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Head-to-head comparison of two commonly used cardiac monitor patch devices suggested important differences, a real-world, simultaneous-wear study showed.

Bardy Diagnostics' Carnation long-term ECG device detected arrhythmia in twice as many patients as did Preventice Solutions' BodyGuardian mobile cardiac telemetry device during overlapping use (50% vs 24%, P=0.018).

The long-term ECG device also picked up substantially more events (61 vs 19, P<0.001), Mark E. Willcox, MD, of the Alaska Heart and Vascular Institute in Anchorage, reported at the hybrid Heart Rhythm Society (HRS) meeting, held online and in Boston.

The BodyGuardian mobile cardiac telemetry device picked up only one event that the other did not, a case of ventricular tachycardia, whereas the majority of events were picked up only by the Carnation ECG device.

"Not all monitors are created equal," Willcox concluded at an HRS press conference. "We all know from reading EKGs that computers aren't quite as good as human beings, yet we rely on them a lot in the outpatient world."

While there are a number of differences between the two that could account for the findings, a key feature is the way the data are read:

• The BodyGuardian device puts the data through algorithm-based detection with human interpretation for arrhythmias that are captured

• The Carnation device has humans read and interpret the strip initially, then supplemented by an algorithm

Willcox cautioned against overinterpreting or overgeneralizing the 46-patient study of just two devices: "We're not trying to say that one is clinically better than the other, because we are not comparing the clinical utility, just the diagnostic accuracy."

Even so, "this study does impact my decision-making as now we have to consider differences in arrhythmia detection and duration, whereas previously I assumed arrhythmia detection was similar," he said at an HRS press conference.

Session study discussant Roderick Tung, MD, of the University of Chicago, agreed: "In clinical decision making, how nervous does this make us when we are risk stratifying a patient for hypertrophic cardiomyopathy? They get a mobile, and then [if] there's no non-sustained VT [ventricular tachycardia], you don't take that as a risk factor. This is really enlightening and makes us realize everything we do has limitations."

He expressed amazement that such comparative studies haven't been done before now.

Wearables more generally are improving their sophistication and accuracy over time and are hugely popular, but such findings do raise questions of what role these devices should play in detection and management of arrhythmia, noted press conference moderator Andrew Krahn, MD, of the University of British Columbia in Vancouver, and president-elect of the HRS.

"It makes us really question when a manufacture says, 'I have a device for you to use, it's really good at detecting arrhythmias,'" Willcox said. "How do we know that is the truth?" There's no good gold standard against which to compare, as even implantable loop recorders may miss events, he said.

The two monitors selected for the study were what are clinically in use at his center and are among the most commonly used in the U.S., but there are a number of others on the market. "Manufacturers' processes can, and we hope will, change as algorithms improve," Willcox noted.

While the findings were somewhat surprising, the question of generalizability is unanswerable, said session study discussant Jeremy Ruskin, MD, of Massachusetts General Hospital in Boston.

The long-term ECG device appeared to distinguish itself on "outstanding P-wave discrimination," he noted.

The good news is that the long-term ECG device is actually cheaper, Willcox said. "This can be both cost effective and a little better perhaps."

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