Atrial fibrillation (or “afib”), the most common type of irregular heartbeat, is associated with an increased risk of stroke. For patients that seek medical care for afib symptoms, treatment with blood thinners has shown to help. So why not try catching afib early?
That’s the reasoning behind tracking heart rhythm with Apple Watches and other fitness monitor. However, a new review of the evidence from the US Preventive Services Task Force (USPSTF) finds that we still don’t have enough evidence to recommend screening asymptomatic low-risk people for afib.
In an related editorial in JAMA Internal Medicine, cardiologists John Mandrola and Andrew Foy break down the findings of two recent studies that looked at screening for asymptomatic afib. The STROKESTOP study invited 14,000 older adults to screen themselves twice a day with a handheld ECG monitor; 14,000 others were given standard care. After seven years, they found no significant difference in the rate of diagnosed afib or use of anticoagulants between the two groups. This suggests that “given time, standard care will discover most cases of afib,” the authors write.
The screened group had a 0.2% absolute difference in the primary outcome (a composite of various cardiac events), but given there was no difference in treatments, this might be due to chance. The authors note this small difference would not be significant if just one patient in the screened group had a different outcome.
“It is crucial that people understand the limits of early detection of surrogate markers of disease—because the digital revolution will only lead to more [of this].”
Dr. John Mandrola
In the LOOP study, about 6000 older adults were randomized to either have an implantable monitoring device or standard care. After about five years, they found that the screened group was 2.6 times as likely to have afib diagnosed and three times as likely to be put on anticoagulants. However, rates of stroke between the two groups were not significantly different. As Mandrola writes in a related blog post, “Implantable loop recorders are the best AF screening tool we have… if you can’t show a reduction in stroke with this device, less robust devices would be unlikely to work.”
Mandrola and Foy explain why finding more afib doesn’t necessarily translate to better outcomes. Afib is just one risk factor for stroke, so treating this condition does not necessarily reduce other potential risk factors. Also, we don’t know whether asymptomatic afib responds to anticoagulant treatment the way that symptomatic afib does.
In a way, the USPSTF is closing the barn door after the horse has already ran out. Whether screening for afib is effective or not, millions of people worldwide are already using an Apple Watch to track their heart rhythm. Mandrola and Foy outline some of their concerns with the increase in monitoring, such as anxiety, overtreatment, and waste. Doctors have reported already seeing some of the impacts of this monitoring, like overdiagnosis and care cascades.
However, the recommendation is still useful for patients and doctors as a caution that finding and treating an asymptomatic condition does not necessarily lead to better health. Mandrola writes, “It is crucial that people understand the limits of early detection of surrogate markers of disease—because the digital revolution will only lead to more [of this].”