA summary, the result for single irregular readings did not reach the accuracy goal set before the study. [46] - FDA still judged the secondary and further analyses to support the feature's effectiveness in detecting AFib. [47] - In an analysis added after the study's plan, of 226 people who already had notifications from the feature, AFib was documented on later 7-day patch monitoring in 41.6% (95% CI, 35.1 to 48.3). [48] - FDA wrote that this feature is not meant to diagnose AFib but is an accessible tool for finding people who would probably gain from more AFib screening using ECG-based methods. [49] ## How the sources describe checking for atrial fibrillation - MedlinePlus says some people who have AFib have no symptoms and do not know they have it. [50] - MedlinePlus says AFib may happen in brief episodes, or it may be a permanent condition. [51] - NHLBI says a provider reaches a diagnosis of atrial fibrillation using the patient's history and a physical exam, along with an EKG and, in some cases, other tests. [52] - NHLBI says an EKG records the electrical activity of the heart. [53] - NHLBI says Holter and event monitors are portable EKG devices that record over long periods of everyday activity. [54] - It says they can help explain symptoms such as palpitations or dizziness that occur away from the provider's office. [54] - NHLBI also says that several devices can now detect and record heart rhythm in a way similar to an EKG, and that readings from these devices may be emailed to a provider. [55] - MedlinePlus says a provider will ask about medical history, including symptoms, lifestyle and other health conditions, and about relatives who have or had AFib. [56, 57] - MedlinePlus says a provider will likely order heart tests such as an electrocardiogram (“also called an EKG or ECG”) and an echocardiogram, and may ask the patient to wear a heart monitor. [58, 59] ## What MedlinePlus lists as symptoms of an arrhythmia - MedlinePlus says symptoms of arrhythmias in general can include a fast or slow heartbeat; skipping, fluttering or pounding heartbeats; chest pain or discomfort; dizziness or fainting; shortness of breath; sweating; and tiredness or weakness. [1, 2, 60, 61, 62, 63, 64, 65] ## What a national task force said about screening - In 2022, the USPSTF found the evidence too limited to judge whether screening for atrial fibrillation does more good than harm, which it calls an I statement. [66] - The statement covers adults 50 or older with no atrial fibrillation diagnosis or symptoms and no earlier stroke or transient ischemic attack. [66] ## What the sources say a provider asks about or uses - [ ] A record of how often and when symptoms occur, what is felt and whether this changes over time, which NHLBI calls important clues for diagnosis. [67, 68] - [ ] Heart rhythm readings from a device, which NHLBI says may be emailed to a provider. [55] - [ ] Medical history, including symptoms, lifestyle and other health conditions, which MedlinePlus says a provider will ask about. [56] - [ ] Family history of AFib, which MedlinePlus says a provider will ask about. [57] ## Questions to ask 1. Does my watch alert point to atrial fibrillation, and which test would confirm it? 2. The FDA summary says the feature is not meant for people under 22 or people already diagnosed with AFib; does that apply to me? 3. If my watch gives no alert, does that say anything about my heart? 4. Would an EKG, a heart monitor or another test help sort out what the alert found? 5. Would the history of alerts on my phone, or a record of my symptoms, help you? 6. Can readings from my device be sent to you, and in what form? 7. Do the results of the Apple Heart Study apply to someone like me? 8. Does the 2022 task force statement on screening change anything for me? ## Sources 1. Arrhythmia | Irregular Heartbeat (MedlinePlus) (Webpage, MedlinePlus, National Library of Medicine) . Locator: Summary, What are the symptoms of an arrhythmia?, list item 3. Retrieved 2026-10-14. 2. Arrhythmia | Irregular Heartbeat (MedlinePlus) (Webpage, MedlinePlus, National Library of Medicine) . Locator: Summary, What are the symptoms of an arrhythmia?, list item 5. Retrieved 2026-10-14. 3. Arrhythmia | Irregular Heartbeat (MedlinePlus) (Webpage, MedlinePlus, National Library of Medicine) . Locator: Summary, What are the symptoms of an arrhythmia?, last sentence. Retrieved 2026-10-14. 4. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Conclusion. Retrieved 2026-10-15. 5. FDA De Novo DEN180042: Irregular Rhythm Notification Feature (openFDA record) (Regulator, U.S. Food and Drug Administration (openFDA)) . Locator: results\[0\].decision\_date. Retrieved 2026-10-14. 6. FDA De Novo DEN180042: Irregular Rhythm Notification Feature (openFDA record) (Regulator, U.S. Food and Drug Administration (openFDA)) . Locator: results\[0\].applicant. Retrieved 2026-10-14. 7. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Indications for use, sentence 1. Retrieved 2026-10-15. 8. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Indications for use, sentence 2. Retrieved 2026-10-15. 9. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Indications for use, sentence 3. Retrieved 2026-10-15. 10. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Device description, paragraph 1. Retrieved 2026-10-15. 11. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Indications for use, sentence 5. Retrieved 2026-10-15. 12. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Device description, Irregular Rhythm Notification Feature, sentence 2. Retrieved 2026-10-15. 13. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Device description, Irregular Rhythm Notification Feature, last sentence. Retrieved 2026-10-15. 14. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Device description, iPhone App, sentence 3. Retrieved 2026-10-15. 15. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Device description, iPhone App, sentence 4. Retrieved 2026-10-15. 16. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Indications for use, paragraph 2, sentence 1. Retrieved 2026-10-15. 17. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Indications for use, paragraph 2, sentence 2. Retrieved 2026-10-15. 18. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Indications for use, sentence 6. Retrieved 2026-10-15. 19. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Indications for use, sentence 7. Retrieved 2026-10-15. 20. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Device description, paragraph 2. Retrieved 2026-10-15. 21. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Regulatory information, device type. Retrieved 2026-10-15. 22. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Limitations, notifications paragraph, sentence 1. Retrieved 2026-10-15. 23. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Limitations, notifications paragraph, sentence 2. Retrieved 2026-10-15. 24. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Benefit/risk determination, paragraph 2. Retrieved 2026-10-15. 25. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Indications for use, sentence 4. Retrieved 2026-10-15. 26. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Limitations, paragraph 2, sentence 1. Retrieved 2026-10-15. 27. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Limitations, paragraph 2, sentence 2. Retrieved 2026-10-15. 28. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Limitations, paragraph 1. Retrieved 2026-10-15. 29. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Limitations, paragraph 4, sentence 1. Retrieved 2026-10-15. 30. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Limitations, paragraph 4, sentence 2. Retrieved 2026-10-15. 31. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Benefit/risk determination, paragraph 3. Retrieved 2026-10-15. 32. Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias (Registry, U.S. National Library of Medicine (ClinicalTrials.gov)) . Locator: protocolSection.armsInterventionsModule.armGroups\[0\].label. Retrieved 2026-10-14. 33. Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, RESULTS, sentence 1. Retrieved 2026-10-14. 34. Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, METHODS, sentence 1. Retrieved 2026-10-14. 35. Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, METHODS, sentence 2, fragment 1 of 2. Retrieved 2026-10-14. 36. Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, RESULTS, sentence 2. Retrieved 2026-10-14. 37. Claim `cardio:claim-apple-heart-study-alerts`: In the Apple Heart Study, 419,297 participants with no self-reported atrial fibrillation used an Apple Watch and iPhone app, and were followed for a median of 117 days. 2161 of them (0.52%) received a notification of an irregular pulse. Of the 450 notified participants who returned ECG patches with data that could be analyzed (applied on average 13 days after the notification), 34% had atrial fibrillation on the patch (97.5% confidence interval 29 to 39), and 35% of those aged 65 or older (97.5% CI 27 to 43). Separately, the positive predictive value among notified participants was 0.84 (95% CI 0.76 to 0.92) for atrial fibrillation on the ECG at the same time as a later irregular pulse notification, and 0.71 (97.5% CI 0.69 to 0.74) for atrial fibrillation on the ECG at the same time as an irregular tachogram. Of 1376 notified participants who returned a 90-day survey, 57% contacted health care providers outside the study. The paper reports no serious app-related adverse events. - Applies to: People aged 22 or older who lived in the United States, owned a compatible iPhone and Apple Watch, had no self-reported diagnosis of atrial fibrillation or atrial flutter, and were not on anticoagulation therapy (registry exclusion criteria).; Remote and siteless. People consented and took part through a smartphone app with no on-site visits. After a notification, the study started a telemedicine visit and mailed an ECG patch to the participant.; United States (the registry lists only the United States as a country); Adults aged 22 or older (registry minimum age). The abstract reports one result separately for participants aged 65 or older.. Follow-up: Median of 117 days of monitoring. An ECG patch was worn for up to 7 days (the registry gives up to 8 days of ambulatory monitoring) and was applied on average 13 days after a notification. Surveys were sent 90 days after a notification and at the end of the study. - Limitations: Single-group study with no comparison group, using the study's own research app. The result is not about the FDA-authorized feature itself, and the sources read do not say how the two relate. The registry lists as outcomes the share of notified participants with AF on the ECG, agreement between the app and the ECG, and contact with a health care provider. It lists no stroke or other clinical outcome, so the study does not show that notifications prevent strokes. Only 450 of the 2161 notified participants returned analyzable patches. The abstract gives the 34% (97.5% CI) and the 0.84 (95% CI) as separate measures, and they are not the same quantity. The registry enrollment (419927) and the abstract recruitment count (419,297) differ and are not reconciled. Participants were self-selected owners of a compatible phone and watch, and the abstract does not describe their health or demographics. Abstract only; the PMC copy is not in the Open Access subset and the full text was not read. - Supports: Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, RESULTS, sentence 1. Retrieved 2026-10-14. - Supports: Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, RESULTS, sentence 2. Retrieved 2026-10-14. - Supports: Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, RESULTS, sentence 3, fragment 1. Retrieved 2026-10-14. - Supports: Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, RESULTS, sentence 3, fragment 2. Retrieved 2026-10-14. - Supports: Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, RESULTS, sentence 3, fragment 3. Retrieved 2026-10-14. - Supports: Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, RESULTS, sentence 4, fragment 1. Retrieved 2026-10-14. - Supports: Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, RESULTS, sentence 4, fragment 2. Retrieved 2026-10-14. - Supports: Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, RESULTS, sentence 4, fragment 3. Retrieved 2026-10-14. - Supports: Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, RESULTS, sentence 5. Retrieved 2026-10-14. - Supports: Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, RESULTS, sentence 6. Retrieved 2026-10-14. - Supports: Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, CONCLUSIONS, sentence 1. Retrieved 2026-10-14. - Background: Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, METHODS, sentence 4, fragment 1. Retrieved 2026-10-14. - Background: Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias (Registry, U.S. National Library of Medicine (ClinicalTrials.gov)) . Locator: protocolSection.outcomesModule.primaryOutcomes\[0\].measure. Retrieved 2026-10-14. - Background: Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias (Registry, U.S. National Library of Medicine (ClinicalTrials.gov)) . Locator: protocolSection.outcomesModule.primaryOutcomes\[1\].measure. Retrieved 2026-10-14. - Background: Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias (Registry, U.S. National Library of Medicine (ClinicalTrials.gov)) . Locator: protocolSection.outcomesModule.secondaryOutcomes\[0\].measure. Retrieved 2026-10-14. - Background: Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias (Registry, U.S. National Library of Medicine (ClinicalTrials.gov)) . Locator: protocolSection.outcomesModule.secondaryOutcomes\[1\].measure. Retrieved 2026-10-14. - Background: Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias (Registry, U.S. National Library of Medicine (ClinicalTrials.gov)) . Locator: protocolSection.designModule.enrollmentInfo.count. Retrieved 2026-10-14. 38. Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, RESULTS, sentence 3, fragment 1 of 3. Retrieved 2026-10-14. 39. Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, RESULTS, sentence 3, fragment 2 of 3. Retrieved 2026-10-14. 40. Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation (Publication, Massachusetts Medical Society (N Engl J Med 2019;381(20):1909-1917), via PubMed) . Locator: Abstract, RESULTS, sentence 5. Retrieved 2026-10-14. 41. Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias (Registry, U.S. National Library of Medicine (ClinicalTrials.gov)) . Locator: protocolSection.designModule.designInfo.interventionModel. Retrieved 2026-10-14. 42. Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias (Registry, U.S. National Library of Medicine (ClinicalTrials.gov)) . Locator: protocolSection.outcomesModule.primaryOutcomes\[0\].measure. Retrieved 2026-10-14. 43. Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias (Registry, U.S. National Library of Medicine (ClinicalTrials.gov)) . Locator: protocolSection.outcomesModule.primaryOutcomes\[1\].measure. Retrieved 2026-10-14. 44. Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias (Registry, U.S. National Library of Medicine (ClinicalTrials.gov)) . Locator: protocolSection.outcomesModule.secondaryOutcomes\[0\].measure. Retrieved 2026-10-14. 45. Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias (Registry, U.S. National Library of Medicine (ClinicalTrials.gov)) . Locator: protocolSection.outcomesModule.secondaryOutcomes\[1\].measure. Retrieved 2026-10-14. 46. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Summary of clinical study, performance results. Retrieved 2026-10-15. 47. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Summary of clinical study, secondary analyses. Retrieved 2026-10-15. 48. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Summary of clinical study, post hoc analysis. Retrieved 2026-10-15. 49. De Novo Classification Request for Irregular Rhythm Notification Feature (FDA decision summary, DEN180042) (Regulator, U.S. Food and Drug Administration) . Locator: Benefit/risk determination, paragraph 1. Retrieved 2026-10-15. 50. Atrial Fibrillation | AFib (MedlinePlus) (Webpage, MedlinePlus, National Library of Medicine) . Locator: Summary, What are the symptoms of atrial fibrillation (AFib)?, sentence 1. Retrieved 2026-10-14. 51. Atrial Fibrillation | AFib (MedlinePlus) (Webpage, MedlinePlus, National Library of Medicine) . Locator: Summary, What is atrial fibrillation (AFib)?, para 3. Retrieved 2026-10-14. 52. Atrial Fibrillation Diagnosis (NHLBI) (Webpage, National Heart, Lung, and Blood Institute (NIH)) . Locator: Page body, introduction. Retrieved 2026-10-15. 53. Atrial Fibrillation Diagnosis (NHLBI) (Webpage, National Heart, Lung, and Blood Institute (NIH)) . Locator: Page body, Diagnostic tests, bullet 1. Retrieved 2026-10-15. 54. Atrial Fibrillation Diagnosis (NHLBI) (Webpage, National Heart, Lung, and Blood Institute (NIH)) . Locator: Page body, Other tests, Holter and event monitors. Retrieved 2026-10-15. 55. Atrial Fibrillation Diagnosis (NHLBI) (Webpage, National Heart, Lung, and Blood Institute (NIH)) . Locator: Page body, Screening methods, bullet 2. Retrieved 2026-10-15. 56. Atrial Fibrillation | AFib (MedlinePlus) (Webpage, MedlinePlus, National Library of Medicine) . Locator: Summary, How is atrial fibrillation (AFib) diagnosed?, list item 1. Retrieved 2026-10-14. 57. Atrial Fibrillation | AFib (MedlinePlus) (Webpage, MedlinePlus, National Library of Medicine) . Locator: Summary, How is atrial fibrillation (AFib) diagnosed?, list item 2. Retrieved 2026-10-14. 58. Atrial Fibrillation | AFib (MedlinePlus) (Webpage, MedlinePlus, National Library of Medicine) . Locator: Summary, How is atrial fibrillation (AFib) diagnosed?, list item 5. Retrieved 2026-10-14. 59. Atrial Fibrillation | AFib (MedlinePlus) (Webpage, MedlinePlus, National Library of Medicine) . Locator: Summary, How is atrial fibrillation (AFib) diagnosed?, list item 6. Retrieved 2026-10-14. 60. Arrhythmia | Irregular Heartbeat (MedlinePlus) (Webpage, MedlinePlus, National Library of Medicine) . Locator: Summary, What are the symptoms of an arrhythmia?, lead-in. Retrieved 2026-10-14. 61. Arrhythmia | Irregular Heartbeat (MedlinePlus) (Webpage, MedlinePlus, National Library of Medicine) . Locator: Summary, What are the symptoms of an arrhythmia?, list item 1. Retrieved 2026-10-14. 62. Arrhythmia | Irregular Heartbeat (MedlinePlus) (Webpage, MedlinePlus, National Library of Medicine) . Locator: Summary, What are the symptoms of an arrhythmia?, list item 2. Retrieved 2026-10-14. 63. Arrhythmia | Irregular Heartbeat (MedlinePlus) (Webpage, MedlinePlus, National Library of Medicine) . Locator: Summary, What are the symptoms of an arrhythmia?, list item 4. Retrieved 2026-10-14. 64. Arrhythmia | Irregular Heartbeat (MedlinePlus) (Webpage, MedlinePlus, National Library of Medicine) . Locator: Summary, What are the symptoms of an arrhythmia?, list item 6. Retrieved 2026-10-14. 65. Arrhythmia | Irregular Heartbeat (MedlinePlus) (Webpage, MedlinePlus, National Library of Medicine) . Locator: Summary, What are the symptoms of an arrhythmia?, list item 7. Retrieved 2026-10-14. 66. Claim `cardio:claim-uspstf-2022-af-screening-i`: For asymptomatic adults aged 50 or older, the USPSTF finds the evidence now available too limited to judge whether screening for atrial fibrillation does more good than harm (an I statement). The abstract says evidence is lacking, so the balance cannot be determined. - Applies to: Adults aged 50 or older with no diagnosis or symptoms of atrial fibrillation and no earlier transient ischemic attack or stroke, as the abstract defines the population. The abstract describes the recommendation as concerning asymptomatic adults.; Not stated in the abstract.; United States (a USPSTF recommendation); Adults aged 50 or older. Follow-up: Not applicable (guideline context) - Limitations: An I statement means the evidence is too thin to support a recommendation either way. It is not advice against screening, and it does not say that screening finds nothing or that anticoagulation does not help. The statement updates a 2018 recommendation. Only the PubMed abstract and the date line of the USPSTF page were read. No recommendation record is written, because this atlas has no record for atrial fibrillation screening itself. - Supports: Screening for Atrial Fibrillation: US Preventive Services Task Force Recommendation Statement (Guideline, JAMA) . Locator: Abstract, RECOMMENDATION, sentence 1. Retrieved 2026-10-15. - Supports: Screening for Atrial Fibrillation: US Preventive Services Task Force Recommendation Statement (Guideline, JAMA) . Locator: Abstract, RECOMMENDATION, sentence 2. Retrieved 2026-10-15. - Supports: Screening for Atrial Fibrillation: US Preventive Services Task Force Recommendation Statement (Guideline, JAMA) . Locator: Abstract, EVIDENCE ASSESSMENT, sentence 1. Retrieved 2026-10-15. - Background: Screening for Atrial Fibrillation: US Preventive Services Task Force Recommendation Statement (Guideline, JAMA) . Locator: Abstract, POPULATION, sentence 1. Retrieved 2026-10-15. - Background: Screening for Atrial Fibrillation: US Preventive Services Task Force Recommendation Statement (Guideline, JAMA) . Locator: Page header, date line of the final recommendation statement. Retrieved 2026-10-15. 67. Atrial Fibrillation Symptoms (NHLBI) (Webpage, National Heart, Lung, and Blood Institute (NIH)) . Locator: Page body, after the symptom list, sentence 1. Retrieved 2026-10-15. 68. Atrial Fibrillation Symptoms (NHLBI) (Webpage, National Heart, Lung, and Blood Institute (NIH)) . Locator: Page body, after the symptom list, sentence 2. Retrieved 2026-10-15. ## About this guide - Written for: Adults whose smartwatch has flagged an irregular rhythm, and the people with them - What it covers: Written from an FDA summary, a study abstract, a registry entry, a task force statement and four US government health pages. The FDA summary covers one 2018 authorization, for Apple's feature. Other watches and later versions of the feature are not covered. The guide describes what the sources say. It gives no advice for one person. - Pages it explains: Irregular Rhythm Notification Feature (Apple) (`cardio:apple-irregular-rhythm-notification`); Smartwatch irregular-pulse detection (`cardio:wearable-rhythm-detection`); Apple Heart Study (`cardio:apple-heart-study`); USPSTF 2022: screening for atrial fibrillation (`cardio:guideline-uspstf-2022-af-screening`); Atrial fibrillation (AF) (`cardio:atrial-fibrillation`) - Sources checked: 2026-10-15 - Next check due: 2027-04-15 - Estimated reading grade: 9.9 (target 10) Every sentence cites a source. Words in quotation marks are the source's own; the rest is the atlas's summary. ## Provenance Content hash: ae13f7bcd486ce489bdca88e333dd7d10e3cda8d83059aee1293ccd69348eefe Last substantive edit: 2026-10-15 Evidence last checked: 2026-10-15