A study published yesterday in the Journal of the American Medical Association (JAMA) raises important questions about the implications of widespread screening for atrial fibrillation — our most common abnormal heart rhythm (or, “arrhythmia”).
Atrial fibrillation (“AF” or “AFib” for short) is an irregular beating of the heart’s two upper chambers, and is considered a risk factor for stroke. The study looked at diagnosing AF — not by the traditional electrocardiogram (ECG) performed during an office visit — but by using a wearable, self-applied ECG patch; specifically, in people over age 55 at high risk for developing the arrhythmia.
The study found that at 4 months Afib was diagnosed in 53 out of 1,366 patients wearing the patch (3.9%) compared with 12 out of 1,293 patients (0.9%) in the control group; an absolute difference of 3%. After a full year the rate of AF diagnosis more than doubled in the monitored group (from 2.6 to 6.7 per 100 person-years).
The patch group also ended up with more treatment with anti-coagulants and heart rhythm drugs, as well as more utilization of healthcare resources (mainly cardiology consultations and pacemaker placements).
But it’s not these downstream consequences that get highlighted in news coverage. Take this story by HealthDay, which was picked up by WebMD, one of the most visited health websites in the world:
At two points it’s emphasized that “catching it early” (ie. before symptoms develop) “can lower the incidence of stroke.” That’s from a New York-based cardiologist, and it’s echoed by the lead author — Steven Steinhubl, MD, director of digital medicine at the Scripps Translational Science Institute, who’s quoted as saying:
“Timely diagnosis of afib more effectively can enable the initiation of effective therapies and help reduce strokes and death.”
That contradicts a statement he gave to the San Diego Union-Tribune:
“It remains to be seen if the higher diagnosis rate translates into better outcomes for patients.”
So which is it? Would patients benefit from treating the AFib picked up by this device? Or not?
“The fact that more intensive or prolonged monitoring would pick up more AFib is not surprising,” said Michael Joyner, MD, a researcher at the Mayo Clinic and frequent contributor to HealthNewsReview.org (including this article he wrote about what we do and don’t know about wearable monitors).
“But the study raises important questions about screening large populations: Who should get screened? What to do about the results? And, what’s the impact on outcomes like preventing stroke? Although this paper is really well done, and it sets the stage for more research about outcomes down the road, it doesn’t answer those questions.”
Do we know the answers to those questions? We don’t. Especially when it comes to what’s called “low burden” AF; that is, AFib that only lasts seconds or minutes (by contrast some AFib lasts days, weeks, or years and is considered more likely to lead to blood clots and possible stroke). Of note, most of the AF found in this study was low burden (ie. not persistent).
“The potential downside of this 24/7 wearable technology is that it will catch a lot of these brief, low burden episodes,” said cardiologist Chris Labos, MD.
“The worrisome trade-off becomes overdiagnosis and overtreatment because we have yet to figure out if we should be giving blood thinners (anticoagulants) to low burden AF patients, because there’s no proof such treatment will prevent strokes.”
Larry Husten is a journalist who’s made heart health his beat with his Cardiobrief blog. He was one of the first to write an analysis of yesterday’s JAMA article.
Husten raised some compelling points I didn’t see in any other news coverage:
“There’s a lot we don’t understand about Afib screening,” said John Mandrola MD, a Kentucky-based cardiologist who specializes in abnormal heart rhythms like AFib.
“We don’t have good outcome data. If you look at the number of people we need to screen, and the number of people we’d need to treat with anticoagulants, we’re unlikely to deliver substantial benefits. And it’s unlikely to be cost effective. Also, the typical AF screening test is just about 90% specific, so the false positive rate is 10%. That’s huge if the incidence of AFib is just 1-2% and you plan to screen millions of people.”
(Learn more about the problems with false-positive results from screening tests in our primer: “Understanding medical tests: sensitivity, specificity, and positive predictive value.”)
iRhythm Technologies — the California-based company that manufactures the “Zio Patch” used in this study — claims wearable technology is “redefining the way cardiac arrhythmias are clinically diagnosed.”
Although that may be true in one sense, it could also become a double-edged sword if it ends up redefining atrial fibrillation in such a broad way that overdiagnosis and overtreatment lead to remarkable profits for a few, at the expense of harms and unremarkable outcomes for the many.