The Ohio State University Wexner Medical Center employs eight nurses whose only job is to read the electronic transmissions flowing from thousands of implanted heart devices living in their patients' chests.
Like health-data workers across the U.S., the nurses at the Columbus, Ohio, medical center scan the transmissions every day for signs of problems like atrial fibrillation. Lately, though, the team was drowning in bad data thrown off by a popular implantable heart monitor, Medtronic's industry-leading Reveal Linq implantable loop recorder.
According to study results published online last month in the peer-reviewed Heart Rhythm journal, the team analyzed data on 559 consecutive Ohio State patients and found that between 46% and 86% of the health alerts sent by their implantable Medtronic heart monitors were false. "The average time to review one transmission and adjudication after consultation with electrophysiologist requires 30 to 45 minutes at our center," the study said. But Medtronic said it may only require one to two minutes to adjudicate a false positive.
Dr. Muhammad Afzal, corresponding author of the Heart Rhythm paper, said the number of false positives using devices with factory settings was "significant." Medtronic, which is run from offices in Fridley, stressed that the minimally invasive Linq device can be programmed by a doctor to tone down the detection of certain heart signals that may not be relevant to a particular patient, reducing time spent on false-positive transmissions.
Implantable heart monitors accounted for nearly $1 billion in sales worldwide last year and continue to grow, with Medtronic's Reveal Linq leading by a wide margin a market that includes monitors made by Abbott Laboratories and Biotronik, said Sean Messenger, a med-tech industry analyst with Decision Resources Group.
Smaller than a AAA battery, the Linq retails for slightly less than $5,000 to hospitals, analysts said, which can double that price or more in its bills to insurers.
The battery-powered devices can monitor for irregular heartbeats continuously for at least three years, making them more comprehensive than other forms of temporary heart monitors, like Holter monitors and temporary cardiac patches, which can read and record data for 24 hours to 14 days.
Medtronic said the Linq is effective at diagnosing problems that would have been undiagnosed otherwise. A 2017 report in JAMA Cardiology found that 40% of 385 patients who received the device at one of 57 different hospitals had episodes of atrial fibrillation detected after 30 months, with a median time-to-detection of 123 days.
Kentucky cardiologist Dr. John Mandrola, a frequent industry commentator who did not take part in the Ohio State study, said the false-positive rates reported in the recent Heart Rhythm article appeared to be "super high," especially for a device bearing a medical-grade price tag.
"False positives are a problem because not only do they give you a misdiagnosis, they can lead people to ... doing things they wouldn't otherwise do, like further testing and anti-coagulation," Mandrola said.
He will continue to use the Linq in his practice, with the settings customized to cut down on unneeded transmissions, but he said ultimately a study should look at the larger question of whether the devices are helping people avoid strokes and live longer.
Medtronic officials said it was "pure speculation" that patient risk has been created, and that the company never recommends treatment be given without having a medical expert adjudicate the device data.
Medtronic said Linq devices are intentionally shipped at high sensitivity because they are designed to look for evidence that has been missed by other diagnostic tools, like when someone has unexplained fainting spells known as "syncope" and doesn't know whether subtle heartbeat problems could be causing it.
Dr. Robert Kowal, chief medical officer for Medtronic's cardiac rhythm and heart failure division, said any diagnostic test must strike a balance between the sensitivity of the analysis and the amount of information produced.
"We are trying to err on [the side of] sensitivity, because of the severity of the patient illness," Kowal said. "With all these tests, you are trading sensitivity and specificity all the time. The good news with Linq is, we will continue to improve the algorithms, and also give the physician the ability to adjust those as it fits their patient needs."
For example, patients who get a Linq to look for the irregular heart rhythm called atrial fibrillation following a stroke of unknown origin, known as cryptogenic stroke (CS), can have alerts turned off for conditions like cardiac pause.
In the Ohio State study, 93% of the 46 reports of cardiac pause in patients with CS were found to be false positives.
Overall, 86% of all 78 transmissions in CS patients were found to be false positives, while 71% of the syncope patients' and 46% of the atrial fibrillation patients' were false positives.
Kowal pointed out that at least 15 people in the study were also correctly diagnosed with atrial fibrillation during the four-week study period.
Since the study was performed, Medtronic personnel have worked with the Ohio State clinicians on strategies to cut down the number of false positives and home in on alerts that are more meaningful, Afzal said.
"We started doing what we call custom programming. We implant the device and then whatever clinical information we are interested in, we program the device only for that. So all the information which we don't need, we turn off, or make the criteria very stringent, so that incidents of false positive go down," he said. Those efforts have led to what he called "good results," though he couldn't be specific since the results are not yet published.