Editorials

Downsides of Detecting Atrial Fibrillation in Asymptomatic Patients

 

Am Fam Physician. 2019 Mar 15;99(6):354-355.

Related Putting Prevention into Practice: Screening for Atrial Fibrillation with Electrocardiography

Related U.S. Preventive Services Task Force Recommendation Statement: Screening for Atrial Fibrillation with Electrocardiography: Recommendation Statement

The rise in the number of people who are obese and the fact that people live longer and with more comorbid conditions have led to an increase in the prevalence of atrial fibrillation (AF), a condition associated with stroke and heart failure.1,2 AF is often asymptomatic. Oral anticoagulants are an accepted therapy for selected patients with AF. These factors have led some physicians to promote screening for AF.3 The proliferation of devices capable of recording the heart rhythm has further increased enthusiasm for early detection.

Although early detection of disease has appeal, screening for AF presents several practical challenges.4 These include low overall prevalence in the screened population, excess costs, poor specificity of tests for AF, harms from misdiagnosis and overtreatment, and lack of understanding of the natural history of screen-detected AF. The U.S. Preventive Services Task Force recently concluded that current evidence is insufficient to assess the balance of benefits and harms of screening for AF with electrocardiography (ECG).5

The Swedish STROKESTOP study illustrates the problem of low prevalence.6 Using intermittent ECG recordings in more than 7,000 people 75 or 76 years of age, the authors found new AF on the initial ECG in 0.5% of the screened group. Thus, in this ideal population, the number needed to screen (NNS) to detect one person with AF is 200. Assuming an absolute stroke risk reduction of 2% with oral anticoagulants (number needed to treat = 50), the NNS to prevent one stroke is 10,000. In younger populations with a lower prevalence of AF, the NNS would be substantially higher.

The cost of screening that many people to prevent one event will likely exceed the cost of treating patients with stroke. For example, at an estimated ECG price of $40 (reasonable fair price; https://healthcarebluebook.com/) and a yearly oral anticoagulant price of $100, it would cost $1.4 million ([40 + 100] × 10,000 NNS) to prevent one stroke in people older than 75 years. Given a more realistic cost of $500 yearly (or more) for newer anticoagulants, the cost then increases to $5.5 million to prevent one stroke. That cost is further increased by downstream effects of medical care for true- and false-positive diagnoses of AF plus any incidental ECG findings (e.g., premature ventricular contractions).

The specificity of a test measures its ability to correctly identify those without the disease. The British Screening for Atrial Fibrillation in the Elderly (SAFE) study reported a 90% specificity for ECG findings obtained by general practitioners or nurses.7 False-positive rates of 10% or more have been confirmed with computer reads of 12-lead ECGs,8,9 the iPhone ECG,10 and artificial intelligence–enhanced smart-watch detection of AF.11 Screening with pulse palpation has a far lower specificity of 70% to 77%.12 Causes of false-positive AF recordings include premature atrial contractions, premature ventricular contractions, atrial tachycardias, and, most commonly, unrecognized baseline artifact.

People can now have their heart rhythms recorded with an ECG rhythm-strip app on the Apple Watch. If we assume a screened population of 10 million watch owners, a 90% specificity for the recording, and a generous estimate of AF prevalence of 2%, 200,000 people will have AF and 9,800,000 will not. Multiplying the 10% false-positive rate by the 9.8 million people without AF leads to a misdiagnosis of AF in nearly 1 million people for every 10 million screened. If millions seek medical treatment, that would lead to iatrogenic harm from complications of diagnostic testing, bleeding from unnecessary anticoagulation, and anxiety from having a cardiac diagnosis. The prevalence of AF in the population of watch users is likely to be far lower than that in medical studies involving older individuals, such as those in the STROKESTOP study.

To date, no study of AF screening has measured outcomes. We know that AF screening leads to higher rates of detection, office visits, and prescriptions for anticoagulants.13 Even if screening could be restricted to higher risk individuals, it is not clear that this would lead to better outcomes.

Despite decades of research, the natural history of AF remains poorly understood. Whereas epidemiologic studies find that AF is associated with stroke, links between AF and stroke fail to fulfill many of Hill's criteria for causation.14 AF does not fit the temporality criteria15; it fails in the specificity criteria because many strokes in patients with AF stem from vascular disease rather than cardiac emboli16; and it fails the accordance with evidence criteria17 suggesting that rhythm-control drugs would reduce stroke risk, which they do not.18

Another knowledge deficit is the uncertainty surrounding untreated stroke risks. A systematic review of patients with AF who were not treated with anticoagulants found a large variation in stroke risk, ranging from 0.4% to 9.3% per year, which persisted across any single CHA2DS2-VASc (congestive heart failure; hypertension; age 75 years or older [doubled]; diabetes mellitus; prior stroke, transient ischemic attack, or thromboembolism [doubled]; vascular disease; age 65 to 74 years; sex category) score.19 This is problematic because if the untreated stroke risk is not known, it is difficult to calculate the net benefits of anticoagulation.20

Finally, the evidence underpinning anticoagulation stems from trials in the 1990s involving patients with symptomatic AF. Given the decline in stroke rates, improvements in acute stroke care, and current use of devices capable of detecting seconds of AF, it is not known whether anticoagulant medications will deliver net benefit for screen-detected AF or at what threshold to begin therapy. Ongoing trials are studying the use of direct-acting oral anticoagulants vs. aspirin for device-detected subclinical AF.20

Despite the lack of outcomes evidence, the rise of wearable ECG sensors will cause many individuals to seek care for misdiagnosed AF. People with false-positive results will require only reassurance. The best intervention for patients with correct diagnoses remains unclear. Primary care physicians must use their skills in discussing uncertainty and aligning care with patients' goals.

Address correspondence to John Mandrola, MD, at john.mandrola@gmail.com. Reprints are not available from the authors.

Author disclosure: No relevant financial affiliations.

References

show all references

1. Lane DA, Skjøth F, Lip GY, Larsen TB, Kotecha D. Temporal trends in incidence, prevalence, and mortality of atrial fibrillation in primary care. J Am Heart Assoc. 2017;6(5):e005155....

2. Foy AJ, Mandrola J, Liu G, Naccarelli GV. Relation of obesity to new-onset atrial fibrillation and atrial flutter in adults. Am J Cardiol. 2018;121(9):1072–1075.

3. Freedman B, Camm J, Calkins H, et al.; AF-Screen Collaborators. Screening for atrial fibrillation: a report of the AF-SCREEN International Collaboration. Circulation. 2017;135(19):1851–1867.

4. Mandrola J, Foy A, Naccarelli G. Screening for atrial fibrillation comes with many snags. JAMA Intern Med. 2018;178(10):1296–1298.

5. Curry SJ, Krist AH, Owens DK, et al. Screening for atrial fibrillation with electrocardiography: U.S. Preventive Services Task Force recommendation statement. JAMA. 2018;320(5):478–484.

6. Svennberg E, Engdahl J, Al-Khalili F, Friberg L, Frykman V, Rosenqvist M. Mass screening for untreated atrial fibrillation: the STROKESTOP study. Circulation. 2015;131(25):2176–2184.

7. Mant J, Hobbs FD, Fletcher K, et al.; BAFTA Investigators; Midland Research Practices Network. Warfarin versus aspirin for stroke prevention in an elderly community population with atrial fibrillation (the Birmingham Atrial Fibrillation Treatment of the Aged Study, BAFTA): a randomised controlled trial. Lancet. 2007;370(9586):493–503.

8. Hwan Bae M, Hoon Lee J, Heon Yang D, et al. Erroneous computer electrocardiogram interpretation of atrial fibrillation and its clinical consequences. Clin Cardiol. 2012;35(6):348–353.

9. Bogun F, Anh D, Kalahasty G, et al. Misdiagnosis of atrial fibrillation and its clinical consequences. Am J Med. 2004;117(9):636–642.

10. Lowres N, Neubeck L, Salkeld G, et al. Feasibility and cost-effectiveness of stroke prevention through community screening for atrial fibrillation using iPhone ECG in pharmacies. The SEARCH-AF study. Thromb Haemost. 2014;111(6):1167–1176.

11. Tison GH, Sanchez JM, Ballinger B, et al. Passive detection of atrial fibrillation using a commercially available smartwatch. JAMA Cardiol. 2018;3(5):409–416.

12. Cooke G, Doust J, Sanders S. Is pulse palpation helpful in detecting atrial fibrillation? A systematic review. J Fam Pract. 2006;55(2):130–134.

13. Steinhubl SR, Waalen J, Edwards AM, et al. Effect of a home-based wearable continuous ECG monitoring patch on detection of undiag-nosed atrial fibrillation: the mSToPS randomized clinical trial. JAMA. 2018;320(2):146–155.

14. Kamel H, Okin PM, Elkind MS, Iadecola C. Atrial fibrillation and mechanisms of stroke: time for a new model. Stroke. 2016;47(3):895–900.

15. Daoud EG, Glotzer TV, Wyse DG, et al. Temporal relationship of atrial tachyarrhythmias, cerebrovascular events, and systemic emboli based on stored device data: a subgroup analysis of TRENDS. Heart Rhythm. 2011;8(9):1416–1423.

16. Lodder J, Bamford JM, Sandercock PA, Jones LN, Warlow CP. Are hypertension or cardiac embolism likely causes of lacunar infarction? Stroke. 1990;21(3):375–381.

17. Hill AB. The environment and disease: association or causation? Proc R Soc Med. 1965;58:295–300.

18. Al-Khatib SM, Allen LaPointe NM, Chatterjee R, et al. Rate- and rhythm-control therapies in patients with atrial fibrillation: a systematic review. Ann Intern Med. 2014;160(11):760–773.

19. Quinn GR, Severdija ON, Chang Y, Singer DE. Wide variation in reported rates of stroke across cohorts of patients with atrial fibrillation. Circulation. 2017;135(3):208–219.

20. Shah SJ, Eckman MH, Aspberg S, Go AS, Singer DE. Effect of variation in published stroke rates on the net clinical benefit of anticoagulation for atrial fibrillation. Ann Intern Med. 2018;169(8):517–527.

 

 

Copyright © 2019 by the American Academy of Family Physicians.
This content is owned by the AAFP. A person viewing it online may make one printout of the material and may use that printout only for his or her personal, non-commercial reference. This material may not otherwise be downloaded, copied, printed, stored, transmitted or reproduced in any medium, whether now known or later invented, except as authorized in writing by the AAFP. Contact afpserv@aafp.org for copyright questions and/or permission requests.

Want to use this article elsewhere? Get Permissions

CME Quiz

More in AFP


Editor's Collections


Related Content


More in Pubmed

MOST RECENT ISSUE


Apr 15, 2019

Access the latest issue of American Family Physician

Read the Issue


Email Alerts

Don't miss a single issue. Sign up for the free AFP email table of contents.

Sign Up Now

Navigate this Article